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| author | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2015-08-05 17:04:01 -0300 |
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| committer | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2015-08-05 17:04:01 -0300 |
| commit | 57f0f512b273f60d52568b8c6b77e17f5636edc0 (patch) | |
| tree | 5e910f0e82173f4ef4f51111366a3f1299037a7b /Documentation/DocBook/media/v4l/pixfmt.xml | |
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diff --git a/Documentation/DocBook/media/v4l/pixfmt.xml b/Documentation/DocBook/media/v4l/pixfmt.xml new file mode 100644 index 000000000..fcde4e202 --- /dev/null +++ b/Documentation/DocBook/media/v4l/pixfmt.xml @@ -0,0 +1,1801 @@ + <title>Image Formats</title> + + <para>The V4L2 API was primarily designed for devices exchanging +image data with applications. The +<structname>v4l2_pix_format</structname> and <structname>v4l2_pix_format_mplane +</structname> structures define the format and layout of an image in memory. +The former is used with the single-planar API, while the latter is used with the +multi-planar version (see <xref linkend="planar-apis"/>). Image formats are +negotiated with the &VIDIOC-S-FMT; ioctl. (The explanations here focus on video +capturing and output, for overlay frame buffer formats see also +&VIDIOC-G-FBUF;.)</para> + +<section> + <title>Single-planar format structure</title> + <table pgwide="1" frame="none" id="v4l2-pix-format"> + <title>struct <structname>v4l2_pix_format</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>width</structfield></entry> + <entry>Image width in pixels.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>height</structfield></entry> + <entry>Image height in pixels. If <structfield>field</structfield> is + one of <constant>V4L2_FIELD_TOP</constant>, <constant>V4L2_FIELD_BOTTOM</constant> + or <constant>V4L2_FIELD_ALTERNATE</constant> then height refers to the + number of lines in the field, otherwise it refers to the number of + lines in the frame (which is twice the field height for interlaced + formats).</entry> + </row> + <row> + <entry spanname="hspan">Applications set these fields to +request an image size, drivers return the closest possible values. In +case of planar formats the <structfield>width</structfield> and +<structfield>height</structfield> applies to the largest plane. To +avoid ambiguities drivers must return values rounded up to a multiple +of the scale factor of any smaller planes. For example when the image +format is YUV 4:2:0, <structfield>width</structfield> and +<structfield>height</structfield> must be multiples of two.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>pixelformat</structfield></entry> + <entry>The pixel format or type of compression, set by the +application. This is a little endian <link +linkend="v4l2-fourcc">four character code</link>. V4L2 defines +standard RGB formats in <xref linkend="rgb-formats" />, YUV formats in <xref +linkend="yuv-formats" />, and reserved codes in <xref +linkend="reserved-formats" /></entry> + </row> + <row> + <entry>&v4l2-field;</entry> + <entry><structfield>field</structfield></entry> + <entry>Video images are typically interlaced. Applications +can request to capture or output only the top or bottom field, or both +fields interlaced or sequentially stored in one buffer or alternating +in separate buffers. Drivers return the actual field order selected. +For more details on fields see <xref linkend="field-order" />.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>bytesperline</structfield></entry> + <entry>Distance in bytes between the leftmost pixels in two +adjacent lines.</entry> + </row> + <row> + <entry spanname="hspan"><para>Both applications and drivers +can set this field to request padding bytes at the end of each line. +Drivers however may ignore the value requested by the application, +returning <structfield>width</structfield> times bytes per pixel or a +larger value required by the hardware. That implies applications can +just set this field to zero to get a reasonable +default.</para><para>Video hardware may access padding bytes, +therefore they must reside in accessible memory. Consider cases where +padding bytes after the last line of an image cross a system page +boundary. Input devices may write padding bytes, the value is +undefined. Output devices ignore the contents of padding +bytes.</para><para>When the image format is planar the +<structfield>bytesperline</structfield> value applies to the first +plane and is divided by the same factor as the +<structfield>width</structfield> field for the other planes. For +example the Cb and Cr planes of a YUV 4:2:0 image have half as many +padding bytes following each line as the Y plane. To avoid ambiguities +drivers must return a <structfield>bytesperline</structfield> value +rounded up to a multiple of the scale factor.</para> +<para>For compressed formats the <structfield>bytesperline</structfield> +value makes no sense. Applications and drivers must set this to 0 in +that case.</para></entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>sizeimage</structfield></entry> + <entry>Size in bytes of the buffer to hold a complete image, +set by the driver. Usually this is +<structfield>bytesperline</structfield> times +<structfield>height</structfield>. When the image consists of variable +length compressed data this is the maximum number of bytes required to +hold an image.</entry> + </row> + <row> + <entry>&v4l2-colorspace;</entry> + <entry><structfield>colorspace</structfield></entry> + <entry>This information supplements the +<structfield>pixelformat</structfield> and must be set by the driver for +capture streams and by the application for output streams, +see <xref linkend="colorspaces" />.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>priv</structfield></entry> + <entry><para>This field indicates whether the remaining fields of the +<structname>v4l2_pix_format</structname> structure, also called the extended +fields, are valid. When set to <constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, it +indicates that the extended fields have been correctly initialized. When set to +any other value it indicates that the extended fields contain undefined values. +</para> +<para>Applications that wish to use the pixel format extended fields must first +ensure that the feature is supported by querying the device for the +<link linkend="querycap"><constant>V4L2_CAP_EXT_PIX_FORMAT</constant></link> +capability. If the capability isn't set the pixel format extended fields are not +supported and using the extended fields will lead to undefined results.</para> +<para>To use the extended fields, applications must set the +<structfield>priv</structfield> field to +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, initialize all the extended fields +and zero the unused bytes of the <structname>v4l2_format</structname> +<structfield>raw_data</structfield> field.</para> +<para>When the <structfield>priv</structfield> field isn't set to +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> drivers must act as if all the +extended fields were set to zero. On return drivers must set the +<structfield>priv</structfield> field to +<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> and all the extended fields to +applicable values.</para></entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>flags</structfield></entry> + <entry>Flags set by the application or driver, see <xref +linkend="format-flags" />.</entry> + </row> + <row> + <entry>&v4l2-ycbcr-encoding;</entry> + <entry><structfield>ycbcr_enc</structfield></entry> + <entry>This information supplements the +<structfield>colorspace</structfield> and must be set by the driver for +capture streams and by the application for output streams, +see <xref linkend="colorspaces" />.</entry> + </row> + <row> + <entry>&v4l2-quantization;</entry> + <entry><structfield>quantization</structfield></entry> + <entry>This information supplements the +<structfield>colorspace</structfield> and must be set by the driver for +capture streams and by the application for output streams, +see <xref linkend="colorspaces" />.</entry> + </row> + </tbody> + </tgroup> + </table> +</section> + +<section> + <title>Multi-planar format structures</title> + <para>The <structname>v4l2_plane_pix_format</structname> structures define + size and layout for each of the planes in a multi-planar format. + The <structname>v4l2_pix_format_mplane</structname> structure contains + information common to all planes (such as image width and height) and + an array of <structname>v4l2_plane_pix_format</structname> structures, + describing all planes of that format.</para> + <table pgwide="1" frame="none" id="v4l2-plane-pix-format"> + <title>struct <structname>v4l2_plane_pix_format</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>sizeimage</structfield></entry> + <entry>Maximum size in bytes required for image data in this plane. + </entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>bytesperline</structfield></entry> + <entry>Distance in bytes between the leftmost pixels in two adjacent + lines. See &v4l2-pix-format;.</entry> + </row> + <row> + <entry>__u16</entry> + <entry><structfield>reserved[6]</structfield></entry> + <entry>Reserved for future extensions. Should be zeroed by the + application.</entry> + </row> + </tbody> + </tgroup> + </table> + <table pgwide="1" frame="none" id="v4l2-pix-format-mplane"> + <title>struct <structname>v4l2_pix_format_mplane</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>width</structfield></entry> + <entry>Image width in pixels. See &v4l2-pix-format;.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>height</structfield></entry> + <entry>Image height in pixels. See &v4l2-pix-format;.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>pixelformat</structfield></entry> + <entry>The pixel format. Both single- and multi-planar four character +codes can be used.</entry> + </row> + <row> + <entry>&v4l2-field;</entry> + <entry><structfield>field</structfield></entry> + <entry>See &v4l2-pix-format;.</entry> + </row> + <row> + <entry>&v4l2-colorspace;</entry> + <entry><structfield>colorspace</structfield></entry> + <entry>See &v4l2-pix-format;.</entry> + </row> + <row> + <entry>&v4l2-plane-pix-format;</entry> + <entry><structfield>plane_fmt[VIDEO_MAX_PLANES]</structfield></entry> + <entry>An array of structures describing format of each plane this + pixel format consists of. The number of valid entries in this array + has to be put in the <structfield>num_planes</structfield> + field.</entry> + </row> + <row> + <entry>__u8</entry> + <entry><structfield>num_planes</structfield></entry> + <entry>Number of planes (i.e. separate memory buffers) for this format + and the number of valid entries in the + <structfield>plane_fmt</structfield> array.</entry> + </row> + <row> + <entry>__u8</entry> + <entry><structfield>flags</structfield></entry> + <entry>Flags set by the application or driver, see <xref +linkend="format-flags" />.</entry> + </row> + <row> + <entry>&v4l2-ycbcr-encoding;</entry> + <entry><structfield>ycbcr_enc</structfield></entry> + <entry>This information supplements the +<structfield>colorspace</structfield> and must be set by the driver for +capture streams and by the application for output streams, +see <xref linkend="colorspaces" />.</entry> + </row> + <row> + <entry>&v4l2-quantization;</entry> + <entry><structfield>quantization</structfield></entry> + <entry>This information supplements the +<structfield>colorspace</structfield> and must be set by the driver for +capture streams and by the application for output streams, +see <xref linkend="colorspaces" />.</entry> + </row> + <row> + <entry>__u8</entry> + <entry><structfield>reserved[8]</structfield></entry> + <entry>Reserved for future extensions. Should be zeroed by the + application.</entry> + </row> + </tbody> + </tgroup> + </table> +</section> + + <section> + <title>Standard Image Formats</title> + + <para>In order to exchange images between drivers and +applications, it is necessary to have standard image data formats +which both sides will interpret the same way. V4L2 includes several +such formats, and this section is intended to be an unambiguous +specification of the standard image data formats in V4L2.</para> + + <para>V4L2 drivers are not limited to these formats, however. +Driver-specific formats are possible. In that case the application may +depend on a codec to convert images to one of the standard formats +when needed. But the data can still be stored and retrieved in the +proprietary format. For example, a device may support a proprietary +compressed format. Applications can still capture and save the data in +the compressed format, saving much disk space, and later use a codec +to convert the images to the X Windows screen format when the video is +to be displayed.</para> + + <para>Even so, ultimately, some standard formats are needed, so +the V4L2 specification would not be complete without well-defined +standard formats.</para> + + <para>The V4L2 standard formats are mainly uncompressed formats. The +pixels are always arranged in memory from left to right, and from top +to bottom. The first byte of data in the image buffer is always for +the leftmost pixel of the topmost row. Following that is the pixel +immediately to its right, and so on until the end of the top row of +pixels. Following the rightmost pixel of the row there may be zero or +more bytes of padding to guarantee that each row of pixel data has a +certain alignment. Following the pad bytes, if any, is data for the +leftmost pixel of the second row from the top, and so on. The last row +has just as many pad bytes after it as the other rows.</para> + + <para>In V4L2 each format has an identifier which looks like +<constant>PIX_FMT_XXX</constant>, defined in the <link +linkend="videodev">videodev2.h</link> header file. These identifiers +represent <link linkend="v4l2-fourcc">four character (FourCC) codes</link> +which are also listed below, however they are not the same as those +used in the Windows world.</para> + + <para>For some formats, data is stored in separate, discontiguous +memory buffers. Those formats are identified by a separate set of FourCC codes +and are referred to as "multi-planar formats". For example, a YUV422 frame is +normally stored in one memory buffer, but it can also be placed in two or three +separate buffers, with Y component in one buffer and CbCr components in another +in the 2-planar version or with each component in its own buffer in the +3-planar case. Those sub-buffers are referred to as "planes".</para> + </section> + + <section id="colorspaces"> + <title>Colorspaces</title> + + <para>'Color' is a very complex concept and depends on physics, chemistry and +biology. Just because you have three numbers that describe the 'red', 'green' +and 'blue' components of the color of a pixel does not mean that you can accurately +display that color. A colorspace defines what it actually <emphasis>means</emphasis> +to have an RGB value of e.g. (255, 0, 0). That is, which color should be +reproduced on the screen in a perfectly calibrated environment.</para> + + <para>In order to do that we first need to have a good definition of +color, i.e. some way to uniquely and unambiguously define a color so that someone +else can reproduce it. Human color vision is trichromatic since the human eye has +color receptors that are sensitive to three different wavelengths of light. Hence +the need to use three numbers to describe color. Be glad you are not a mantis shrimp +as those are sensitive to 12 different wavelengths, so instead of RGB we would be +using the ABCDEFGHIJKL colorspace...</para> + + <para>Color exists only in the eye and brain and is the result of how strongly +color receptors are stimulated. This is based on the Spectral +Power Distribution (SPD) which is a graph showing the intensity (radiant power) +of the light at wavelengths covering the visible spectrum as it enters the eye. +The science of colorimetry is about the relationship between the SPD and color as +perceived by the human brain.</para> + + <para>Since the human eye has only three color receptors it is perfectly +possible that different SPDs will result in the same stimulation of those receptors +and are perceived as the same color, even though the SPD of the light is +different.</para> + + <para>In the 1920s experiments were devised to determine the relationship +between SPDs and the perceived color and that resulted in the CIE 1931 standard +that defines spectral weighting functions that model the perception of color. +Specifically that standard defines functions that can take an SPD and calculate +the stimulus for each color receptor. After some further mathematical transforms +these stimuli are known as the <emphasis>CIE XYZ tristimulus</emphasis> values +and these X, Y and Z values describe a color as perceived by a human unambiguously. +These X, Y and Z values are all in the range [0…1].</para> + + <para>The Y value in the CIE XYZ colorspace corresponds to luminance. Often +the CIE XYZ colorspace is transformed to the normalized CIE xyY colorspace:</para> + + <para>x = X / (X + Y + Z)</para> + <para>y = Y / (X + Y + Z)</para> + + <para>The x and y values are the chromaticity coordinates and can be used to +define a color without the luminance component Y. It is very confusing to +have such similar names for these colorspaces. Just be aware that if colors +are specified with lower case 'x' and 'y', then the CIE xyY colorspace is +used. Upper case 'X' and 'Y' refer to the CIE XYZ colorspace. Also, y has nothing +to do with luminance. Together x and y specify a color, and Y the luminance. +That is really all you need to remember from a practical point of view. At +the end of this section you will find reading resources that go into much more +detail if you are interested. +</para> + + <para>A monitor or TV will reproduce colors by emitting light at three +different wavelengths, the combination of which will stimulate the color receptors +in the eye and thus cause the perception of color. Historically these wavelengths +were defined by the red, green and blue phosphors used in the displays. These +<emphasis>color primaries</emphasis> are part of what defines a colorspace.</para> + + <para>Different display devices will have different primaries and some +primaries are more suitable for some display technologies than others. This has +resulted in a variety of colorspaces that are used for different display +technologies or uses. To define a colorspace you need to define the three +color primaries (these are typically defined as x, y chromaticity coordinates +from the CIE xyY colorspace) but also the white reference: that is the color obtained +when all three primaries are at maximum power. This determines the relative power +or energy of the primaries. This is usually chosen to be close to daylight which has +been defined as the CIE D65 Illuminant.</para> + + <para>To recapitulate: the CIE XYZ colorspace uniquely identifies colors. +Other colorspaces are defined by three chromaticity coordinates defined in the +CIE xyY colorspace. Based on those a 3x3 matrix can be constructed that +transforms CIE XYZ colors to colors in the new colorspace. +</para> + + <para>Both the CIE XYZ and the RGB colorspace that are derived from the +specific chromaticity primaries are linear colorspaces. But neither the eye, +nor display technology is linear. Doubling the values of all components in +the linear colorspace will not be perceived as twice the intensity of the color. +So each colorspace also defines a transfer function that takes a linear color +component value and transforms it to the non-linear component value, which is a +closer match to the non-linear performance of both the eye and displays. Linear +component values are denoted RGB, non-linear are denoted as R'G'B'. In general +colors used in graphics are all R'G'B', except in openGL which uses linear RGB. +Special care should be taken when dealing with openGL to provide linear RGB colors +or to use the built-in openGL support to apply the inverse transfer function.</para> + + <para>The final piece that defines a colorspace is a function that +transforms non-linear R'G'B' to non-linear Y'CbCr. This function is determined +by the so-called luma coefficients. There may be multiple possible Y'CbCr +encodings allowed for the same colorspace. Many encodings of color +prefer to use luma (Y') and chroma (CbCr) instead of R'G'B'. Since the human +eye is more sensitive to differences in luminance than in color this encoding +allows one to reduce the amount of color information compared to the luma +data. Note that the luma (Y') is unrelated to the Y in the CIE XYZ colorspace. +Also note that Y'CbCr is often called YCbCr or YUV even though these are +strictly speaking wrong.</para> + + <para>Sometimes people confuse Y'CbCr as being a colorspace. This is not +correct, it is just an encoding of an R'G'B' color into luma and chroma +values. The underlying colorspace that is associated with the R'G'B' color +is also associated with the Y'CbCr color.</para> + + <para>The final step is how the RGB, R'G'B' or Y'CbCr values are +quantized. The CIE XYZ colorspace where X, Y and Z are in the range +[0…1] describes all colors that humans can perceive, but the transform to +another colorspace will produce colors that are outside the [0…1] range. +Once clamped to the [0…1] range those colors can no longer be reproduced +in that colorspace. This clamping is what reduces the extent or gamut of the +colorspace. How the range of [0…1] is translated to integer values in the +range of [0…255] (or higher, depending on the color depth) is called the +quantization. This is <emphasis>not</emphasis> part of the colorspace +definition. In practice RGB or R'G'B' values are full range, i.e. they +use the full [0…255] range. Y'CbCr values on the other hand are limited +range with Y' using [16…235] and Cb and Cr using [16…240].</para> + + <para>Unfortunately, in some cases limited range RGB is also used +where the components use the range [16…235]. And full range Y'CbCr also exists +using the [0…255] range.</para> + + <para>In order to correctly interpret a color you need to know the +quantization range, whether it is R'G'B' or Y'CbCr, the used Y'CbCr encoding +and the colorspace. +From that information you can calculate the corresponding CIE XYZ color +and map that again to whatever colorspace your display device uses.</para> + + <para>The colorspace definition itself consists of the three +chromaticity primaries, the white reference chromaticity, a transfer +function and the luma coefficients needed to transform R'G'B' to Y'CbCr. While +some colorspace standards correctly define all four, quite often the colorspace +standard only defines some, and you have to rely on other standards for +the missing pieces. The fact that colorspaces are often a mix of different +standards also led to very confusing naming conventions where the name of +a standard was used to name a colorspace when in fact that standard was +part of various other colorspaces as well.</para> + + <para>If you want to read more about colors and colorspaces, then the +following resources are useful: <xref linkend="poynton" /> is a good practical +book for video engineers, <xref linkend="colimg" /> has a much broader scope and +describes many more aspects of color (physics, chemistry, biology, etc.). +The <ulink url="http://www.brucelindbloom.com">http://www.brucelindbloom.com</ulink> +website is an excellent resource, especially with respect to the mathematics behind +colorspace conversions. The wikipedia <ulink url="http://en.wikipedia.org/wiki/CIE_1931_color_space#CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space">CIE 1931 colorspace</ulink> article +is also very useful.</para> + </section> + + <section> + <title>Defining Colorspaces in V4L2</title> + <para>In V4L2 colorspaces are defined by three values. The first is the colorspace +identifier (&v4l2-colorspace;) which defines the chromaticities, the transfer +function, the default Y'CbCr encoding and the default quantization method. The second +is the Y'CbCr encoding identifier (&v4l2-ycbcr-encoding;) to specify non-standard +Y'CbCr encodings and the third is the quantization identifier (&v4l2-quantization;) +to specify non-standard quantization methods. Most of the time only the colorspace +field of &v4l2-pix-format; or &v4l2-pix-format-mplane; needs to be filled in. Note +that the default R'G'B' quantization is full range for all colorspaces except for +BT.2020 which uses limited range R'G'B' quantization.</para> + + <table pgwide="1" frame="none" id="v4l2-colorspace"> + <title>V4L2 Colorspaces</title> + <tgroup cols="2" align="left"> + &cs-def; + <thead> + <row> + <entry>Identifier</entry> + <entry>Details</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry><constant>V4L2_COLORSPACE_SMPTE170M</constant></entry> + <entry>See <xref linkend="col-smpte-170m" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_REC709</constant></entry> + <entry>See <xref linkend="col-rec709" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_SRGB</constant></entry> + <entry>See <xref linkend="col-srgb" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_ADOBERGB</constant></entry> + <entry>See <xref linkend="col-adobergb" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_BT2020</constant></entry> + <entry>See <xref linkend="col-bt2020" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_SMPTE240M</constant></entry> + <entry>See <xref linkend="col-smpte-240m" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_470_SYSTEM_M</constant></entry> + <entry>See <xref linkend="col-sysm" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_470_SYSTEM_BG</constant></entry> + <entry>See <xref linkend="col-sysbg" />.</entry> + </row> + <row> + <entry><constant>V4L2_COLORSPACE_JPEG</constant></entry> + <entry>See <xref linkend="col-jpeg" />.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-ycbcr-encoding"> + <title>V4L2 Y'CbCr Encodings</title> + <tgroup cols="2" align="left"> + &cs-def; + <thead> + <row> + <entry>Identifier</entry> + <entry>Details</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry><constant>V4L2_YCBCR_ENC_DEFAULT</constant></entry> + <entry>Use the default Y'CbCr encoding as defined by the colorspace.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_601</constant></entry> + <entry>Use the BT.601 Y'CbCr encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_709</constant></entry> + <entry>Use the Rec. 709 Y'CbCr encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_XV601</constant></entry> + <entry>Use the extended gamut xvYCC BT.601 encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_XV709</constant></entry> + <entry>Use the extended gamut xvYCC Rec. 709 encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_SYCC</constant></entry> + <entry>Use the extended gamut sYCC encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_BT2020</constant></entry> + <entry>Use the default non-constant luminance BT.2020 Y'CbCr encoding.</entry> + </row> + <row> + <entry><constant>V4L2_YCBCR_ENC_BT2020_CONST_LUM</constant></entry> + <entry>Use the constant luminance BT.2020 Yc'CbcCrc encoding.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-quantization"> + <title>V4L2 Quantization Methods</title> + <tgroup cols="2" align="left"> + &cs-def; + <thead> + <row> + <entry>Identifier</entry> + <entry>Details</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry><constant>V4L2_QUANTIZATION_DEFAULT</constant></entry> + <entry>Use the default quantization encoding as defined by the colorspace. +This is always full range for R'G'B' (except for the BT.2020 colorspace) and usually +limited range for Y'CbCr.</entry> + </row> + <row> + <entry><constant>V4L2_QUANTIZATION_FULL_RANGE</constant></entry> + <entry>Use the full range quantization encoding. I.e. the range [0…1] +is mapped to [0…255] (with possible clipping to [1…254] to avoid the +0x00 and 0xff values). Cb and Cr are mapped from [-0.5…0.5] to [0…255] +(with possible clipping to [1…254] to avoid the 0x00 and 0xff values).</entry> + </row> + <row> + <entry><constant>V4L2_QUANTIZATION_LIM_RANGE</constant></entry> + <entry>Use the limited range quantization encoding. I.e. the range [0…1] +is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to [16…240]. +</entry> + </row> + </tbody> + </tgroup> + </table> + </section> + + <section> + <title>Detailed Colorspace Descriptions</title> + <section id="col-smpte-170m"> + <title>Colorspace SMPTE 170M (<constant>V4L2_COLORSPACE_SMPTE170M</constant>)</title> + <para>The <xref linkend="smpte170m" /> standard defines the colorspace used by NTSC and PAL and by SDTV +in general. The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>. +The default Y'CbCr quantization is limited range. The chromaticities of the primary colors and +the white reference are:</para> + <table frame="none"> + <title>SMPTE 170M Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.630</entry> + <entry>0.340</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.310</entry> + <entry>0.595</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.155</entry> + <entry>0.070</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <para>The red, green and blue chromaticities are also often referred to +as the SMPTE C set, so this colorspace is sometimes called SMPTE C as well.</para> + <variablelist> + <varlistentry> + <term>The transfer function defined for SMPTE 170M is the same as the +one defined in Rec. 709.</term> + <listitem> + <para>L' = -1.099(-L)<superscript>0.45</superscript> + 0.099 for L ≤ -0.018</para> + <para>L' = 4.5L for -0.018 < L < 0.018</para> + <para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for L ≥ 0.018</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = -((L' - 0.099) / -1.099)<superscript>1/0.45</superscript> for L' ≤ -0.081</para> + <para>L = L' / 4.5 for -0.081 < L' < 0.081</para> + <para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with +the following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term> + <listitem> + <para>Y' = 0.299R' + 0.587G' + 0.114B'</para> + <para>Cb = -0.169R' - 0.331G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.419G' - 0.081B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5]. This conversion to Y'CbCr is identical to the one +defined in the <xref linkend="itu601" /> standard and this colorspace is sometimes called BT.601 as well, even +though BT.601 does not mention any color primaries.</para> + <para>The default quantization is limited range, but full range is possible although +rarely seen.</para> + </section> + + <section id="col-rec709"> + <title>Colorspace Rec. 709 (<constant>V4L2_COLORSPACE_REC709</constant>)</title> + <para>The <xref linkend="itu709" /> standard defines the colorspace used by HDTV in general. The default +Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_709</constant>. The default Y'CbCr quantization is +limited range. The chromaticities of the primary colors and the white reference are:</para> + <table frame="none"> + <title>Rec. 709 Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.640</entry> + <entry>0.330</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.300</entry> + <entry>0.600</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.150</entry> + <entry>0.060</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <para>The full name of this standard is Rec. ITU-R BT.709-5.</para> + <variablelist> + <varlistentry> + <term>Transfer function. Normally L is in the range [0…1], but for the extended +gamut xvYCC encoding values outside that range are allowed.</term> + <listitem> + <para>L' = -1.099(-L)<superscript>0.45</superscript> + 0.099 for L ≤ -0.018</para> + <para>L' = 4.5L for -0.018 < L < 0.018</para> + <para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for L ≥ 0.018</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = -((L' - 0.099) / -1.099)<superscript>1/0.45</superscript> for L' ≤ -0.081</para> + <para>L = L' / 4.5 for -0.081 < L' < 0.081</para> + <para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the following +<constant>V4L2_YCBCR_ENC_709</constant> encoding:</term> + <listitem> + <para>Y' = 0.2126R' + 0.7152G' + 0.0722B'</para> + <para>Cb = -0.1146R' - 0.3854G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.4542G' - 0.0458B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5].</para> + <para>The default quantization is limited range, but full range is possible although +rarely seen.</para> + <para>The <constant>V4L2_YCBCR_ENC_709</constant> encoding described above is the default +for this colorspace, but it can be overridden with <constant>V4L2_YCBCR_ENC_601</constant>, in which +case the BT.601 Y'CbCr encoding is used.</para> + <para>Two additional extended gamut Y'CbCr encodings are also possible with this colorspace:</para> + <variablelist> + <varlistentry> + <term>The xvYCC 709 encoding (<constant>V4L2_YCBCR_ENC_XV709</constant>, <xref linkend="xvycc" />) +is similar to the Rec. 709 encoding, but it allows for R', G' and B' values that are outside the range +[0…1]. The resulting Y', Cb and Cr values are scaled and offset:</term> + <listitem> + <para>Y' = (219 / 256) * (0.2126R' + 0.7152G' + 0.0722B') + (16 / 256)</para> + <para>Cb = (224 / 256) * (-0.1146R' - 0.3854G' + 0.5B')</para> + <para>Cr = (224 / 256) * (0.5R' - 0.4542G' - 0.0458B')</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The xvYCC 601 encoding (<constant>V4L2_YCBCR_ENC_XV601</constant>, <xref linkend="xvycc" />) is similar +to the BT.601 encoding, but it allows for R', G' and B' values that are outside the range +[0…1]. The resulting Y', Cb and Cr values are scaled and offset:</term> + <listitem> + <para>Y' = (219 / 256) * (0.299R' + 0.587G' + 0.114B') + (16 / 256)</para> + <para>Cb = (224 / 256) * (-0.169R' - 0.331G' + 0.5B')</para> + <para>Cr = (224 / 256) * (0.5R' - 0.419G' - 0.081B')</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are clamped +to the range [-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be used by +selecting <constant>V4L2_YCBCR_ENC_XV709</constant> or <constant>V4L2_YCBCR_ENC_XV601</constant>. +The xvYCC encodings always use full range quantization.</para> + </section> + + <section id="col-srgb"> + <title>Colorspace sRGB (<constant>V4L2_COLORSPACE_SRGB</constant>)</title> + <para>The <xref linkend="srgb" /> standard defines the colorspace used by most webcams and computer graphics. The +default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_SYCC</constant>. The default Y'CbCr quantization +is full range. The chromaticities of the primary colors and the white reference are:</para> + <table frame="none"> + <title>sRGB Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.640</entry> + <entry>0.330</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.300</entry> + <entry>0.600</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.150</entry> + <entry>0.060</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <para>These chromaticities are identical to the Rec. 709 colorspace.</para> + <variablelist> + <varlistentry> + <term>Transfer function. Note that negative values for L are only used by the Y'CbCr conversion.</term> + <listitem> + <para>L' = -1.055(-L)<superscript>1/2.4</superscript> + 0.055 for L < -0.0031308</para> + <para>L' = 12.92L for -0.0031308 ≤ L ≤ 0.0031308</para> + <para>L' = 1.055L<superscript>1/2.4</superscript> - 0.055 for 0.0031308 < L ≤ 1</para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = -((-L' + 0.055) / 1.055)<superscript>2.4</superscript> for L' < -0.04045</para> + <para>L = L' / 12.92 for -0.04045 ≤ L' ≤ 0.04045</para> + <para>L = ((L' + 0.055) / 1.055)<superscript>2.4</superscript> for L' > 0.04045</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the following +<constant>V4L2_YCBCR_ENC_SYCC</constant> encoding as defined by <xref linkend="sycc" />:</term> + <listitem> + <para>Y' = 0.2990R' + 0.5870G' + 0.1140B'</para> + <para>Cb = -0.1687R' - 0.3313G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.4187G' - 0.0813B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are clamped +to the range [-0.5…0.5]. The <constant>V4L2_YCBCR_ENC_SYCC</constant> quantization is always +full range. Although this Y'CbCr encoding looks very similar to the <constant>V4L2_YCBCR_ENC_XV601</constant> +encoding, it is not. The <constant>V4L2_YCBCR_ENC_XV601</constant> scales and offsets the Y'CbCr +values before quantization, but this encoding does not do that.</para> + </section> + + <section id="col-adobergb"> + <title>Colorspace Adobe RGB (<constant>V4L2_COLORSPACE_ADOBERGB</constant>)</title> + <para>The <xref linkend="adobergb" /> standard defines the colorspace used by computer graphics +that use the AdobeRGB colorspace. This is also known as the <xref linkend="oprgb" /> standard. +The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>. The default Y'CbCr +quantization is limited range. The chromaticities of the primary colors and the white reference +are:</para> + <table frame="none"> + <title>Adobe RGB Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.6400</entry> + <entry>0.3300</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.2100</entry> + <entry>0.7100</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.1500</entry> + <entry>0.0600</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <variablelist> + <varlistentry> + <term>Transfer function:</term> + <listitem> + <para>L' = L<superscript>1/2.19921875</superscript></para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = L'<superscript>2.19921875</superscript></para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the +following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term> + <listitem> + <para>Y' = 0.299R' + 0.587G' + 0.114B'</para> + <para>Cb = -0.169R' - 0.331G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.419G' - 0.081B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5]. This transform is identical to one defined in +SMPTE 170M/BT.601. The Y'CbCr quantization is limited range.</para> + </section> + + <section id="col-bt2020"> + <title>Colorspace BT.2020 (<constant>V4L2_COLORSPACE_BT2020</constant>)</title> + <para>The <xref linkend="itu2020" /> standard defines the colorspace used by Ultra-high definition +television (UHDTV). The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_BT2020</constant>. +The default R'G'B' quantization is limited range (!), and so is the default Y'CbCr quantization. +The chromaticities of the primary colors and the white reference are:</para> + <table frame="none"> + <title>BT.2020 Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.708</entry> + <entry>0.292</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.170</entry> + <entry>0.797</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.131</entry> + <entry>0.046</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <variablelist> + <varlistentry> + <term>Transfer function (same as Rec. 709):</term> + <listitem> + <para>L' = 4.5L for 0 ≤ L < 0.018</para> + <para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = L' / 4.5 for L' < 0.081</para> + <para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the +following <constant>V4L2_YCBCR_ENC_BT2020</constant> encoding:</term> + <listitem> + <para>Y' = 0.2627R' + 0.6780G' + 0.0593B'</para> + <para>Cb = -0.1396R' - 0.3604G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.4598G' - 0.0402B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.</para> + <para>There is also an alternate constant luminance R'G'B' to Yc'CbcCrc +(<constant>V4L2_YCBCR_ENC_BT2020_CONST_LUM</constant>) encoding:</para> + <variablelist> + <varlistentry> + <term>Luma:</term> + <listitem> + <para>Yc' = (0.2627R + 0.6780G + 0.0593B)'</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>B' - Yc' ≤ 0:</term> + <listitem> + <para>Cbc = (B' - Yc') / 1.9404</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>B' - Yc' > 0:</term> + <listitem> + <para>Cbc = (B' - Yc') / 1.5816</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>R' - Yc' ≤ 0:</term> + <listitem> + <para>Crc = (R' - Y') / 1.7184</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>R' - Yc' > 0:</term> + <listitem> + <para>Crc = (R' - Y') / 0.9936</para> + </listitem> + </varlistentry> + </variablelist> + <para>Yc' is clamped to the range [0…1] and Cbc and Crc are +clamped to the range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.</para> + </section> + + <section id="col-smpte-240m"> + <title>Colorspace SMPTE 240M (<constant>V4L2_COLORSPACE_SMPTE240M</constant>)</title> + <para>The <xref linkend="smpte240m" /> standard was an interim standard used during the early days of HDTV (1988-1998). +It has been superseded by Rec. 709. The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_SMPTE240M</constant>. +The default Y'CbCr quantization is limited range. The chromaticities of the primary colors and the +white reference are:</para> + <table frame="none"> + <title>SMPTE 240M Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.630</entry> + <entry>0.340</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.310</entry> + <entry>0.595</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.155</entry> + <entry>0.070</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <para>These chromaticities are identical to the SMPTE 170M colorspace.</para> + <variablelist> + <varlistentry> + <term>Transfer function:</term> + <listitem> + <para>L' = 4L for 0 ≤ L < 0.0228</para> + <para>L' = 1.1115L<superscript>0.45</superscript> - 0.1115 for 0.0228 ≤ L ≤ 1</para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = L' / 4 for 0 ≤ L' < 0.0913</para> + <para>L = ((L' + 0.1115) / 1.1115)<superscript>1/0.45</superscript> for L' ≥ 0.0913</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the +following <constant>V4L2_YCBCR_ENC_SMPTE240M</constant> encoding:</term> + <listitem> + <para>Y' = 0.2122R' + 0.7013G' + 0.0865B'</para> + <para>Cb = -0.1161R' - 0.3839G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.4451G' - 0.0549B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Yc' is clamped to the range [0…1] and Cbc and Crc are +clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.</para> + </section> + + <section id="col-sysm"> + <title>Colorspace NTSC 1953 (<constant>V4L2_COLORSPACE_470_SYSTEM_M</constant>)</title> + <para>This standard defines the colorspace used by NTSC in 1953. In practice this +colorspace is obsolete and SMPTE 170M should be used instead. The default Y'CbCr encoding +is <constant>V4L2_YCBCR_ENC_601</constant>. The default Y'CbCr quantization is limited range. +The chromaticities of the primary colors and the white reference are:</para> + <table frame="none"> + <title>NTSC 1953 Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.67</entry> + <entry>0.33</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.21</entry> + <entry>0.71</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.14</entry> + <entry>0.08</entry> + </row> + <row> + <entry>White Reference (C)</entry> + <entry>0.310</entry> + <entry>0.316</entry> + </row> + </tbody> + </tgroup> + </table> + <para>Note that this colorspace uses Illuminant C instead of D65 as the +white reference. To correctly convert an image in this colorspace to another +that uses D65 you need to apply a chromatic adaptation algorithm such as the +Bradford method.</para> + <variablelist> + <varlistentry> + <term>The transfer function was never properly defined for NTSC 1953. The +Rec. 709 transfer function is recommended in the literature:</term> + <listitem> + <para>L' = 4.5L for 0 ≤ L < 0.018</para> + <para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = L' / 4.5 for L' < 0.081</para> + <para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the +following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term> + <listitem> + <para>Y' = 0.299R' + 0.587G' + 0.114B'</para> + <para>Cb = -0.169R' - 0.331G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.419G' - 0.081B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range. +This transform is identical to one defined in SMPTE 170M/BT.601.</para> + </section> + + <section id="col-sysbg"> + <title>Colorspace EBU Tech. 3213 (<constant>V4L2_COLORSPACE_470_SYSTEM_BG</constant>)</title> + <para>The <xref linkend="tech3213" /> standard defines the colorspace used by PAL/SECAM in 1975. In practice this +colorspace is obsolete and SMPTE 170M should be used instead. The default Y'CbCr encoding +is <constant>V4L2_YCBCR_ENC_601</constant>. The default Y'CbCr quantization is limited range. +The chromaticities of the primary colors and the white reference are:</para> + <table frame="none"> + <title>EBU Tech. 3213 Chromaticities</title> + <tgroup cols="3" align="left"> + &cs-str; + <thead> + <row> + <entry>Color</entry> + <entry>x</entry> + <entry>y</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry>Red</entry> + <entry>0.64</entry> + <entry>0.33</entry> + </row> + <row> + <entry>Green</entry> + <entry>0.29</entry> + <entry>0.60</entry> + </row> + <row> + <entry>Blue</entry> + <entry>0.15</entry> + <entry>0.06</entry> + </row> + <row> + <entry>White Reference (D65)</entry> + <entry>0.3127</entry> + <entry>0.3290</entry> + </row> + </tbody> + </tgroup> + </table> + <variablelist> + <varlistentry> + <term>The transfer function was never properly defined for this colorspace. +The Rec. 709 transfer function is recommended in the literature:</term> + <listitem> + <para>L' = 4.5L for 0 ≤ L < 0.018</para> + <para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para> + </listitem> + </varlistentry> + <varlistentry> + <term>Inverse Transfer function:</term> + <listitem> + <para>L = L' / 4.5 for L' < 0.081</para> + <para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para> + </listitem> + </varlistentry> + </variablelist> + <variablelist> + <varlistentry> + <term>The luminance (Y') and color difference (Cb and Cr) are obtained with the +following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term> + <listitem> + <para>Y' = 0.299R' + 0.587G' + 0.114B'</para> + <para>Cb = -0.169R' - 0.331G' + 0.5B'</para> + <para>Cr = 0.5R' - 0.419G' - 0.081B'</para> + </listitem> + </varlistentry> + </variablelist> + <para>Y' is clamped to the range [0…1] and Cb and Cr are +clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range. +This transform is identical to one defined in SMPTE 170M/BT.601.</para> + </section> + + <section id="col-jpeg"> + <title>Colorspace JPEG (<constant>V4L2_COLORSPACE_JPEG</constant>)</title> + <para>This colorspace defines the colorspace used by most (Motion-)JPEG formats. The chromaticities +of the primary colors and the white reference are identical to sRGB. The Y'CbCr encoding is +<constant>V4L2_YCBCR_ENC_601</constant> with full range quantization where +Y' is scaled to [0…255] and Cb/Cr are scaled to [-128…128] and +then clipped to [-128…127].</para> + <para>Note that the JPEG standard does not actually store colorspace information. +So if something other than sRGB is used, then the driver will have to set that information +explicitly. Effectively <constant>V4L2_COLORSPACE_JPEG</constant> can be considered to be +an abbreviation for <constant>V4L2_COLORSPACE_SRGB</constant>, <constant>V4L2_YCBCR_ENC_601</constant> +and <constant>V4L2_QUANTIZATION_FULL_RANGE</constant>.</para> + </section> + + </section> + + <section id="pixfmt-indexed"> + <title>Indexed Format</title> + + <para>In this format each pixel is represented by an 8 bit index +into a 256 entry ARGB palette. It is intended for <link +linkend="osd">Video Output Overlays</link> only. There are no ioctls to +access the palette, this must be done with ioctls of the Linux framebuffer API.</para> + + <table pgwide="0" frame="none"> + <title>Indexed Image Format</title> + <tgroup cols="37" align="center"> + <colspec colname="id" align="left" /> + <colspec colname="fourcc" /> + <colspec colname="bit" /> + + <colspec colnum="4" colname="b07" align="center" /> + <colspec colnum="5" colname="b06" align="center" /> + <colspec colnum="6" colname="b05" align="center" /> + <colspec colnum="7" colname="b04" align="center" /> + <colspec colnum="8" colname="b03" align="center" /> + <colspec colnum="9" colname="b02" align="center" /> + <colspec colnum="10" colname="b01" align="center" /> + <colspec colnum="11" colname="b00" align="center" /> + + <spanspec namest="b07" nameend="b00" spanname="b0" /> + <spanspec namest="b17" nameend="b10" spanname="b1" /> + <spanspec namest="b27" nameend="b20" spanname="b2" /> + <spanspec namest="b37" nameend="b30" spanname="b3" /> + <thead> + <row> + <entry>Identifier</entry> + <entry>Code</entry> + <entry> </entry> + <entry spanname="b0">Byte 0</entry> + </row> + <row> + <entry> </entry> + <entry> </entry> + <entry>Bit</entry> + <entry>7</entry> + <entry>6</entry> + <entry>5</entry> + <entry>4</entry> + <entry>3</entry> + <entry>2</entry> + <entry>1</entry> + <entry>0</entry> + </row> + </thead> + <tbody valign="top"> + <row id="V4L2-PIX-FMT-PAL8"> + <entry><constant>V4L2_PIX_FMT_PAL8</constant></entry> + <entry>'PAL8'</entry> + <entry></entry> + <entry>i<subscript>7</subscript></entry> + <entry>i<subscript>6</subscript></entry> + <entry>i<subscript>5</subscript></entry> + <entry>i<subscript>4</subscript></entry> + <entry>i<subscript>3</subscript></entry> + <entry>i<subscript>2</subscript></entry> + <entry>i<subscript>1</subscript></entry> + <entry>i<subscript>0</subscript></entry> + </row> + </tbody> + </tgroup> + </table> + </section> + + <section id="pixfmt-rgb"> + <title>RGB Formats</title> + + &sub-packed-rgb; + &sub-sbggr8; + &sub-sgbrg8; + &sub-sgrbg8; + &sub-srggb8; + &sub-sbggr16; + &sub-srggb10; + &sub-srggb10p; + &sub-srggb10alaw8; + &sub-srggb10dpcm8; + &sub-srggb12; + </section> + + <section id="yuv-formats"> + <title>YUV Formats</title> + + <para>YUV is the format native to TV broadcast and composite video +signals. It separates the brightness information (Y) from the color +information (U and V or Cb and Cr). The color information consists of +red and blue <emphasis>color difference</emphasis> signals, this way +the green component can be reconstructed by subtracting from the +brightness component. See <xref linkend="colorspaces" /> for conversion +examples. YUV was chosen because early television would only transmit +brightness information. To add color in a way compatible with existing +receivers a new signal carrier was added to transmit the color +difference signals. Secondary in the YUV format the U and V components +usually have lower resolution than the Y component. This is an analog +video compression technique taking advantage of a property of the +human visual system, being more sensitive to brightness +information.</para> + + &sub-packed-yuv; + &sub-grey; + &sub-y10; + &sub-y12; + &sub-y10b; + &sub-y16; + &sub-uv8; + &sub-yuyv; + &sub-uyvy; + &sub-yvyu; + &sub-vyuy; + &sub-y41p; + &sub-yuv420; + &sub-yuv420m; + &sub-yvu420m; + &sub-yuv410; + &sub-yuv422p; + &sub-yuv411p; + &sub-nv12; + &sub-nv12m; + &sub-nv12mt; + &sub-nv16; + &sub-nv16m; + &sub-nv24; + &sub-m420; + </section> + + <section> + <title>Compressed Formats</title> + + <table pgwide="1" frame="none" id="compressed-formats"> + <title>Compressed Image Formats</title> + <tgroup cols="3" align="left"> + &cs-def; + <thead> + <row> + <entry>Identifier</entry> + <entry>Code</entry> + <entry>Details</entry> + </row> + </thead> + <tbody valign="top"> + <row id="V4L2-PIX-FMT-JPEG"> + <entry><constant>V4L2_PIX_FMT_JPEG</constant></entry> + <entry>'JPEG'</entry> + <entry>TBD. See also &VIDIOC-G-JPEGCOMP;, + &VIDIOC-S-JPEGCOMP;.</entry> + </row> + <row id="V4L2-PIX-FMT-MPEG"> + <entry><constant>V4L2_PIX_FMT_MPEG</constant></entry> + <entry>'MPEG'</entry> + <entry>MPEG multiplexed stream. The actual format is determined by +extended control <constant>V4L2_CID_MPEG_STREAM_TYPE</constant>, see +<xref linkend="mpeg-control-id" />.</entry> + </row> + <row id="V4L2-PIX-FMT-H264"> + <entry><constant>V4L2_PIX_FMT_H264</constant></entry> + <entry>'H264'</entry> + <entry>H264 video elementary stream with start codes.</entry> + </row> + <row id="V4L2-PIX-FMT-H264-NO-SC"> + <entry><constant>V4L2_PIX_FMT_H264_NO_SC</constant></entry> + <entry>'AVC1'</entry> + <entry>H264 video elementary stream without start codes.</entry> + </row> + <row id="V4L2-PIX-FMT-H264-MVC"> + <entry><constant>V4L2_PIX_FMT_H264_MVC</constant></entry> + <entry>'M264'</entry> + <entry>H264 MVC video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-H263"> + <entry><constant>V4L2_PIX_FMT_H263</constant></entry> + <entry>'H263'</entry> + <entry>H263 video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-MPEG1"> + <entry><constant>V4L2_PIX_FMT_MPEG1</constant></entry> + <entry>'MPG1'</entry> + <entry>MPEG1 video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-MPEG2"> + <entry><constant>V4L2_PIX_FMT_MPEG2</constant></entry> + <entry>'MPG2'</entry> + <entry>MPEG2 video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-MPEG4"> + <entry><constant>V4L2_PIX_FMT_MPEG4</constant></entry> + <entry>'MPG4'</entry> + <entry>MPEG4 video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-XVID"> + <entry><constant>V4L2_PIX_FMT_XVID</constant></entry> + <entry>'XVID'</entry> + <entry>Xvid video elementary stream.</entry> + </row> + <row id="V4L2-PIX-FMT-VC1-ANNEX-G"> + <entry><constant>V4L2_PIX_FMT_VC1_ANNEX_G</constant></entry> + <entry>'VC1G'</entry> + <entry>VC1, SMPTE 421M Annex G compliant stream.</entry> + </row> + <row id="V4L2-PIX-FMT-VC1-ANNEX-L"> + <entry><constant>V4L2_PIX_FMT_VC1_ANNEX_L</constant></entry> + <entry>'VC1L'</entry> + <entry>VC1, SMPTE 421M Annex L compliant stream.</entry> + </row> + <row id="V4L2-PIX-FMT-VP8"> + <entry><constant>V4L2_PIX_FMT_VP8</constant></entry> + <entry>'VP80'</entry> + <entry>VP8 video elementary stream.</entry> + </row> + </tbody> + </tgroup> + </table> + </section> + + <section id="sdr-formats"> + <title>SDR Formats</title> + + <para>These formats are used for <link linkend="sdr">SDR Capture</link> +interface only.</para> + + &sub-sdr-cu08; + &sub-sdr-cu16le; + &sub-sdr-cs08; + &sub-sdr-cs14le; + &sub-sdr-ru12le; + + </section> + + <section id="pixfmt-reserved"> + <title>Reserved Format Identifiers</title> + + <para>These formats are not defined by this specification, they +are just listed for reference and to avoid naming conflicts. If you +want to register your own format, send an e-mail to the linux-media mailing +list &v4l-ml; for inclusion in the <filename>videodev2.h</filename> +file. If you want to share your format with other developers add a +link to your documentation and send a copy to the linux-media mailing list +for inclusion in this section. If you think your format should be listed +in a standard format section please make a proposal on the linux-media mailing +list.</para> + + <table pgwide="1" frame="none" id="reserved-formats"> + <title>Reserved Image Formats</title> + <tgroup cols="3" align="left"> + &cs-def; + <thead> + <row> + <entry>Identifier</entry> + <entry>Code</entry> + <entry>Details</entry> + </row> + </thead> + <tbody valign="top"> + <row id="V4L2-PIX-FMT-DV"> + <entry><constant>V4L2_PIX_FMT_DV</constant></entry> + <entry>'dvsd'</entry> + <entry>unknown</entry> + </row> + <row id="V4L2-PIX-FMT-ET61X251"> + <entry><constant>V4L2_PIX_FMT_ET61X251</constant></entry> + <entry>'E625'</entry> + <entry>Compressed format of the ET61X251 driver.</entry> + </row> + <row id="V4L2-PIX-FMT-HI240"> + <entry><constant>V4L2_PIX_FMT_HI240</constant></entry> + <entry>'HI24'</entry> + <entry><para>8 bit RGB format used by the BTTV driver.</para></entry> + </row> + <row id="V4L2-PIX-FMT-HM12"> + <entry><constant>V4L2_PIX_FMT_HM12</constant></entry> + <entry>'HM12'</entry> + <entry><para>YUV 4:2:0 format used by the +IVTV driver, <ulink url="http://www.ivtvdriver.org/"> +http://www.ivtvdriver.org/</ulink></para><para>The format is documented in the +kernel sources in the file <filename>Documentation/video4linux/cx2341x/README.hm12</filename> +</para></entry> + </row> + <row id="V4L2-PIX-FMT-CPIA1"> + <entry><constant>V4L2_PIX_FMT_CPIA1</constant></entry> + <entry>'CPIA'</entry> + <entry>YUV format used by the gspca cpia1 driver.</entry> + </row> + <row id="V4L2-PIX-FMT-JPGL"> + <entry><constant>V4L2_PIX_FMT_JPGL</constant></entry> + <entry>'JPGL'</entry> + <entry>JPEG-Light format (Pegasus Lossless JPEG) + used in Divio webcams NW 80x.</entry> + </row> + <row id="V4L2-PIX-FMT-SPCA501"> + <entry><constant>V4L2_PIX_FMT_SPCA501</constant></entry> + <entry>'S501'</entry> + <entry>YUYV per line used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SPCA505"> + <entry><constant>V4L2_PIX_FMT_SPCA505</constant></entry> + <entry>'S505'</entry> + <entry>YYUV per line used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SPCA508"> + <entry><constant>V4L2_PIX_FMT_SPCA508</constant></entry> + <entry>'S508'</entry> + <entry>YUVY per line used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SPCA561"> + <entry><constant>V4L2_PIX_FMT_SPCA561</constant></entry> + <entry>'S561'</entry> + <entry>Compressed GBRG Bayer format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-PAC207"> + <entry><constant>V4L2_PIX_FMT_PAC207</constant></entry> + <entry>'P207'</entry> + <entry>Compressed BGGR Bayer format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-MR97310A"> + <entry><constant>V4L2_PIX_FMT_MR97310A</constant></entry> + <entry>'M310'</entry> + <entry>Compressed BGGR Bayer format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-JL2005BCD"> + <entry><constant>V4L2_PIX_FMT_JL2005BCD</constant></entry> + <entry>'JL20'</entry> + <entry>JPEG compressed RGGB Bayer format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-OV511"> + <entry><constant>V4L2_PIX_FMT_OV511</constant></entry> + <entry>'O511'</entry> + <entry>OV511 JPEG format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-OV518"> + <entry><constant>V4L2_PIX_FMT_OV518</constant></entry> + <entry>'O518'</entry> + <entry>OV518 JPEG format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-PJPG"> + <entry><constant>V4L2_PIX_FMT_PJPG</constant></entry> + <entry>'PJPG'</entry> + <entry>Pixart 73xx JPEG format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SE401"> + <entry><constant>V4L2_PIX_FMT_SE401</constant></entry> + <entry>'S401'</entry> + <entry>Compressed RGB format used by the gspca se401 driver</entry> + </row> + <row id="V4L2-PIX-FMT-SQ905C"> + <entry><constant>V4L2_PIX_FMT_SQ905C</constant></entry> + <entry>'905C'</entry> + <entry>Compressed RGGB bayer format used by the gspca driver.</entry> + </row> + <row id="V4L2-PIX-FMT-MJPEG"> + <entry><constant>V4L2_PIX_FMT_MJPEG</constant></entry> + <entry>'MJPG'</entry> + <entry>Compressed format used by the Zoran driver</entry> + </row> + <row id="V4L2-PIX-FMT-PWC1"> + <entry><constant>V4L2_PIX_FMT_PWC1</constant></entry> + <entry>'PWC1'</entry> + <entry>Compressed format of the PWC driver.</entry> + </row> + <row id="V4L2-PIX-FMT-PWC2"> + <entry><constant>V4L2_PIX_FMT_PWC2</constant></entry> + <entry>'PWC2'</entry> + <entry>Compressed format of the PWC driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SN9C10X"> + <entry><constant>V4L2_PIX_FMT_SN9C10X</constant></entry> + <entry>'S910'</entry> + <entry>Compressed format of the SN9C102 driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SN9C20X-I420"> + <entry><constant>V4L2_PIX_FMT_SN9C20X_I420</constant></entry> + <entry>'S920'</entry> + <entry>YUV 4:2:0 format of the gspca sn9c20x driver.</entry> + </row> + <row id="V4L2-PIX-FMT-SN9C2028"> + <entry><constant>V4L2_PIX_FMT_SN9C2028</constant></entry> + <entry>'SONX'</entry> + <entry>Compressed GBRG bayer format of the gspca sn9c2028 driver.</entry> + </row> + <row id="V4L2-PIX-FMT-STV0680"> + <entry><constant>V4L2_PIX_FMT_STV0680</constant></entry> + <entry>'S680'</entry> + <entry>Bayer format of the gspca stv0680 driver.</entry> + </row> + <row id="V4L2-PIX-FMT-WNVA"> + <entry><constant>V4L2_PIX_FMT_WNVA</constant></entry> + <entry>'WNVA'</entry> + <entry><para>Used by the Winnov Videum driver, <ulink +url="http://www.thedirks.org/winnov/"> +http://www.thedirks.org/winnov/</ulink></para></entry> + </row> + <row id="V4L2-PIX-FMT-TM6000"> + <entry><constant>V4L2_PIX_FMT_TM6000</constant></entry> + <entry>'TM60'</entry> + <entry><para>Used by Trident tm6000</para></entry> + </row> + <row id="V4L2-PIX-FMT-CIT-YYVYUY"> + <entry><constant>V4L2_PIX_FMT_CIT_YYVYUY</constant></entry> + <entry>'CITV'</entry> + <entry><para>Used by xirlink CIT, found at IBM webcams.</para> + <para>Uses one line of Y then 1 line of VYUY</para> + </entry> + </row> + <row id="V4L2-PIX-FMT-KONICA420"> + <entry><constant>V4L2_PIX_FMT_KONICA420</constant></entry> + <entry>'KONI'</entry> + <entry><para>Used by Konica webcams.</para> + <para>YUV420 planar in blocks of 256 pixels.</para> + </entry> + </row> + <row id="V4L2-PIX-FMT-YYUV"> + <entry><constant>V4L2_PIX_FMT_YYUV</constant></entry> + <entry>'YYUV'</entry> + <entry>unknown</entry> + </row> + <row id="V4L2-PIX-FMT-Y4"> + <entry><constant>V4L2_PIX_FMT_Y4</constant></entry> + <entry>'Y04 '</entry> + <entry>Old 4-bit greyscale format. Only the most significant 4 bits of each byte are used, +the other bits are set to 0.</entry> + </row> + <row id="V4L2-PIX-FMT-Y6"> + <entry><constant>V4L2_PIX_FMT_Y6</constant></entry> + <entry>'Y06 '</entry> + <entry>Old 6-bit greyscale format. Only the most significant 6 bits of each byte are used, +the other bits are set to 0.</entry> + </row> + <row id="V4L2-PIX-FMT-S5C-UYVY-JPG"> + <entry><constant>V4L2_PIX_FMT_S5C_UYVY_JPG</constant></entry> + <entry>'S5CI'</entry> + <entry>Two-planar format used by Samsung S5C73MX cameras. The +first plane contains interleaved JPEG and UYVY image data, followed by meta data +in form of an array of offsets to the UYVY data blocks. The actual pointer array +follows immediately the interleaved JPEG/UYVY data, the number of entries in +this array equals the height of the UYVY image. Each entry is a 4-byte unsigned +integer in big endian order and it's an offset to a single pixel line of the +UYVY image. The first plane can start either with JPEG or UYVY data chunk. The +size of a single UYVY block equals the UYVY image's width multiplied by 2. The +size of a JPEG chunk depends on the image and can vary with each line. +<para>The second plane, at an offset of 4084 bytes, contains a 4-byte offset to +the pointer array in the first plane. This offset is followed by a 4-byte value +indicating size of the pointer array. All numbers in the second plane are also +in big endian order. Remaining data in the second plane is undefined. The +information in the second plane allows to easily find location of the pointer +array, which can be different for each frame. The size of the pointer array is +constant for given UYVY image height.</para> +<para>In order to extract UYVY and JPEG frames an application can initially set +a data pointer to the start of first plane and then add an offset from the first +entry of the pointers table. Such a pointer indicates start of an UYVY image +pixel line. Whole UYVY line can be copied to a separate buffer. These steps +should be repeated for each line, i.e. the number of entries in the pointer +array. Anything what's in between the UYVY lines is JPEG data and should be +concatenated to form the JPEG stream. </para> +</entry> + </row> + </tbody> + </tgroup> + </table> + + <table frame="none" pgwide="1" id="format-flags"> + <title>Format Flags</title> + <tgroup cols="3"> + &cs-def; + <tbody valign="top"> + <row> + <entry><constant>V4L2_PIX_FMT_FLAG_PREMUL_ALPHA</constant></entry> + <entry>0x00000001</entry> + <entry>The color values are premultiplied by the alpha channel +value. For example, if a light blue pixel with 50% transparency was described by +RGBA values (128, 192, 255, 128), the same pixel described with premultiplied +colors would be described by RGBA values (64, 96, 128, 128) </entry> + </row> + </tbody> + </tgroup> + </table> + </section> |