diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-11 11:49:23 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-11 11:49:23 -0800 |
| commit | 2183a58803c2bbd87c2d0057eed6779ec4718d4d (patch) | |
| tree | 910860a2f0c1f22efe840428f11077a5bd478933 /Documentation | |
| parent | e28870f9b3e92cd3570925089c6bb789c2603bc4 (diff) | |
| parent | 71947828caef0c83d4245f7d1eaddc799b4ff1d1 (diff) | |
Merge tag 'media/v3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
Pull media updates from Mauro Carvalho Chehab:
- Two new dvb frontend drivers: mn88472 and mn88473
- A new driver for some PCIe DVBSky cards
- A new remote controller driver: meson-ir
- One LIRC staging driver got rewritten and promoted to mainstream:
igorplugusb
- A new tuner driver (m88rs6000t)
- The old omap2 media driver got removed from staging. This driver
uses an old DMA API and it is likely broken on recent kernels.
Nobody cared enough to fix it
- Media bus format moved to a separate header, as DRM will also use the
definitions there
- mem2mem_testdev were renamed to vim2m, in order to use the same
naming convention taken by the other virtual test driver (vivid)
- Added a new driver for coda SoC (coda-jpeg)
- The cx88 driver got converted to use videobuf2 core
- Make DMABUF export buffer to work with DMA Scatter/Gather and Vmalloc
cores
- Lots of other fixes, improvements and cleanups on the drivers.
* tag 'media/v3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (384 commits)
[media] mn88473: One function call less in mn88473_init() after error
[media] mn88473: Remove uneeded check before release_firmware()
[media] lirc_zilog: Deletion of unnecessary checks before vfree()
[media] MAINTAINERS: Add myself as img-ir maintainer
[media] img-ir: Don't set driver's module owner
[media] img-ir: Depend on METAG or MIPS or COMPILE_TEST
[media] img-ir/hw: Drop [un]register_decoder declarations
[media] img-ir/hw: Fix potential deadlock stopping timer
[media] img-ir/hw: Always read data to clear buffer
[media] redrat3: ensure dma is setup properly
[media] ddbridge: remove unneeded check before dvb_unregister_device()
[media] si2157: One function call less in si2157_init() after error
[media] tuners: remove uneeded checks before release_firmware()
[media] arm: omap2: rx51-peripherals: fix build warning
[media] stv090x: add an extra protetion against buffer overflow
[media] stv090x: Remove an unreachable code
[media] stv090x: Some whitespace cleanups
[media] em28xx: checkpatch cleanup: whitespaces/new lines cleanups
[media] si2168: add support for firmware files in new format
[media] si2168: debug printout for firmware version
...
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/media/dvb/dvbproperty.xml | 4 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/biblio.xml | 85 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/dev-subdev.xml | 109 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/io.xml | 5 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/pixfmt.xml | 1274 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/selections-common.xml | 16 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/subdev-formats.xml | 308 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-enuminput.xml | 8 | ||||
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-enumoutput.xml | 8 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/media/meson-ir.txt | 14 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/media/si4713.txt | 30 | ||||
| -rw-r--r-- | Documentation/video4linux/CARDLIST.cx23885 | 2 | ||||
| -rw-r--r-- | Documentation/video4linux/CARDLIST.em28xx | 1 | ||||
| -rw-r--r-- | Documentation/video4linux/CARDLIST.saa7134 | 1 | ||||
| -rw-r--r-- | Documentation/video4linux/soc-camera.txt | 2 |
15 files changed, 1356 insertions, 511 deletions
diff --git a/Documentation/DocBook/media/dvb/dvbproperty.xml b/Documentation/DocBook/media/dvb/dvbproperty.xml index 948ddaab592e..3018564ddfd9 100644 --- a/Documentation/DocBook/media/dvb/dvbproperty.xml +++ b/Documentation/DocBook/media/dvb/dvbproperty.xml @@ -120,8 +120,8 @@ struct dtv_properties { </para> <informaltable><tgroup cols="1"><tbody><row><entry align="char"> -<para>This ioctl call sets one or more frontend properties. This call only - requires read-only access to the device.</para> +<para>This ioctl call sets one or more frontend properties. This call + requires read/write access to the device.</para> </entry> </row></tbody></tgroup></informaltable> <para>SYNOPSIS diff --git a/Documentation/DocBook/media/v4l/biblio.xml b/Documentation/DocBook/media/v4l/biblio.xml index d2eb79e41a01..7ff01a23c2fe 100644 --- a/Documentation/DocBook/media/v4l/biblio.xml +++ b/Documentation/DocBook/media/v4l/biblio.xml @@ -178,6 +178,75 @@ Signal - NTSC for Studio Applications"</title> 1125-Line High-Definition Production"</title> </biblioentry> + <biblioentry id="srgb"> + <abbrev>sRGB</abbrev> + <authorgroup> + <corpauthor>International Electrotechnical Commission +(<ulink url="http://www.iec.ch">http://www.iec.ch</ulink>)</corpauthor> + </authorgroup> + <title>IEC 61966-2-1 ed1.0 "Multimedia systems and equipment - Colour measurement +and management - Part 2-1: Colour management - Default RGB colour space - sRGB"</title> + </biblioentry> + + <biblioentry id="sycc"> + <abbrev>sYCC</abbrev> + <authorgroup> + <corpauthor>International Electrotechnical Commission +(<ulink url="http://www.iec.ch">http://www.iec.ch</ulink>)</corpauthor> + </authorgroup> + <title>IEC 61966-2-1-am1 ed1.0 "Amendment 1 - Multimedia systems and equipment - Colour measurement +and management - Part 2-1: Colour management - Default RGB colour space - sRGB"</title> + </biblioentry> + + <biblioentry id="xvycc"> + <abbrev>xvYCC</abbrev> + <authorgroup> + <corpauthor>International Electrotechnical Commission +(<ulink url="http://www.iec.ch">http://www.iec.ch</ulink>)</corpauthor> + </authorgroup> + <title>IEC 61966-2-4 ed1.0 "Multimedia systems and equipment - Colour measurement +and management - Part 2-4: Colour management - Extended-gamut YCC colour space for video +applications - xvYCC"</title> + </biblioentry> + + <biblioentry id="adobergb"> + <abbrev>AdobeRGB</abbrev> + <authorgroup> + <corpauthor>Adobe Systems Incorporated (<ulink url="http://www.adobe.com">http://www.adobe.com</ulink>)</corpauthor> + </authorgroup> + <title>Adobe© RGB (1998) Color Image Encoding Version 2005-05</title> + </biblioentry> + + <biblioentry id="oprgb"> + <abbrev>opRGB</abbrev> + <authorgroup> + <corpauthor>International Electrotechnical Commission +(<ulink url="http://www.iec.ch">http://www.iec.ch</ulink>)</corpauthor> + </authorgroup> + <title>IEC 61966-2-5 "Multimedia systems and equipment - Colour measurement +and management - Part 2-5: Colour management - Optional RGB colour space - opRGB"</title> + </biblioentry> + + <biblioentry id="itu2020"> + <abbrev>ITU BT.2020</abbrev> + <authorgroup> + <corpauthor>International Telecommunication Union (<ulink +url="http://www.itu.ch">http://www.itu.ch</ulink>)</corpauthor> + </authorgroup> + <title>ITU-R Recommendation BT.2020 (08/2012) "Parameter values for ultra-high +definition television systems for production and international programme exchange" +</title> + </biblioentry> + + <biblioentry id="tech3213"> + <abbrev>EBU Tech 3213</abbrev> + <authorgroup> + <corpauthor>European Broadcast Union (<ulink +url="http://www.ebu.ch">http://www.ebu.ch</ulink>)</corpauthor> + </authorgroup> + <title>E.B.U. Standard for Chromaticity Tolerances for Studio Monitors"</title> + </biblioentry> + <biblioentry id="iec62106"> <abbrev>IEC 62106</abbrev> <authorgroup> @@ -266,4 +335,20 @@ in the frequency range from 87,5 to 108,0 MHz</title> <subtitle>Version 1, Revision 2</subtitle> </biblioentry> + <biblioentry id="poynton"> + <abbrev>poynton</abbrev> + <authorgroup> + <corpauthor>Charles Poynton</corpauthor> + </authorgroup> + <title>Digital Video and HDTV, Algorithms and Interfaces</title> + </biblioentry> + + <biblioentry id="colimg"> + <abbrev>colimg</abbrev> + <authorgroup> + <corpauthor>Erik Reinhard et al.</corpauthor> + </authorgroup> + <title>Color Imaging: Fundamentals and Applications</title> + </biblioentry> + </bibliography> diff --git a/Documentation/DocBook/media/v4l/dev-subdev.xml b/Documentation/DocBook/media/v4l/dev-subdev.xml index d15aaf83f56f..4f0ba58c9bd9 100644 --- a/Documentation/DocBook/media/v4l/dev-subdev.xml +++ b/Documentation/DocBook/media/v4l/dev-subdev.xml @@ -195,53 +195,59 @@ <title>Sample Pipeline Configuration</title> <tgroup cols="3"> <colspec colname="what"/> - <colspec colname="sensor-0" /> - <colspec colname="frontend-0" /> - <colspec colname="frontend-1" /> - <colspec colname="scaler-0" /> - <colspec colname="scaler-1" /> + <colspec colname="sensor-0 format" /> + <colspec colname="frontend-0 format" /> + <colspec colname="frontend-1 format" /> + <colspec colname="scaler-0 format" /> + <colspec colname="scaler-0 compose" /> + <colspec colname="scaler-1 format" /> <thead> <row> <entry></entry> - <entry>Sensor/0</entry> - <entry>Frontend/0</entry> - <entry>Frontend/1</entry> - <entry>Scaler/0</entry> - <entry>Scaler/1</entry> + <entry>Sensor/0 format</entry> + <entry>Frontend/0 format</entry> + <entry>Frontend/1 format</entry> + <entry>Scaler/0 format</entry> + <entry>Scaler/0 compose selection rectangle</entry> + <entry>Scaler/1 format</entry> </row> </thead> <tbody valign="top"> <row> <entry>Initial state</entry> - <entry>2048x1536</entry> - <entry>-</entry> - <entry>-</entry> - <entry>-</entry> - <entry>-</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry>(default)</entry> + <entry>(default)</entry> + <entry>(default)</entry> + <entry>(default)</entry> + <entry>(default)</entry> </row> <row> - <entry>Configure frontend input</entry> - <entry>2048x1536</entry> - <entry><emphasis>2048x1536</emphasis></entry> - <entry><emphasis>2046x1534</emphasis></entry> - <entry>-</entry> - <entry>-</entry> + <entry>Configure frontend sink format</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry><emphasis>2048x1536/SGRBG8_1X8</emphasis></entry> + <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> + <entry>(default)</entry> + <entry>(default)</entry> + <entry>(default)</entry> </row> <row> - <entry>Configure scaler input</entry> - <entry>2048x1536</entry> - <entry>2048x1536</entry> - <entry>2046x1534</entry> - <entry><emphasis>2046x1534</emphasis></entry> - <entry><emphasis>2046x1534</emphasis></entry> + <entry>Configure scaler sink format</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry>2046x1534/SGRBG8_1X8</entry> + <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> + <entry><emphasis>0,0/2046x1534</emphasis></entry> + <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> </row> <row> - <entry>Configure scaler output</entry> - <entry>2048x1536</entry> - <entry>2048x1536</entry> - <entry>2046x1534</entry> - <entry>2046x1534</entry> - <entry><emphasis>1280x960</emphasis></entry> + <entry>Configure scaler sink compose selection</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry>2048x1536/SGRBG8_1X8</entry> + <entry>2046x1534/SGRBG8_1X8</entry> + <entry>2046x1534/SGRBG8_1X8</entry> + <entry><emphasis>0,0/1280x960</emphasis></entry> + <entry><emphasis>1280x960/SGRBG8_1X8</emphasis></entry> </row> </tbody> </tgroup> @@ -249,19 +255,30 @@ <para> <orderedlist> - <listitem><para>Initial state. The sensor output is set to its native 3MP - resolution. Resolutions on the host frontend and scaler input and output - pads are undefined.</para></listitem> - <listitem><para>The application configures the frontend input pad resolution to - 2048x1536. The driver propagates the format to the frontend output pad. - Note that the propagated output format can be different, as in this case, - than the input format, as the hardware might need to crop pixels (for - instance when converting a Bayer filter pattern to RGB or YUV).</para></listitem> - <listitem><para>The application configures the scaler input pad resolution to - 2046x1534 to match the frontend output resolution. The driver propagates - the format to the scaler output pad.</para></listitem> - <listitem><para>The application configures the scaler output pad resolution to - 1280x960.</para></listitem> + <listitem><para>Initial state. The sensor source pad format is + set to its native 3MP size and V4L2_MBUS_FMT_SGRBG8_1X8 + media bus code. Formats on the host frontend and scaler sink + and source pads have the default values, as well as the + compose rectangle on the scaler's sink pad.</para></listitem> + + <listitem><para>The application configures the frontend sink + pad format's size to 2048x1536 and its media bus code to + V4L2_MBUS_FMT_SGRBG_1X8. The driver propagates the format to + the frontend source pad.</para></listitem> + + <listitem><para>The application configures the scaler sink pad + format's size to 2046x1534 and the media bus code to + V4L2_MBUS_FMT_SGRBG_1X8 to match the frontend source size and + media bus code. The media bus code on the sink pad is set to + V4L2_MBUS_FMT_SGRBG_1X8. The driver propagates the size to the + compose selection rectangle on the scaler's sink pad, and the + format to the scaler source pad.</para></listitem> + + <listitem><para>The application configures the size of the compose + selection rectangle of the scaler's sink pad 1280x960. The driver + propagates the size to the scaler's source pad + format.</para></listitem> + </orderedlist> </para> diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index e5e8325aa3d7..1c17f802b471 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -1422,7 +1422,10 @@ one of the <constant>V4L2_FIELD_NONE</constant>, <constant>V4L2_FIELD_BOTTOM</constant>, or <constant>V4L2_FIELD_INTERLACED</constant> formats is acceptable. Drivers choose depending on hardware capabilities or e. g. the -requested image size, and return the actual field order. &v4l2-buffer; +requested image size, and return the actual field order. Drivers must +never return <constant>V4L2_FIELD_ANY</constant>. If multiple +field orders are possible the driver must choose one of the possible +field orders during &VIDIOC-S-FMT; or &VIDIOC-TRY-FMT;. &v4l2-buffer; <structfield>field</structfield> can never be <constant>V4L2_FIELD_ANY</constant>.</entry> </row> diff --git a/Documentation/DocBook/media/v4l/pixfmt.xml b/Documentation/DocBook/media/v4l/pixfmt.xml index df5b23d46552..ccf6053c1ae4 100644 --- a/Documentation/DocBook/media/v4l/pixfmt.xml +++ b/Documentation/DocBook/media/v4l/pixfmt.xml @@ -296,343 +296,1003 @@ in the 2-planar version or with each component in its own buffer in the <section id="colorspaces"> <title>Colorspaces</title> - <para>[intro]</para> + <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> - <!-- See proposal by Billy Biggs, video4linux-list@redhat.com -on 11 Oct 2002, subject: "Re: [V4L] Re: v4l2 api", and -http://vektor.theorem.ca/graphics/ycbcr/ and -http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html --> + <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> - <variablelist> - <varlistentry> - <term>Gamma Correction</term> - <listitem> - <para>[to do]</para> - <para>E'<subscript>R</subscript> = f(R)</para> - <para>E'<subscript>G</subscript> = f(G)</para> - <para>E'<subscript>B</subscript> = f(B)</para> - </listitem> - </varlistentry> - <varlistentry> - <term>Construction of luminance and color-difference -signals</term> - <listitem> - <para>[to do]</para> - <para>E'<subscript>Y</subscript> = -Coeff<subscript>R</subscript> E'<subscript>R</subscript> -+ Coeff<subscript>G</subscript> E'<subscript>G</subscript> -+ Coeff<subscript>B</subscript> E'<subscript>B</subscript></para> - <para>(E'<subscript>R</subscript> - E'<subscript>Y</subscript>) = E'<subscript>R</subscript> -- Coeff<subscript>R</subscript> E'<subscript>R</subscript> -- Coeff<subscript>G</subscript> E'<subscript>G</subscript> -- Coeff<subscript>B</subscript> E'<subscript>B</subscript></para> - <para>(E'<subscript>B</subscript> - E'<subscript>Y</subscript>) = E'<subscript>B</subscript> -- Coeff<subscript>R</subscript> E'<subscript>R</subscript> -- Coeff<subscript>G</subscript> E'<subscript>G</subscript> -- Coeff<subscript>B</subscript> E'<subscript>B</subscript></para> - </listitem> - </varlistentry> - <varlistentry> - <term>Re-normalized color-difference signals</term> - <listitem> - <para>The color-difference signals are scaled back to unity -range [-0.5;+0.5]:</para> - <para>K<subscript>B</subscript> = 0.5 / (1 - Coeff<subscript>B</subscript>)</para> - <para>K<subscript>R</subscript> = 0.5 / (1 - Coeff<subscript>R</subscript>)</para> - <para>P<subscript>B</subscript> = -K<subscript>B</subscript> (E'<subscript>B</subscript> - E'<subscript>Y</subscript>) = - 0.5 (Coeff<subscript>R</subscript> / Coeff<subscript>B</subscript>) E'<subscript>R</subscript> -+ 0.5 (Coeff<subscript>G</subscript> / Coeff<subscript>B</subscript>) E'<subscript>G</subscript> -+ 0.5 E'<subscript>B</subscript></para> - <para>P<subscript>R</subscript> = -K<subscript>R</subscript> (E'<subscript>R</subscript> - E'<subscript>Y</subscript>) = - 0.5 E'<subscript>R</subscript> -+ 0.5 (Coeff<subscript>G</subscript> / Coeff<subscript>R</subscript>) E'<subscript>G</subscript> -+ 0.5 (Coeff<subscript>B</subscript> / Coeff<subscript>R</subscript>) E'<subscript>B</subscript></para> - </listitem> - </varlistentry> - <varlistentry> - <term>Quantization</term> - <listitem> - <para>[to do]</para> - <para>Y' = (Lum. Levels - 1) · E'<subscript>Y</subscript> + Lum. Offset</para> - <para>C<subscript>B</subscript> = (Chrom. Levels - 1) -· P<subscript>B</subscript> + Chrom. Offset</para> - <para>C<subscript>R</subscript> = (Chrom. Levels - 1) -· P<subscript>R</subscript> + Chrom. Offset</para> - <para>Rounding to the nearest integer and clamping to the range -[0;255] finally yields the digital color components Y'CbCr -stored in YUV images.</para> - </listitem> - </varlistentry> - </variablelist> - </para> - - <example> - <title>ITU-R Rec. BT.601 color conversion</title> - - <para>Forward Transformation</para> - - <programlisting> -int ER, EG, EB; /* gamma corrected RGB input [0;255] */ -int Y1, Cb, Cr; /* output [0;255] */ - -double r, g, b; /* temporaries */ -double y1, pb, pr; - -int -clamp (double x) -{ - int r = x; /* round to nearest */ - - if (r < 0) return 0; - else if (r > 255) return 255; - else return r; -} - -r = ER / 255.0; -g = EG / 255.0; -b = EB / 255.0; - -y1 = 0.299 * r + 0.587 * g + 0.114 * b; -pb = -0.169 * r - 0.331 * g + 0.5 * b; -pr = 0.5 * r - 0.419 * g - 0.081 * b; - -Y1 = clamp (219 * y1 + 16); -Cb = clamp (224 * pb + 128); -Cr = clamp (224 * pr + 128); - -/* or shorter */ - -y1 = 0.299 * ER + 0.587 * EG + 0.114 * EB; - -Y1 = clamp ( (219 / 255.0) * y1 + 16); -Cb = clamp (((224 / 255.0) / (2 - 2 * 0.114)) * (EB - y1) + 128); -Cr = clamp (((224 / 255.0) / (2 - 2 * 0.299)) * (ER - y1) + 128); - </programlisting> - - <para>Inverse Transformation</para> - - <programlisting> -int Y1, Cb, Cr; /* gamma pre-corrected input [0;255] */ -int ER, EG, EB; /* output [0;255] */ - -double r, g, b; /* temporaries */ -double y1, pb, pr; - -int -clamp (double x) -{ - int r = x; /* round to nearest */ - - if (r < 0) return 0; - else if (r > 255) return 255; - else return r; -} - -y1 = (Y1 - 16) / 219.0; -pb = (Cb - 128) / 224.0; -pr = (Cr - 128) / 224.0; - -r = 1.0 * y1 + 0 * pb + 1.402 * pr; -g = 1.0 * y1 - 0.344 * pb - 0.714 * pr; -b = 1.0 * y1 + 1.772 * pb + 0 * pr; - -ER = clamp (r * 255); /* [ok? one should prob. limit y1,pb,pr] */ -EG = clamp (g * 255); -EB = clamp (b * 255); - </programlisting> - </example> - - <table pgwide="1" id="v4l2-colorspace" orient="land"> - <title>enum v4l2_colorspace</title> - <tgroup cols="11" align="center"> - <colspec align="left" /> - <colspec align="center" /> - <colspec align="left" /> - <colspec colname="cr" /> - <colspec colname="cg" /> - <colspec colname="cb" /> - <colspec colname="wp" /> - <colspec colname="gc" /> - <colspec colname="lum" /> - <colspec colname="qy" /> - <colspec colname="qc" /> - <spanspec namest="cr" nameend="cb" spanname="chrom" /> - <spanspec namest="qy" nameend="qc" spanname="quant" /> - <spanspec namest="lum" nameend="qc" spanname="spam" /> + <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 always full range for all colorspaces, +so this won't be mentioned explicitly for each colorspace description.</para> + + <table pgwide="1" frame="none" id="v4l2-colorspace"> + <title>V4L2 Colorspaces</title> + <tgroup cols="2" align="left"> + &cs-def; <thead> <row> - <entry morerows="1">Identifier</entry> - <entry morerows="1">Value</entry> - <entry morerows="1">Description</entry> - <entry spanname="chrom">Chromaticities<footnote> - <para>The coordinates of the color primaries are -given in the CIE system (1931)</para> - </footnote></entry> - <entry morerows="1">White Point</entry> - <entry morerows="1">Gamma Correction</entry> - <entry morerows="1">Luminance E'<subscript>Y</subscript></entry> - <entry spanname="quant">Quantization</entry> - </row> - <row> - <entry>Red</entry> - <entry>Green</entry> - <entry>Blue</entry> - <entry>Y'</entry> - <entry>Cb, Cr</entry> + <entry>Identifier</entry> + <entry>Details</entry> </row> </thead> <tbody valign="top"> <row> <entry><constant>V4L2_COLORSPACE_SMPTE170M</constant></entry> - <entry>1</entry> - <entry>NTSC/PAL according to <xref linkend="smpte170m" />, -<xref linkend="itu601" /></entry> - <entry>x = 0.630, y = 0.340</entry> - <entry>x = 0.310, y = 0.595</entry> - <entry>x = 0.155, y = 0.070</entry> - <entry>x = 0.3127, y = 0.3290, - Illuminant D<subscript>65</subscript></entry> - <entry>E' = 4.5 I for I ≤0.018, -1.099 I<superscript>0.45</superscript> - 0.099 for 0.018 < I</entry> - <entry>0.299 E'<subscript>R</subscript> -+ 0.587 E'<subscript>G</subscript> -+ 0.114 E'<subscript>B</subscript></entry> - <entry>219 E'<subscript>Y</subscript> + 16</entry> - <entry>224 P<subscript>B,R</subscript> + 128</entry> + <entry>See <xref linkend="col-smpte-170m" />.</entry> </row> <row> - <entry><constant>V4L2_COLORSPACE_SMPTE240M</constant></entry> - <entry>2</entry> - <entry>1125-Line (US) HDTV, see <xref -linkend="smpte240m" /></entry> - <entry>x = 0.630, y = 0.340</entry> - <entry>x = 0.310, y = 0.595</entry> - |