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docs/formats.md

+# Introduction
+
+Formats (FOURCC) supported by libyuv are detailed here.
+
+# Core Formats
+
+There are 2 core formats supported by libyuv - I420 and ARGB.  All YUV formats can be converted to/from I420.  All RGB formats can be converted to/from ARGB.
+
+Filtering functions such as scaling and planar functions work on I420 and/or ARGB.
+
+# OSX Core Media Pixel Formats
+
+This is how OSX formats map to libyuv
+
+    enum {
+      kCMPixelFormat_32ARGB          = 32,      FOURCC_BGRA
+      kCMPixelFormat_32BGRA          = 'BGRA',  FOURCC_ARGB
+      kCMPixelFormat_24RGB           = 24,      FOURCC_RAW
+      kCMPixelFormat_16BE555         = 16,      Not supported.
+      kCMPixelFormat_16BE565         = 'B565',  Not supported.
+      kCMPixelFormat_16LE555         = 'L555',  FOURCC_RGBO
+      kCMPixelFormat_16LE565         = 'L565',  FOURCC_RGBP
+      kCMPixelFormat_16LE5551        = '5551',  FOURCC_RGBO
+      kCMPixelFormat_422YpCbCr8      = '2vuy',  FOURCC_UYVY
+      kCMPixelFormat_422YpCbCr8_yuvs = 'yuvs',  FOURCC_YUY2
+      kCMPixelFormat_444YpCbCr8      = 'v308',  FOURCC_I444 ?
+      kCMPixelFormat_4444YpCbCrA8    = 'v408',  Not supported.
+      kCMPixelFormat_422YpCbCr16     = 'v216',  Not supported.
+      kCMPixelFormat_422YpCbCr10     = 'v210',  FOURCC_V210 previously.  Removed now.
+      kCMPixelFormat_444YpCbCr10     = 'v410',  Not supported.
+      kCMPixelFormat_8IndexedGray_WhiteIsZero = 0x00000028,  Not supported.
+    };
+
+
+# FOURCC (Four Charactacter Code) List
+
+The following is extracted from video_common.h as a complete list of formats supported by libyuv.
+
+    enum FourCC {
+      // 9 Primary YUV formats: 5 planar, 2 biplanar, 2 packed.
+      FOURCC_I420 = FOURCC('I', '4', '2', '0'),
+      FOURCC_I422 = FOURCC('I', '4', '2', '2'),
+      FOURCC_I444 = FOURCC('I', '4', '4', '4'),
+      FOURCC_I411 = FOURCC('I', '4', '1', '1'),
+      FOURCC_I400 = FOURCC('I', '4', '0', '0'),
+      FOURCC_NV21 = FOURCC('N', 'V', '2', '1'),
+      FOURCC_NV12 = FOURCC('N', 'V', '1', '2'),
+      FOURCC_YUY2 = FOURCC('Y', 'U', 'Y', '2'),
+      FOURCC_UYVY = FOURCC('U', 'Y', 'V', 'Y'),
+
+      // 2 Secondary YUV formats: row biplanar.
+      FOURCC_M420 = FOURCC('M', '4', '2', '0'),
+      FOURCC_Q420 = FOURCC('Q', '4', '2', '0'),
+
+      // 9 Primary RGB formats: 4 32 bpp, 2 24 bpp, 3 16 bpp.
+      FOURCC_ARGB = FOURCC('A', 'R', 'G', 'B'),
+      FOURCC_BGRA = FOURCC('B', 'G', 'R', 'A'),
+      FOURCC_ABGR = FOURCC('A', 'B', 'G', 'R'),
+      FOURCC_24BG = FOURCC('2', '4', 'B', 'G'),
+      FOURCC_RAW  = FOURCC('r', 'a', 'w', ' '),
+      FOURCC_RGBA = FOURCC('R', 'G', 'B', 'A'),
+      FOURCC_RGBP = FOURCC('R', 'G', 'B', 'P'),  // rgb565 LE.
+      FOURCC_RGBO = FOURCC('R', 'G', 'B', 'O'),  // argb1555 LE.
+      FOURCC_R444 = FOURCC('R', '4', '4', '4'),  // argb4444 LE.
+
+      // 4 Secondary RGB formats: 4 Bayer Patterns.
+      FOURCC_RGGB = FOURCC('R', 'G', 'G', 'B'),
+      FOURCC_BGGR = FOURCC('B', 'G', 'G', 'R'),
+      FOURCC_GRBG = FOURCC('G', 'R', 'B', 'G'),
+      FOURCC_GBRG = FOURCC('G', 'B', 'R', 'G'),
+
+      // 1 Primary Compressed YUV format.
+      FOURCC_MJPG = FOURCC('M', 'J', 'P', 'G'),
+
+      // 5 Auxiliary YUV variations: 3 with U and V planes are swapped, 1 Alias.
+      FOURCC_YV12 = FOURCC('Y', 'V', '1', '2'),
+      FOURCC_YV16 = FOURCC('Y', 'V', '1', '6'),
+      FOURCC_YV24 = FOURCC('Y', 'V', '2', '4'),
+      FOURCC_YU12 = FOURCC('Y', 'U', '1', '2'),  // Linux version of I420.
+      FOURCC_J420 = FOURCC('J', '4', '2', '0'),
+      FOURCC_J400 = FOURCC('J', '4', '0', '0'),
+
+      // 14 Auxiliary aliases.  CanonicalFourCC() maps these to canonical fourcc.
+      FOURCC_IYUV = FOURCC('I', 'Y', 'U', 'V'),  // Alias for I420.
+      FOURCC_YU16 = FOURCC('Y', 'U', '1', '6'),  // Alias for I422.
+      FOURCC_YU24 = FOURCC('Y', 'U', '2', '4'),  // Alias for I444.
+      FOURCC_YUYV = FOURCC('Y', 'U', 'Y', 'V'),  // Alias for YUY2.
+      FOURCC_YUVS = FOURCC('y', 'u', 'v', 's'),  // Alias for YUY2 on Mac.
+      FOURCC_HDYC = FOURCC('H', 'D', 'Y', 'C'),  // Alias for UYVY.
+      FOURCC_2VUY = FOURCC('2', 'v', 'u', 'y'),  // Alias for UYVY on Mac.
+      FOURCC_JPEG = FOURCC('J', 'P', 'E', 'G'),  // Alias for MJPG.
+      FOURCC_DMB1 = FOURCC('d', 'm', 'b', '1'),  // Alias for MJPG on Mac.
+      FOURCC_BA81 = FOURCC('B', 'A', '8', '1'),  // Alias for BGGR.
+      FOURCC_RGB3 = FOURCC('R', 'G', 'B', '3'),  // Alias for RAW.
+      FOURCC_BGR3 = FOURCC('B', 'G', 'R', '3'),  // Alias for 24BG.
+      FOURCC_CM32 = FOURCC(0, 0, 0, 32),  // Alias for BGRA kCMPixelFormat_32ARGB
+      FOURCC_CM24 = FOURCC(0, 0, 0, 24),  // Alias for RAW kCMPixelFormat_24RGB
+      FOURCC_L555 = FOURCC('L', '5', '5', '5'),  // Alias for RGBO.
+      FOURCC_L565 = FOURCC('L', '5', '6', '5'),  // Alias for RGBP.
+      FOURCC_5551 = FOURCC('5', '5', '5', '1'),  // Alias for RGBO.
+
+      // 1 Auxiliary compressed YUV format set aside for capturer.
+      FOURCC_H264 = FOURCC('H', '2', '6', '4'),
+
+# The ARGB FOURCC
+
+There are 4 ARGB layouts - ARGB, BGRA, ABGR and RGBA.  ARGB is most common by far, used for screen formats, and windows webcam drivers.
+
+The fourcc describes the order of channels in a ***register***.
+
+A fourcc provided by capturer, can be thought of string, e.g. "ARGB".
+
+On little endian machines, as an int, this would have 'A' in the lowest byte.  The FOURCC macro reverses the order:
+
+    #define FOURCC(a, b, c, d) (((uint32)(a)) | ((uint32)(b) << 8) | ((uint32)(c) << 16) | ((uint32)(d) << 24))
+
+So the "ARGB" string, read as an uint32, is
+
+    FOURCC_ARGB = FOURCC('A', 'R', 'G', 'B')
+
+If you were to read ARGB pixels as uint32's, the alpha would be in the high byte, and the blue in the lowest byte.  In memory, these are stored little endian, so 'B' is first, then 'G', 'R' and 'A' last.
+
+When calling conversion functions, the names match the FOURCC, so in this case it would be I420ToARGB().
+
+All formats can be converted to/from ARGB.
+
+Most 'planar_functions' work on ARGB (e.g. ARGBBlend).
+
+Some are channel order agnostic (e.g. ARGBScale).
+
+Some functions are symmetric (e.g. ARGBToBGRA is the same as BGRAToARGB, so its a macro).
+
+ARGBBlend expects preattenuated ARGB. The R,G,B are premultiplied by alpha.  Other functions don't care.