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diff --git a/DOCS/OUTDATED-tech/colorspaces.txt b/DOCS/OUTDATED-tech/colorspaces.txt deleted file mode 100644 index eaf9d221e4..0000000000 --- a/DOCS/OUTDATED-tech/colorspaces.txt +++ /dev/null @@ -1,158 +0,0 @@ -In general -========== - -There are planar and packed modes. -- Planar mode means: You have 3 separate images, one for each component, -each image 8 bits/pixel. To get the real colored pixel, you have to -mix the components from all planes. The resolution of planes may differ! -- Packed mode means: you have all components mixed/interleaved together, -so you have small "packs" of components in a single, big image. - -There are RGB and YUV colorspaces. -- RGB: Red, Green and Blue components. Used by analog VGA monitors. -- YUV: Luminance (Y) and Chrominance (U,V) components. Used by some - video systems, like PAL. Also most M(J)PEG/DCT based codecs use this. - -With YUV, they used to reduce the resolution of U,V planes: -The most common YUV formats: -FOURCC: bpp: IEEE: plane sizes: (w=width h=height of original image) -444P 24 YUV 4:4:4 Y: w * h U,V: w * h -YUY2,UYVY 16 YUV 4:2:2 Y: w * h U,V: (w/2) * h [MJPEG] -YV12,I420 12 YUV 4:2:0 Y: w * h U,V: (w/2) * (h/2) [MPEG, H.263] -411P 12 YUV 4:1:1 Y: w * h U,V: (w/4) * h [DV-NTSC, CYUV] -YVU9,IF09 9 YUV 4:1:0 Y: w * h U,V: (w/4) * (h/4) [Sorenson, Indeo] - -The YUV a:b:c naming style means: for <a> samples of Y there are <b> samples -of UV in odd lines and <c> samples of UV in even lines. - -conversion: (some cut'n'paste from www and maillist) - -RGB to YUV Conversion: - Y = (0.257 * R) + (0.504 * G) + (0.098 * B) + 16 - Cr = V = (0.439 * R) - (0.368 * G) - (0.071 * B) + 128 - Cb = U = -(0.148 * R) - (0.291 * G) + (0.439 * B) + 128 -YUV to RGB Conversion: - B = 1.164(Y - 16) + 2.018(U - 128) - G = 1.164(Y - 16) - 0.813(V - 128) - 0.391(U - 128) - R = 1.164(Y - 16) + 1.596(V - 128) - -In both these cases, you have to clamp the output values to keep them in -the [0-255] range. Rumour has it that the valid range is actually a subset -of [0-255] (I've seen an RGB range of [16-235] mentioned) but clamping the -values into [0-255] seems to produce acceptable results to me. - -Julien (sorry, I can't recall his surname) suggests that there are -problems with the above formula and proposes the following instead: - Y = 0.299R + 0.587G + 0.114B - Cb = U'= (B-Y)*0.565 - Cr = V'= (R-Y)*0.713 -with reciprocal versions: - R = Y + 1.403V' - G = Y - 0.344U' - 0.714V' - B = Y + 1.770U' -Note: This formula doesn't contain the +128 offsets of U,V values! - -Conclusion: -Y = luminance, the weighted average of R G B components. (0=black 255=white) -U = Cb = blue component (0=green 128=grey 255=blue) -V = Cr = red component (0=green 128=grey 255=red) - - -Huh. The planar YUV modes. -========================== - -The most misunderstood thingie... - -In MPlayer, we usually have 3 pointers to the Y, U and V planes, so it -doesn't matter what the order of the planes in the memory is: - for mp_image_t and libvo's draw_slice(): - planes[0] = Y = luminance - planes[1] = U = Cb = blue - planes[2] = V = Cr = red - Note: planes[1] is ALWAYS U, and planes[2] is V, the FOURCC - (YV12 vs. I420) doesn't matter here! So, every codec using 3 pointers - (not only the first one) normally supports YV12 and I420 (=IYUV), too! - -But there are some codecs (VfW, dshow) and vo drivers (xv) ignoring the 2nd -and 3rd pointer that use only a single pointer to the planar YUV image. In -this case we must know the right order and alignment of planes in the memory! - -from the webartz fourcc list: -YV12: 12 bpp, full sized Y plane followed by 2x2 subsampled V and U planes -I420: 12 bpp, full sized Y plane followed by 2x2 subsampled U and V planes -IYUV: the same as I420 -YVU9: 9 bpp, full sized Y plane followed by 4x4 subsampled V and U planes - -Huh 2. RGB vs. BGR ? -==================== - -The 2nd most misunderstood thingie... - -You know, there are Intel and Motorola, and they use different byteorder. -There are also others, like MIPS or Alpha, but all follow either Intel -or Motorola byteorder. -Unfortunately, the packed colorspaces depend on CPU byteorder. So, RGB -on Intel and Motorola means different order of bytes. - -In MPlayer, we have constants IMGFMT_RGBxx and IMGFMT_BGRxx. -Unfortunately, some codecs and vo drivers follow Intel, some follow Motorola -byteorder, so they are incompatible. We had to find a stable base, so long -time ago I've chosen OpenGL, as it's a wide-spreaded standard, and it well -defines what RGB is and what BGR is. So, MPlayer's RGB is compatible with -OpenGL's GL_RGB on all platforms, and the same goes for BGR - GL_BGR. -Unfortunately, most of the x86 codecs call our BGR RGB, so it sometimes -confuses developers. - -memory order: name -lowest address .. highest address -RGBA IMGFMT_RGBA -ARGB IMGFMT_ARGB -BGRA IMGFMT_BGRA -ABGR IMGFMT_ABGR -RGB IMGFMT_RGB24 -BGR IMGFMT_BGR24 - -order in an int name -most significant .. least significant bit -8A8R8G8B IMGFMT_BGR32 -8A8B8G8R IMGFMT_RGB32 -5R6G5B IMGFMT_BGR16 -5B6G5R IMGFMT_RGB16 -1A5R5G5B IMGFMT_BGR15 -1A5B5G5R IMGFMT_RGB15 - -The following are palettized formats, the palette is in the second plane. -When they come out of the swscaler (this can be different when they -come from a codec!), their palette is organized in such a way -that you actually get: - -3R3G2B IMGFMT_BGR8 -2B3G3R IMGFMT_RGB8 -1R2G1B IMGFMT_BGR4_CHAR -1B2G1R IMGFMT_RGB4_CHAR -1R2G1B1R2G1B IMGFMT_BGR4 -1B2G1R1B2G1R IMGFMT_RGB4 - -Depending upon the CPU being little- or big-endian, different 'in memory' and -'in register' formats will be equal (LE -> BGRA == BGR32 / BE -> ARGB == BGR32) - -Practical coding guide: - -The 4, 8, 15, and 16 bit formats are defined so that the portable way to -access them is to load the pixel into an integer and use bitmasks. - -The 24 bit formats are defined so that the portable way to access them is -to address the 3 components as separate bytes, as in ((uint8_t *)pixel)[0], -((uint8_t *)pixel)[1], ((uint8_t *)pixel)[2]. - -When a 32-bit format is identified by the four characters A, R, G, and B in -some order, the portable way to access it is by addressing the 4 components -as separate bytes. - -When a 32-bit format is identified by the 3 characters R, G, and B in some -order followed by the number 32, the portable way to access it is to load -the pixel into an integer and use bitmasks. - -When the above portable access methods are not used, you will need to write -2 versions of your code, and use #if HAVE_BIGENDIAN to choose the correct -one. |