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+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.