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some typos

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git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@5736 b3059339-0415-0410-9bf9-f77b7e298cf2
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alex 2002-04-20 21:01:41 +00:00
parent 2520714269
commit 5d1588bb81
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29
DOCS/tech/colorspaces.txt
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@ -3,7 +3,7 @@ In general
There are planar and packed modes.
- Planar mode means: you have 3 separated image, one for each component,
each image 8 bites/pixel. To get the real colored pixel, you have to
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.
@ -37,16 +37,16 @@ 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 (surname unknown) suggests that there are problems with the above
formulae and suggests the following instead:
Y = 0.299R + 0.587G + 0.114B
Julien (sorry, I can't call back his surname) suggests that there are
problems with the above formula and suggests 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 formule doesn't contain the +128 offsets of U,V values!
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)
@ -57,7 +57,7 @@ V = Cr = red component (0=green 128=grey 255=red)
Huh. The planar YUV modes.
==========================
The most missunderstood thingie...
The most misunderstood thingie...
In MPlayer, we usually have 3 pointers to the Y, U and V planes, so it
doesn't matter what is the order of the planes in the memory:
@ -82,23 +82,22 @@ YVU9: 9 bpp, full sized Y plane followed by 4x4 subsampled V and U planes
Huh 2. RGB vs. BGR ?
====================
The 2nd most missunderstood thingie...
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, they all follow either Intel
or Motorola byteorder.
Unfortunatelly, the packed colorspaces depend on CPU byteorder. So, RGB
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.
Unfortunatelly, some codecs and vo drivers follow Intel, some follow Motorola
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 choose OpenGL, as it's a wide-spreaded standard, and it well
defines what is RGB and what is BGR. So, MPlayer's RGB is compatible with
OpenGL's GL_RGB on all platforms, and the same stay for BGR - GL_BGR.
Unfortunatelly, most of the x86 codecs call our BGR to RGB, so it sometimes
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 to RGB, so it sometimes
confuse developers.
If you are unsure, try the OpenGL driver (-vo gl). There is at least software
OpenGL implementation for all major platforms and OSes.
OpenGL implementation for all major platforms and OS's.