RepoMirrors/mpv
1
0
Fork 0
mirror of https://github.com/mpv-player/mpv synced 2025-01-31 12:11:52 +00:00
Code Issues Releases Wiki Activity

soem explanation

Browse Source 
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@5313 b3059339-0415-0410-9bf9-f77b7e298cf2
This commit is contained in:
arpi 2002-03-24 18:42:05 +00:00
parent 4a1e0aef9b
commit 7e32366a13
1 changed files with 51 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
DOCS/tech/colorspaces.txt Normal file
View File

@ -0,0 +1,51 @@
Huh. The planar YUV modes.
==========================
The most missunderstood thingie...
Let's see: (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 (surname unknown) suggests that there are problems with the above
formulae 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!
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 = Cv = red component (0=green 128=grey 255=red)
MPlayer side:
=============
In MPlayer, we usually have 3 pointers to the Y, U and V planes, so it
doesn't matter what is they order in memory.
But there are some codecs (vfw, dshow) and vo drivers (xv) ignoring the 2nd
and 3rd pointer, and 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