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Old 2nd September 2002, 14:44   #1  |  Link
bergi
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best rgb yuv conversation

I'm testing some wavelet transform, using rgb and yuv color format. I've found many different conversation formulars with different loss, and different ranges, but what formular is used in the standart windows codecs?
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Old 6th September 2002, 12:45   #2  |  Link
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When I need that conversion, I used the formula that caused an YUV overlay to look exactly as the RGB-original.

The AVI file format descriptions I have say

Y = 0.299 R + 0.587 G + 0.114 B
U = 0.493 (B - Y)
V = 0.877 (R - Y)

But for my overlay, it definitely didn't work. The colors were somehow "weak". I had to scale the values.

I really don't remember the formula any more, since I did that a year ago or even more, but you can try to extract it from my RGB->YUV source code:

http://www.alexander-noe.de/Video/RGBNYUV/

Last edited by alexnoe; 6th September 2002 at 13:35.
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Old 8th September 2002, 01:41   #3  |  Link
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Your formulas are wrong.
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Old 8th September 2002, 14:20   #4  |  Link
alexnoe
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They are not "my" formulas...they are copy+pasted from an AVI file description.

I know that they can't be correct. As I said, the color was somehow weak if I used them for a RGB->YUV conversion and copied it to an overlay.

Would you be so kind to give the correct ones? You seem to know them...would you mind to share your knowledge?
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Old 8th September 2002, 17:30   #5  |  Link
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By converting avisynth code to formula I get this (rec601):

scaled_Y = 0.299 R + 0.587 B + 0.114 G
Y = 0.859 scaled_Y + 16
U = 0.496 (B - scaled_Y) + 128 (needs clipping)
V = 0.627 (R - scaled_Y) + 128 (needs clipping)

or if you prefer:

Y = 0.257 R + 0.504 G + 0.098 B + 16
U = -0.148 R - 0.291 G + 0.439 B + 128
V = 0.439 R - 0.368 G - 0.071 B + 128

That's assuming the standard representation of 8 bits/components, of course.
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Old 9th September 2002, 05:09   #6  |  Link
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That looks much better.
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Old 9th September 2002, 09:06   #7  |  Link
bergi
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Thanks!

An other question, there are many different types yuv color formats like yuv12.

i think standard is yuv12 and looks like this

---------
|yuv|y |
---------
|y |y |
---------


Can anybody tell me a good page about yuv color formats or explain it on the forum?
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Old 9th September 2002, 09:12   #8  |  Link
alexnoe
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yv12 is (at least for DirectDraw overlays)


------------------
|yyyyyyy...
|yyyyyyy...
|yyyyyyy...
|yyyyyyy...
|v v v v...
|
|v v v v...
|
|u u u u...
|
|u u u u...
|


Unfortunately, the page were I found this some time ago is down

EDIT
does anyone have an idea why there are different RGB->YUV formulas? I can promise that the last one won't work with DirectDraw overlays...

Last edited by alexnoe; 9th September 2002 at 10:25.
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Old 9th September 2002, 13:42   #9  |  Link
mpucoder
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Different standards, and mistakes. Some people confuse YIQ, YCbCr, and YPbPr for YUV.

Edit: btw, DVD uses three different standards (ITU-601, aka SMPTE-170 M, is one), so if you are working with DVD source make sure you check which one was used to encode.
http://mpucoder.kewlhair.com/DVD/dvdmpeg.html

Last edited by mpucoder; 9th September 2002 at 13:50.
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