[PD-dev] Re: [PD-announce] pdp v0.7

[tigital]

>  > btw, i have a color conversion problem
>>  and as people spoke about YUV/RGB colormaps,
>>  i may ask for an advice here :
>>
>>  i'm using color conversions from effectv, the formulas are :
>>
>>  /*
>>   * conversion from YUV to RGB
>>   *   r = 1.164*(y-16) + 1.596*(v-128);
>>   *   g = 1.164*(y-16) - 0.813*(v-128) - 0.391*(u-128);
>>   *   b = 1.164*(y-16)                 + 2.018*(u-128);
>>   * conversion from RGB to YUV
>>   *   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
>>   */
>>
>
>i use exactly the same formula for conversion from the rgb colour model from
>v4l and i've noticed some differences too compared to directly capturing in
>yuv.. maybe the standard is not that standard?
>
>this page mentions another formula, along side the one above. maybe you can
>try that one?
>
>http://www.fourcc.org/fccyvrgb.htm
>
weird...

...I use the following conversions for gamma-corrected RGB and YUV:

Y = 0.299R + 0.587G + 0.114B
U = -0.147R - 0.289G + 0.436B
   = 0.492 ( B - Y )
V = 0.615R - 0.515G - 0.100B
   = 0.877 ( R - Y )

R = Y + 1.140V
G = Y - 0.395U - 0.581V
B = Y + 2.032U

...of course, it turns out that it all depends on what the original 
RGB is in, and differs if it's 16-235 or 0-255 per channel, and 
whether your going for YUV, YCbCr:HDTV (Y709) or YCbCr:SDTV 
(Y601)...for the record, the effectv conversions are Y601 based, with 
RGB channels of 0-255...

another good reference is:
http://www.faqs.org/faqs/graphics/colorspace-faq/

l8r,
jamie
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