🚀 go-pugleaf

In article <1370@se.alcbel.be>, cgra@btma74.nohost.nodomain writes:
>
> In article <1992Dec14.092349.11705@prl.philips.nl>, martens@prl.philips.nl (martens p) writes:
> |>>
> |>>I presume one of the advantages of RGB for software is that it's
> |>>additive: if you have two images that you want to mix, and you have
> |>>the pixels as R,G,B color components, mixing becomes trivial (just
> |>>average the components).  Many shading algorithms also use this
> |>>additive property extensively.  I don't think this is as easy for YUV.
> |>
> |>
> |>As far as I know, you don't even need a math processor to convert YUV <-> RGB:
> |>
> |>Y = 0.3 R + 0.59 G + 0.11 B
> |>U = 0.49 (B - Y)
> |>V = 0.88 (R - Y)
> |>
> So YUV is also additive, like anything else which goes
>      [ a11  a12  a13 ]  [R]     [foo]
>      [ a21  a22  a23 ]  [G]  =  [bar]
>      [ a31  a32  a33 ]  [B]     [baz]
>                              - right?

If you put it that way, *everything* is additive. :-)

Perhaps what Peter should have said is that "addition of RGB components has
a well-defined meaning". That is, its visual effect can be understood in
terms of what happens when you shine different coloured lights on the same
background.

Addition of YUV values doesn't make so much sense. Addition of Y components
is OK, but those negative coefficients in the formulas for U and V can cause
some strange effects.

Lawrence D'Oliveiro                       fone: +64-7-856-2889
Computer Services Dept                     fax: +64-7-838-4066
University of Waikato            electric mail: ldo@waikato.ac.nz
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