[whatwg] Canvas operators (was Re: several messages)

Philip Taylor excors+whatwg at gmail.com
Sun May 20 18:22:03 PDT 2007

On 20/05/07, L. David Baron <dbaron at dbaron.org> wrote:
> I thought what Safari does is basically "lighter", but with the
> color components inverted (where inverting is CX = 1-CX, or cX = aX
> - cX), so that it comes out to:
>  aO = min(1, aA + aB)
>  cO = aO - min(1, aA - cA + aB - cB)

Aha, that does indeed match what Safari does exactly - I thought I'd
tried that before, but must have done something wrong.

> Hrm.  I thought lighter was confusingly *like* darker, in that they
> act exactly the same when the alphas add to less than or equal to 1.
> (I think that's true for plus (a.k.a. lighter), Cocoa's darker, and
> for saturate.)

I thought it may be more common to have alpha=1 on source and
destination - then you get
  red lighter green = yellow
  red saturate green = green
  red darker green = black
so they don't seem that much alike, except when looking in the range
where they do seem alike. But I have no idea how people tend to really
use these things in practice, and whether they give similar results in
those cases...

> -David

Philip Taylor
excors at gmail.com

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