[cairo] Subtractive API, part 0

[Arjen Nienhuis]

>> That means that if i try to draw a cmyk(0, 0, 1, 1) box that is not pixel aligned I will get beige borders.
>
> It will not. For drawing it will use the fallback which is going, even
> with that super-simple conversion algorithm above, to be perfect gray,
> because cmyk (0, 0, 0, 0) is most probably rgb(0, 0, 0) and half of
> such black is rgb(127, 127, 127).
>
> In other words, if it was done your way, i.e. CMYK -> some other color
> space -> there cut it to half -> covert back to CMYK, you will never
> get cmyk(0, 0, 0.5, 0.5) out of half cmyk(0, 0, 0.5, 0.5). You will
> get something like cmyk(0.00123, 0.0173, 0.5763, 0.63454). But what if
> you printer does not have cyan and magenta?
>

Does anyone know what Photoshop does in that case: what happens if you
draw with a cmyk(0,0,1,1) brush with 50% opacity? Or with the borders?

The point of my message was that It's bad to do composition in CMYK
without a full blown CMS. If we don't want a CMS, we can use the SVG
model with sRGB fallbacks.