CKMY craziness...

[Boudewijn Rempt]

On Mon, 22 Nov 2004, Saem Ghani wrote:

> On Monday 22 November 2004 10:47, Boudewijn Rempt wrote:
> > On Mon, 22 Nov 2004, Cyrille Berger wrote:
> > > how fast (or slow) is it to change from a color space to an other one ?
> >
> > Not that bad, it depends a bit on the colour space -- cmyk is a fair bit
> > slower than gray or rgb. It's basically another filter that needs to
> > handle every pixel, so much is dependent on the effciency of iterators
> > or other ways of accessing pixels.
>
> If I understand it correctly, it's actually quite costly.  You iterate over
> the entire image and unless it fits in cache -- unlikely -- it's going to run
> very slowly since you're going to be bound by the system bus, even though
> it'll be streamed over and be efficient as memory accesses go, there are
> really no cache wins so it's something worth avoiding/optmizing.
>

That holds for the entire rendering process -- currently it's really simple-minded,
but no matter what, we'll arrive at a situation where even RGB layers will have
a pixel-by-pixel conversion for display on a calibrated screen. So it would pay
to make that process as fast as possible, fast enough no matter what the complexity.