Re: [Lcms-user] Fast colour managed preview, how?

[Gerhard F. <nos...@gm...>]

Auke Nauta schrieb:

>Hi,
>
>For some time now I have been wondering how some applications, notably
>Photoshop, manage to show a colour managed image almost instantaneously.
>
>If I have to do it using lcms, I need to convert each pixel from input to
>monitor profile which is (relatively) slow.
>
Auke,

normally you won't convert each pixel with a separate call to the API 
function, but you will convert larger chunks, e.g. one scan line or even 
the whole image with a single call to cmsDoTransform().

I can confirm that the speed of LCMS has noticeably improved in one of 
the last few versions (I don't remember in which one), but I don't know 
your performance requirements.

If you need even faster transforms, I can recommend Argyll's IMDI 
routines (http://www.argyllcms.com - Do you remember? Marti has 
forwarded Graeme's announcement with the new URL today). Particularly if 
you can live with 8bpp input, then IMDI is _very fast_ (I measured circa 
14 Mpixels/second for a 3D -> 3D transform with 8bpp source and 8 or 
16bpp destination, on an AMD Athlon XP 2600+ with 2080MHz. This 
corresponds to circa 18 frames/second @ 1024x768).

And I suspect, that a non-portable implementation based on Intel's/AMD's 
MMX/3DNow/SSE2 instruction sets could be likely even faster.

I think PS also uses a trick to excite the impression of an instant 
update: It updates the screen nearly instantly at low resolution, and 
then continues in the background to refine the screen display up to full 
resolution (please correct me, if I'm wrong).

Regards,
Gerhard

>I suspect PS is directly addressing some kind of 3D LUT on the video card.
>I have (extensively) tried to find such kind of info (how to program the
>3D LUT) on the net, but to no avail :(
>
>Can anyone shed some light on this?
>
>TIA,
>Auke Nauta
>