Computer Graphics with Photoshop - Convert CMYK curves to RGB curves???

Author

Convert CMYK curves to RGB curves???

arkarda

2006-03-20, 6:16 pm

alright got a problemo! there are a few progs out there that read
photoshop curves files and duplicate the result in their own curves
facility.
KOOL!

But I was doing something vey intereasting with the CMYK colorspace
and saved the result as a curve AMP file.

Loaded the AMP file into the program , and.....got a completely
different result!
Very soon I realized it only accepted RGB colorspace as alot of image
editors
and vdeo tools do.Is there a wave to CONVERT in photoshop or other
software
a CMYK curve into an RGB curve (or as close in RGB colorspace) and
save out as an AMP file.

Anybody providing the answer would save my bacon.BIG TIME.

thanks in advance,

arkarda.

Mike Russell

2006-03-20, 6:18 pm

"arkarda" <arkarda@hotmail.com> wrote in message
news:1142876578.915836.37220@t31g2000cwb.googlegroups.com...
>
> alright got a problemo! there are a few progs out there that read
> photoshop curves files and duplicate the result in their own curves
> facility. KOOL!
>
> But I was doing something vey intereasting with the CMYK colorspace
> and saved the result as a curve AMP file.
>
> Loaded the AMP file into the program , and.....got a completely
> different result!
> Very soon I realized it only accepted RGB colorspace as alot of image
> editors
> and vdeo tools do.Is there a wave to CONVERT in photoshop or other
> software
> a CMYK curve into an RGB curve (or as close in RGB colorspace) and
> save out as an AMP file.
>
> Anybody providing the answer would save my bacon.BIG TIME.

Have you tried to manually get a set of RGB curves that give a result
similar to your CMYK result? If you cannot do this reasonably well, the
odds are slim that a good conversion is possible.

It is certainly possible to convert your CMYK curve to an approximate RGB
curve if it stays within certain limits. The accuracy of the final curve
may be limited because CMYK includes a fourth K channel that is not present
in RGB mode. If you are performing heavy manipulations on the K channel,
the accuracy will be poor because there is no K channel in RGB. Modifying
the shadow in RGB generally requires changing all three channels.

FYI. There is another procedure called "curve extraction" that involves
curving the image in CMYK, converting to RGB and extracting the curve using
Curvemeister's pinning feature. Photoshop would then be used to convert the
curve to AMP format. This may be also be done manually using Photoshop
curves with a little extra book keeping.

The following tutorial shows how to use curve extraction to approximate a
camera white balance setting. The same technique may be adapted to your
CMYK curve.
http://www.curvemeister.com/tutoria...tion/index.html
--
Mike Russell
www.curvemeister.com