On Sunday 24 September 2006 10:46, Rob Ogle wrote:

I'm trying to get a wedding chapel to move away from Photoshop and start using the Gimp. They are almost on board except for a printing issue. If we print a photo from Photoshop to an Epson Stylus 2200 the photo looks great. But when we print from the Gimp, the colors are "wrong". I don't know enough graphics terms to describe it. The picture has a greenish and/or faded quality to it.

We're running Gimp for Windows on a new XP Pro box w/ a P4 cpu, 1GB RAM and a 200GB drive.

Any suggestions?

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Photoshop and the free programs TeX, Scribus, Inkscape, Krita etc. can work in the CMYK color model. Gimp only works in RGB. CMYK has a more limited range of colors than RGB. Printers, both desktop and four color commercial work in CMYK.

This is the major hangup with using Gimp as a Photoshop replacement. Apparently adding the additional color model would be a huge undertaking.

On 9/27/06, John R. Culleton wrote:

Photoshop and the free programs TeX, Scribus, Inkscape, Krita etc. can work in the CMYK color model. Gimp only works in RGB. CMYK has a more limited range of colors than RGB. Printers, both> -- desktop and four color commercial work in CMYK.

This is the major hangup with using Gimp as a Photoshop replacement. Apparently adding the additional color model would be a huge undertaking.

Color management support is improved in the latest development versions of GIMP, this is not the same as editing in CMYK mode, but it should be the thing more than 90% of the people asking for CMYK needs, even though they think it is not.

It is sufficient to do the conversion to CMYK when exporting from GIMP to file/the printer to achieve correct colors if you have a color correction profile for your display as well as your printer. This is a separate issue from being able to work with the image in CMYK mode. Manipulating a photograph in CMYK mode is in most cases mostly pointless since the source of the data is the RGB model and the human visual system operates in RGB as well. The separation needed for CMYK varies between printers whilst sRGB is a standard color space for image exchange.

/Øyvind K.

On Wednesday 27 September 2006 18:03, Øyvind Kolås wrote:

Color management support is improved in the latest development versions of GIMP, this is not the same as editing in CMYK mode, but it should be the thing more than 90% of the people asking for CMYK needs, even though they think it is not.

It is sufficient to do the conversion to CMYK when exporting from GIMP to file/the printer to achieve correct colors if you have a color correction profile for your display as well as your printer. This is a separate issue from being able to work with the image in CMYK mode. Manipulating a photograph in CMYK mode is in most cases mostly pointless since the source of the data is the RGB model and the human visual system operates in RGB as well. The separation needed for CMYK varies between printers whilst sRGB is a standard color space for image exchange.

/Øyvind K.

Welll perception is everything. It is necessary for Gimp not to be as good as but better than its competition to gain acceptance. As soon as the CMYK lack is mentioned people in my industry are turned off and won't consider the product further.

The product of professional print designers today is not separations or an sRGB file but a PDF or tiff file in CMYK model. Prepress, making of separations etc. is a separate process. If conversion is done at the end of the designer's workflow then there is no chance to put back the brightness that is lost.

But there is perhaps a way to do it. If a display function can be added to Gimp whereby a double conversion is done, from RGB to CMYK and back again, then the user could view the illo in Gimp with the gamut limited to what it will be in CMYK model, and adjust saturation etc. to bring the photo back up to requirements. Since there is already a function to separate into CMYK colors it could possibly be a recombination of those separations into a single image.

In the meantime people like the OP who want to use Gimp instead of Photoshop in their workflow will need to understand its limitations for photos destined for print jobs and develop workarounds. We need to be honest about this up front.

On Thursday 28 September 2006 08:31, Rob Ogle wrote:

John,

I'm the OP'er...since I'm a network tech and not a graphic designer I want to make sure I understand what I'm getting from these posts before I go back to the designer. When you wrote, "...will need to understand its limitations for photos destined for print jobs and develop workarounds"

Does that mean that there is no fix? Or is the fix to convert the visible image to cmyk in the Gimp so the designer can adjust colors, etc so the print should match the screen?

That is more or less what I am asking for. The problem is the limited gamut of CMYK. What looks great in RGB looks dull in CMYK.

For serious color work you need a monitor that can be adjusted for color temperature and software that will accept icc profiles and so on. Then you need to run tests, perhaps with a calibrated color target. Photoshop has a lot of this stuff built in. Scribus, which lacks the plugins etc. of Gimp, nevertheless will deal with the CMYK model and ICC profiles. Of course ImageMagick and GraphicsMagick can do conversions back and forth. At this point however it is mostly cut and try with Gimp. You have to do a lot of tests on your setup to get it right.

I bought a used sony pro monitor on EBay, model CPD G250 and I have adjusted the color temperature to my flourescent environment. But I haven't gone much further with it,

I've been using the Gimp in a limited capacity for the past 4 years and I love it. I like to promote it as much as possible.

As do I, but the color model thing is serious and I have to be honest about it.

Hi,

On Thu, 2006-09-28 at 08:07 -0400, John R. Culleton wrote:

But there is perhaps a way to do it. If a display function can be added to Gimp whereby a double conversion is done, from RGB to CMYK and back again, then the user could view the illo in Gimp with the gamut limited to what it will be in CMYK model, and adjust saturation etc. to bring the photo back up to requirements. Since there is already a function to separate into CMYK colors it could possibly be a recombination of those separations into a single image.

This option exists since GIMP 2.2 (or even 2.0, I don't remember). It's called a Soft Proof and there's a display filter for it. With 2.4 it will become even easier to use this functionality.

Sven