Rendering Intent

[Kid_Leo]

I am setting up color proofing using a Xitron GPS RIP driving an Epson 9800. Originally the system was setup using the stock "Proofready" settings and I was pretty happy with the color reproduction until I came across one job. This job contained a maroon backround color that had a slightly darker maroon color pattern over the top giving the appearance somewhat like wallpaper. This proof did not look as it should the lighter and darker colors simply blended together and basically the pattern did not show up even though it printed fine on press. In the end the basic color of the proof was pretty accurate to the press sheet except for the pattern being lost on the proof.

The short story is that I did a lot of experimenting and created my own color settings that utilize a Gracol profile that I downloaded as my input and a the appropriate Epson profile for output. I found that the rendering intent was the setting that was causing the background/foreground to blend together. If I use colormetric as the intent they blended together, if I use perceptual they come out OK.

I found a very good article explaining how intents work and feel I have a good understanding of them. The article said that intents deal with colors that are outside the gamut you are using and how to reproduce them. My conclusion was that the darker maroon color was outside the gamut and when I used the colormetric setting it was changed to be inside the GRACOL gamut and was changed to the same color as the lighter maroon color hence the contrast disappeard. Conversly by using a relative setting the lighter maroon was made to be an even lighter shade so that the darker maroon could take its place and still show contrast.

What I don't understand is why the intent should be changing anything. The colors in my input file are all defined as CMYK so nothing should be falling outside of the gamut of either the GRACOL gamut or of the Epson.

Can someone shed some light on this for me or am I barking up the wrong tree?

FYI the colors in question are defined as follows:
Lighter color C=3, M=93, Y=70, K=40
Darker color C=3, M=98, Y=70, K=45

[ColorTyrant]

Originally Posted by Kid_Leo

What I don't understand is why the intent should be changing anything. The colors in my input file are all defined as CMYK so nothing should be falling outside of the gamut of either the GRACOL gamut or of the Epson.
5

Kid_Leo, it's quite possible that there are a few colors within the Gracol gamut that your Epson's profile gamut just can't hit. When I compare the gamut of GRAGoL's GRACoL2006_Coated1v2.icc profile to a profile created from our Epson 4800, I find that even though the Epson's gamut is larger on the whole, there are some colors near the A axis (shades of magenta) that Gracol can hit, but the Epson can't. We also use the GRACoL2006_Coated1v2.icc profile as an input profile when proofing to our Digital CMYK Halftone Proofer and have found that there are colors that the proofer is able to hit on it's own that aren't achievable when the GRACoL profile is loaded.

[Kid_Leo]

ColorTyrant, wow!, that's very interesting. I never dreamed that in our little CMYK world that the Epson couldn't do it all with with 8 inks. It must be just my dumb luck that on the 5th or 6th job that I proofed on this setup it didn't come out correctly. I was really wondering if I had bought a lemon, although I haven't actually paid for it yet.

How can I verify that the Epson's gamut is the problem? You mentioned "comparing" profile gamuts, is this something that I could do?, what does it require? The reason I am so hung up on this is that when I took on buying this equipment I promised the "powers that be" that I would get good proofs and I want to make sure that is true before I sign off on the equipment. If the limitation is the Epson I can live with that, especially if the problem is few and far between. If the problem is the RIP software, I may look for a better solution.

As a more general question, what intent should I be using on a day-to-day basis for proofing CMYK work?

[ICC_Color_Management]

Hi Kid_Leo,

to compare the gamut of Gracol and your Epson you can download a free 3D Gamut Viewer at TGLC - PerfX 3D Gamut viewer™ - 3D color gamut visualization

ICC_Color_Management

Originally Posted by Kid_Leo

ColorTyrant, wow!, that's very interesting. I never dreamed that in our little CMYK world that the Epson couldn't do it all with with 8 inks. It must be just my dumb luck that on the 5th or 6th job that I proofed on this setup it didn't come out correctly. I was really wondering if I had bought a lemon, although I haven't actually paid for it yet.

How can I verify that the Epson's gamut is the problem? You mentioned "comparing" profile gamuts, is this something that I could do?, what does it require? The reason I am so hung up on this is that when I took on buying this equipment I promised the "powers that be" that I would get good proofs and I want to make sure that is true before I sign off on the equipment. If the limitation is the Epson I can live with that, especially if the problem is few and far between. If the problem is the RIP software, I may look for a better solution.

As a more general question, what intent should I be using on a day-to-day basis for proofing CMYK work?

[Kid_Leo]

ICC, thanks for the link. I downloaded it and can load my input profiles into it and compare them. Unfortunately, it appears that I don't have the output profiles as true ICC profiles. The Harlequin requires that profiles to be "imported" which looks like it changes them into Postscript language for the RIP. The output profiles I am using came with the RIP and do not appear to be on the system as plain ICC profiles.