Press match for color chips

[jotterpinky]

Question for all you experts in color management. I have a customer wanting to print out swatch sheets of all his paint colors for metal roofing. There are about 60 different colors, the previous printer did a horrible job matching the colors. I and my customer understand that we won't be able to match perfectly with 4-color process but would like to get a close approximation.

I started by using our i1 spectrophotometer and got a reading from each paint chip. The software allows me to export the swatches as an Illustrator swatch book but wants to know which color space to use, e.g. RGB, CMYK, Lab. Further it allows me to choose an ICC profile for each of these color spaces, e.g. GraCol, sRGB etc.

My question is what settings would give the best color match to begin design in, then eventually output to the press? We currently use the Gracol coated profile in our design software and design in CMYK. Final output will be on a 4-color press.

Or perhaps there is a different approach to doing this that I'm not aware of. If anyone is doing contract work like this that has prior experience it would be much appreciated, or perhaps some helpful tips for ways they've matched color before doing similar work.

 

[gordo]

You could use BabelColor's PatchTool to compare the Lab values to the GRACoL ICC Profile you're using to get delta E values. You could also use Chromix color think to do the same. You need to establish what dE method you'll use and establish how far out you can be and still have a match that your customer will accept.

You also need to clarify that you will be doing a colormetric match and not a sectoral match. I.e. the color in the brochure may shift dramatically under different lighting conditions compared with the ain't chips. This caveat should be stated in mouse print in the brochure itself. E.g. Colors in this brochure are approximate. Please see actual paint samples before choosing your color.

Best gordo

 

[rich apollo]

You could work in CMYK (keeping the swatch colors in L*a*b*), save as/export to PDF (without converting!!!!), and then convert only the L*a*b* colors in Acrobat.

 

[Slyoder]

We have done some of this in the past. While this might not be the easiest method, I've found that taking your CieLab readings from your spectro and creating Lab swatches in InDesign works well for me. You can then choose an output profile appropriate for the conditions the job gets printed on. Our last job got printed offset. We print using G7 to target GRACol2006_Coated1v2. Therefore I had Indesign convert the lab swatches to the Gracol profile when exporting to pdf.

You will probably find that not all the colors will match on the first attempt. Especially Clay, Almond, Grays etc. I am fortunate to have a proofer that gives me a very close representation of what my press will print. I will print out a proof and then compare it to the color chips. I then take my spectro and read the proof and compare the readings to original readings of the paint chips. It really helps to understand CieLab at this point. I'll be honest, I usually have a CieLab diagram handy for reference. I will then modify the Indesign swatches accordingly. For instance let's say the paint chip has an a* of 13.05 the proof reads 17.68. The proof is probably magenta casted at that point. I will then modify the Indesign swatch a* value from 13.05 to 8.42. (17.68 -13.05= 4.63 the difference) (13.05-4.63=8.42 suggested correction).

I will usually enter all my readings in a spread sheet and write a formula to calculate the differences and suggested corrections. I don't know if this is an approved method of doing this but it seems to work pretty well for me.

Good Luck, Steve

 

[Slyoder]

You said you design in CMYK. If you allow InDesign to convert to profile on export and the embedded profiles in the images are different from the output profile it will change the CMYK values of the images. If you setup the color settings in InDesgin to match your output, you mentioned Gracol, when you open the InDesign file you will get a CMYK color warning if any of the images have a different profile embedded. If you then click on "Adjust document to match current color settings" and under "placed content" Select "Disable all profiles" the CMYK images will now remain unchanged on output. I believe you have to do this every time you open the file.