Two colour contract proof

[SilvaJr]

We have a little request that will help our sheetfed printers.

We are working under ISO 12647 matching our runs against the proofs exported from Prinergy (pdfs or tiffs). Contract proofs are created in EFI Colorproof XF, printed in an Epson 9900.

We have a two colour press, and occasionally we use that press to run four color work. This means that they have to print cyan and magenta first, and then on the next pass yellow and black.

In order to help them with colour management on the first pass, is it possible to output a proof that has just the magenta and cyan separations?

We have looked at other areas like Pitstop, Acrobat, Prinergy Process templates, but I will appreciate any comments on that.

Thanks

[kyle]

If the software generating the proofs uses a regular CMYK ICC format file (usually with a ".icc" or ".icm" extension) for the press/output profile, you can probably create an alternate profile to use for your "first pass" proofs.

The CMYK to L*a*b*/XYZ part of the profile that is used for the conversion has three sections that are used sequentially: first the input CMYK channels are independently modified with discrete input "curves" (that are usually linear and don't modify the values); then the resulting CMYK values are found in a four-dimensional look-up table to find the appropriate L*a*b*/XYZ values using interpolation; finally the resulting L*a*b*/XYZ values are modified with discrete output curves. That yields the device-independent color value for the CMYK mix.

If you suppress the yellow and black to zero in the input curves, the cyan and magenta will be isolated. E.g., 70/34/33/20 CMYK would output the same as 70/34/0/0 CMYK. If you don't have software that can accomplish this, I can modify the file for you if you upload it (make sure it's the press/output profile, not the proofer profile).

This of course hinges on your ability to match the four-color proof after the second pass. Are you often able to match your four-color proofs with your two-color press? If so, then this should work using the same profile with the yellow and black suppressed. I don't have much experience with the CMYK on a two-color press scenario, but I would guess that you would have to use a profile based on measurements of CMYK printed two colors at a time to get really close, considering you're dry trapping on the second pass. I'd be interested in any input anyone has (Gordo?) about the differences, similarities and challenges of two-pass CMYK versus one pass.

[Stephen Marsh]

J, in Prinergy, create a loose page output to vector PDF. Use the colour mapping to exclude the YK plates. This is one way to create input data for a "progressive proof". I have attached a screenshot for your reference. You would provide two proofs, a CM only proof and a CMYK proof. If the press operators are printing for ISO conditions, they should be aiming for specific density values anyway, so I am not sure how useful the progressive proof will be as that is encouraging them to eyeball output rather than printing "to the numbers".

As you are using two different RIP's, one for plating (Prinergy) and one for "proofing" (EFI) - I am not sure if this is an optimal workflow. Do you ever have discrepencies between the two RIPs? You could proof a CM PDF from Prinergy, as well as the CMYK PDF from Prinergy, then at least the PDF has been refined by the RIP that will be plating - however this only goes so far as both RIPs are still different.

Another option if the EFI proofing RIP has it, would be to send your Prinergy RIPed and separated 1-bit TIFFs for the C & M plates, where the proofing RIP would combine and colour manage the separations back to composite. There would likely be an option to downsample and descreen the plate files, or to simply downsample them to proofer resolution while retaining the plate screening.

Yet another option could be to create a Prinergy loose page output to raster format at say 720ppi for the progressive CM and or CMYK proofs, then at least Prinergy is rasterizing the file and the same RIP is being used for rasterizing the proof and the plate data.

I also agree with the last paragraph from Kyle's post, I think this needs looking into a bit deeper.


Hope this helps,

Stephen Marsh

[SilvaJr]

Thank you for your input. We did it progressive proofs by colour mapping the YK channels excluding the colors. I'm looking forward the see the samples on press.

Thanks,

[Stephen Marsh]

Thank you for your input. We did it progressive proofs by colour mapping the YK channels excluding the colors. I'm looking forward the see the samples on press.

Thanks,

Please post back with your feedback, I am interested to find out how things go!


Stephen Marsh