Binary FX: Photoshop Tech Vault 3.0

Binary FX: Photoshop Tech Vault 3.0 | < | >

Combine Separations in Photoshop

How To:

Proof the separated PostScript output of your illustration or page layout software in Photoshop, before going to press.

If your work is printed in more than one colour on a press, it is often wise to proof the final page layouts for common issues related to producing separations in a PostScript workflow, such as overprinting and even more so when transparency effects and spot colours are in use. Many Adobe graphics applications now provide press related soft-proofing options, but it can often be wise to take the time for a pre-proof before sending a critical job out for printing.

One can simply directly print separations to a PostScript laser printer or produce soft-proof PDF files of the separations for visual evaluation to the original composite, or Photoshop can be used to combine separations to mimic the final composite print created from the separations. This 'extra' proofing is often needed for critical jobs where one does not have the ability to see the final separations until things are too late (some RIP's have the ability to combine separations to provide more accurate proofing than composite printing provides).

Printing Separations To PostScript File:

If you only have page layout software and Photoshop, produce a single page PostScript file for each separation of each page in the print run. If you have Acrobat Distiller then you can make a single, multi-page, pre-separated PostScript file.

Validating and Rasterizing the PostScript file:

Acrobat Distiller is often useful as it can indicate common PostScript errors that may not be apparent earlier in the workflow which would also become apparent later in the workflow at the service providers RIP when imaging film or plates. One can create PDF files from PostScript data to validate the data and also to pre-process the data for Photoshop. Acrobat Distiller will accept a multi-page .ps file and create a multi-page PDF file.

For proofing speed, resolutions of 200-300 ppi may often be used, while higher resolutions provide more accurate rendering of trapping, lineart, text and vector data. Once each separate .ps file has been rasterized into Photoshop as grayscale mode data, or the Automate command has been used to create .psd files from the multi-page .pdf file - one can then combine the separations into the final composite proof.

Combining Rasterized Separations:

Flatten the grayscale files and use the Merge Channels command found in the channels palette options menu to combine the separations. Ensure that CMYK mode is chosen and that the correct colour plate is chosen for each of the four channels. If necessary, one can create alpha channels and manually apply any extra spot channel data to these channels and set them as a spot channel with the appropriate spot colour library data.

Although this procedure can take time, due to the differences between PostScript printing of composite and separated data, it can be wise to take nothing for granted when it comes to the later stages of print production. Now that computer to plate is common, unlike film, one may never see the separations that will be used on press.

Related External Link:

CreativePro: White Overprint Gotchas

< | > | ^ | How To Home | Home