PREPRESS - WEB OFFSET PRINTING

Color Correction guide

Converting Color to CMYK

This is a quick method for converting an RGB or LAB image to CMYK while retaining much of the color fidelity of the original. This method also optimizes the CMYK image for use on Marrakech Express web offset presses.

Images should be scanned in LAB or RGB mode, as these are larger color spaces and will capture more information. The resultant images must be converted to CMYK before use. This document outlines our preferred method to converting images to CMYK. To correctly convert an image to CMYK, the CMYK setup in Photoshop needs to be set properly. Go to File/Color Settings/CMYK Setup in Photoshop 5 (Printing Ink Preferences in Photoshop 3 and 4) and set the CMYK preferences to the following:

Separation: GCR

Black Generation: Light

Black Ink Limit: 80%

Total Ink Limit: 240%-280% (depends on paper)

UCA amount: 0%

Then, open the Curves menu (command-M, or Image/Adjust/Curves…) and double-click on the left eyedropper (it looks filled with black ink). This will bring up the color picker dialogue. Set the CMYK values to 0% for Cyan, Magenta and Yellow, and 85% for Black. Leave all other values untouched. Click OK.

Double-click on the middle eyedropper and set 0% for Cyan, Magenta and Yellow, and 35% for Black. Click OK.

Double-click the right eyedropper (it looks empty) and set 0% for Cyan, Magenta and Yellow, and 2% for Black. Click OK.

Click on the “Auto” button. This will apply the values you have just set to the image. You can now convert the image to CMYK (using Image/Mode/CMYK Color). Return to the Curves menu to adjust the image contrast back to that of the original. Try to create a smooth “S” curve, preferable using the 25% and 75% nodes for adjustment. do not alter the endpoints of the line. Always check to make sure the image is not suffering due to the changes you are making.