M&G Electronic Prepress - Working with Color

Electronic Prepress:
Working with Color

Specifying Colors
The first decision to be made is if the colors are to print as spot inks (such as Pantone 185) or as traps of the four process colors: Cyan, Magenta, Yellow and Black. Even if you are specifying your job as four-color process, you may want to use a fifth spot color for critical color matches that are important in your design. Specifically, the lighter pastel colors sometimes used in backgrounds will contain a rosette pattern when simulated by the trapped four-color process model. Using a fifth spot color which does not contain the rosette pattern may produce a more pleasing appearance. Some colors simply do not trap as exact color matches of the Pantone colors. However, they are formulated as closely as the four-color process model allows. Neon, fluorescent, and metallic colors require the addition of the actual spot color ink.

When setting up colors in your desktop programs, please make sure you have your spot colors and process color specified as such. It is also important that you check the percentages of each process color used in traps and keep them consistent from one application to the next. For example, if you have specified a Pantone match to PMS 185 in Photoshop, again in Illustrator for your logo and again in PageMaker for your type, each of these programs uses internal formulation tables to determine what percent of each process color will be used to create the match. These percentages may be quite different from program to program. Note the percentages used in one application and adjust the values in the other applications to maintain consistency. You should never use the default Red, Green, or Blue colors that appear in the color menus. These represent the RGB spectrum which is not suitable for printing, and does not accurately represent the CMYK model.

When using spot colors, make sure to assign each a screen angle that corresponds to one of the process colors. Most applications assign the same angle as black—45°—by default but will allow you to change them.

When working in Photoshop or scanning color art, please work in CMYK mode. We realize that RGB files are smaller, having one less channel, and tend to produce more vibrant colors, particularly reds and blues. However, our presses print utilizing the four-color process model and cannot exactly duplicate the RGB model. RGB is an entirely different color gamut and when viewed on your computer screen then translated to CMYK off the press, will often produce surprising shifts in color reproduction. That is why we suggest translating modes on your computer to minimize surprises when you receive your CMYK color proof. You should be able to make adjustments to your scans utilizing the curves section in Photoshop if any evident color shifts occur when converting to CMYK mode. RGB files, if not converted to CMYK, will only output the black film (grayscale) of the four-color output.

Trapping
Also known as chokes and spreads, trapping is necessary between two colors that touch to prevent white gaps which would occur with the slight stretching and shifting of paper as it goes through the press. A trap is created by making a slight overlap—approximately 1/4 of a point—of the lighter color over the darker, or of a percentage of each color.

Our operators are specially trained to create traps to digital files and will do this for you. If, however, you are using a file where trapping has already been created for another use, we need to know in advance so we can ensure that it is accurate for our process. If you choose to perform the trapping function, you will be responsible for the output or additional cost to repair any problems.

Helpful hint:
Large areas of blends, such as backgrounds, have a tendency to band—the obvious stripes in the transition from one color or value to the other. To avoid this, create the band in a paint program like Photoshop and add a small amount of noise (Photoshop filter). The noise will not be seen but will create enough variation in color to prevent banding.