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December 17, 2013 Printing Techniques & Tips

Working With Process Color Curves For Uncoated Paper

curves comparison

The image resolution, proofing, printing press, paper and communication process surrounding a project will all influence the reproduction quality.

Communication is key for determining the best approach for printing four-color process on uncoated paper, especially since printers work with many different workflows. Many larger printing companies prefer RGB files and operate with a standard set of “uncoated curves.” They often have a technical staff to support color corrections and to optimize images for uncoated papers.

These practices vary from smaller printing companies who have limited ability to make color adjustments and custom curves. These printers encourage designers to submit a converted CMYK file which includes the final color adjustments.

Making the adjustments for color reproduction on uncoated papers requires a basic understanding of dot gain. Dot gain is the term used to describe the halftone dot’s natural spread when the ink is transferred to the paper’s surface and spreads a little. It is somewhat like watercolor paints but not to that extent.

If nothing is done to compensate for dot gain, the images can look over-saturated and lacking detail, as shown in the image to the left above. Dot gain will impact the mid-tones and three-quarter tones the most. Slightly shrinking the dots on the printing plate will resolve these issues as more white space is “opened up” for the ink spread.

The Adobe Photoshop “Curves” dialogue box can be used to compensate for dot gain on uncoated papers. Because the curves adjust the density of an image, it is an excellent tool for resetting the value of mid-tones while keeping a smooth, consistent line from the highlight to shadow area.

In general, the dot size of the mid-tones and three-quarter tones are reduced by 12-15% to allow for the inherent dot gain on uncoated papers. The image to the left in the comparison at the top of the page has not been adjusted for uncoated paper and demonstrates where dot gain hurts the most.

curveTo improve these results, color curve adjustments need to be made. Looking to the right, the Photoshop curves dialogue box is 10 grid units by 10 grid units. The red dot represents the three-quarter tones. By moving this dot to the right of the default setting, just over 1 grid unit, the density will decrease by 12% (representing a 12% decrease in dot size). The blue dot represents the mid-tone area at 50%, and is moved 1.5 units, lowering the density of the mid-tones about 15%. These adjustments preserve the brightest highlights and the darkest shadows. It is important to maintain a smooth arc in the curve to keep the gradation in the image natural.

Keep in mind, this is a single demonstration and should only be used as a guide.

Order the Finch Process Curves for Uncoated Paper reference tool here.

 

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