Colour correcting is the adjustment of a scanned image's colour and density ranges to match that of the original image. This ensures that the colours and shadows/highlights in the printed image are as close to the original as possible.

Colour correction of images for printing on our coldset web press is done by adjusting the image's Dot Gain, GCR, UCR and Density, listed below.

DOT GAIN
Dot Gain is basically when dots increase in size as wet ink is absorbed by the paper. Many situations may cause dot gain to occur, paper type, type of press, duplication of film. In the end, dot gain causes colours to print darker.
Note: Cold-Set web printing on newsprint gains up to 15%. This needs to be allowed for in your scans. An 85% area in an image will gain up to almost a solid black on a cold-set web press.

Halftone dots in a grayscale proof

Halftone dots after printing

GCR, UCR
GCR (Gray Component Replacement) and UCR (Under Colour Removal) are both adjusted by the printer. You as the customer do not have to worry about it. These techniques replace certain amounts of cyan, magenta and yellow inks with black ink. GCR replaces all neutral colour areas with an appropriate amount of black, using only minimums of cyan, magenta and yellow inks. UCR is used to deepen shadow areas and neutral colours in images.

DENSITY
When adjusting your pictures in an image editing program such as Adobe Photoshop, using curves (Command / Control-M), and following the info palette, the density refers to how much ink goes to the highlights (lighter areas), midtones (mid-gray areas) and shadows (dark areas) of a picture. For our cold set web press we use a highlight of 3-4% dot and shadow of 83-85% dot maximum, midtones range between these percentages. These adjustments allow for dot gain on our press.

A typical scan before adjustments using Curves (Command/Control-M or Mode-Adjust-Curves) in Adobe Photoshop. This picture has the shadows at 100% and the highlights at 0%.

A typical scan after adjustments using Curves. This has lessened the density of the black, to around 85%, and ensured that the highlights have at least 3% dot in them.