Product

Platform

Operating system

Error

Symptoms

Symptoms: Colors on a page can appear darker in different page positions on the same imposition, especially when there are different colors near the different page positions. That is: evident in areas of gradations or images containing light to dark transitions and most notably with adjacently positioned pages containing areas of light to dark gradations.

There appears to be a color variation between multiple copies of the same artwork on an N-up layout (particularly involving gradients and shading.)

For example: An operator places a single PDF which contains horizontal light to dark gradients 2-up in an imposition, which are positioned exactly next to each other on the imposition with the light part of one page’s gradient being next to the dark part of the second page’s gradient.

Operators expect that the output of the two pages be exactly the same, yet perceive a darkening in each separation on one of the assigned pages.

Cause

(Google search: “retina and lateral inhibition� and “Lightness Perception and Lightness Illusions� ).

Solution

How to disprove the color shift or differences:

1. Reposition the page in a different location in the imposition

2. Compare the pages by trimming or cutting out one of the pages from proof or plate and placing side-by-side or top to bottom depending upon image. Operators should now note no differences between the pages.

3. Render 1BitTIFF of a particular separation where the alleged difference is most obvious and overlay both pages on 2 different channels in Photoshop or Copydot Toolkit; the half-tone dots should be exactly the same size.

4. Measure the proofs or TIFF output with any of spectrophotometer, CopyDot Toolkit’s tint tool, or Photoshop’s “eye dropper� tool. In doing this, it’s important to ensure you’re measuring the exact same part of the image on both instances of the page.

Approaches you can use to ensure this are:

a. Taking note of coordinates on each page to ensure accurate readings

b. Overlay a visual grid onto the page (using the original source file, or Pitstop, etc.) to ensure you measure the same point on both instances of the page

c. Downsample the page to a lower resolution (example, 10 dpi) so it’s easier to identify/measure specific pixels within the image.

Permanent fix:

See also

Keywords

color, imposition [layout], output

Technical contact(s)

Malcolm Kenning

Submitted by

Malcolm Kenning

Date submitted

05 Jun 2006