The Color Bar – Part 1 of 4 – Background

Color bars (a.k.a. color control bars, color control strips, or proofing bars) are essentially test targets that are used to measure print and/or proof attributes. Normally, but not always, it is printed in the trim area of the press sheet.Typical placement of a color bar on an offset press sheet - at the trailing edge (back end of the sheet).
However, it can take many different forms - sometimes hard to recognize - but always serving the same purpose.

Sometimes the "color bar" is incorporated within the graphic design of the publication. In this case the color makeup of the title (Cyan) and section headers (Blue, in this example, - Magenta overprinting Cyan).
Sometimes it is hidden in the spine (in this case the grey line running from top to bottom on the front edge of the photo).
While it is certainly possible to measure the color of the actual live image area, the technology is expensive and, as result, few printers are fortunate enough to have it at their disposal. Also, measuring the live image area doesn't provide as much useful information as a color bar can. Color bars therefore act as proxies, or substitutes, for the live image area as well as provide additional data.

The logic behind color bars

1) Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.

2) Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.

3) Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.

4) Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.

5) They can be used forensically to help understand why a specific job did not meet expectations.

6) They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.