You may have heard about “printing to grey balance”, but why is this so important?
If you’re printing to grey balance, everything is reproduced in the correct colour. If you’re not in grey balance, then you have a colour cast. This means that the printing has a magenta, yellow or cyan cast or any combination of these colours either across the whole tonal range or in the highlights, mid-tones or shadows.
So what does this mean in practical terms?
It means that the press operator will need to adjust his ink density to compensate for the cast. Why ink density? Well, that’s about the only adjustment the press operator can make – more ink, less ink. That’s it! The press operator is stuck with the size of the dots on the plate so the only way he can change dot gain is by ink density adjustment.
But as soon as he does that, the press is printing at a density which is higher or lower than the correct solid ink density. The correct SID would have been established at a Press Fingerprinting and Tone Reproduction Curve generation session. This would have established optimum ink density settings for correct colour reproduction on press.
What are the effects of using incorrect densities?
The ink density is linked to the volume of damping. This is generally called ink / water balance. If this balance is incorrect, the potential problems range from ink emulsification to bulls eyes, hickies, picking, lack of print contrast, reduced running speed, increased spoilage, and other undesirable issues.
Why does the printed sheet have a colour cast in the first place?
If the original file and subsequent contract proof are correct then usually the blame can be laid at the inaccuracy of the Tone Reproduction Curve or Plate Curve. If the size of the dots on the plate is wrong, it’s impossible for the press operator to match the proof for colour without adjusting the ink densities and inviting the range of problems listed above.
Is there an easy fix?
Absolutely. There are solutions on the market which generate dot gain compensation curves. Some of these are very sophisticated having been created with mathematical algorithms which produce smooth, accurate curves. Others are often the cause of the issues rather than the solution.