Is Gradation Still an Issue in Digital Print?
By Heidi Tolliver-Walker on April 4th, 2014
I ran across this discussion in one of the digital print groups on LinkedIn this morning and thought it was interesting. I wonder what you folks think here. What are your experiences?
The original question was why the member was having trouble with gradations on his digital press. The discussion was highly technical and beyond what is appropriate to reprint here. However, among the potential culprits named in the discussion were the following:
- Line screen
- Different resolutions based on XY axis, i.e. 2400 x 600 dpi (especially on older presses)
- Dot size and shape
- Level and frequency of calibration of the press
- RIP interpretation of the data (and, consequently, the age of the RIP)
- Age of the digital press
- Whether the press is using standard elliptical halftone dots
- Whether stochastic screening is used
- Trade-offs in recording resolution and speed of production
- Whether color curves are calibrated to match the offset press and stock
One participant suggestion: Use a Gaussian blur. (“Best gradations ever.”) Another posted a link from Adobe (“Illustrator / printing gradients, meshes, and color blends“) that breaks down all the potential issues to help with troubleshooting gradient issues.
One participant noted:
Gradation in digital printing is not appearing like offset because of the physical resolution of the technologies you compare. Standard offset reproduction of the image is 2400 dpi arranged in 150 lpi. This is how the RIP is setting the image before physical reproduction by the imagesetter on the offset printing plate and then by the printing press onto the substrate. This standard RIP setting gives a visually smooth image for the human eye when printed because these settings guarantee reproduction of all 256 grades/tones used by the RIP to reproduce the picture. Remember the RIP uses the rule of 16 x 16 = 256 for calculating grades/tones. Offset technology can go to a sharper image with, for example, 4800 dpi (smaller dots) and 300 lpi. Even 9600 dpi and 600 lpi is possible. Only on the condition that dpi is increased proportionally with lpi will you reproduce all 256 grades/tones to see a smooth image at the end. That means you will see a sharp or very sharp picture with smooth gradation only when increase dpi together with lpi. (Lightly edited for clarity.)
What are your experiences? Are you still having gradation issues in your jobs? If so, which of these do you see as the culprit(s) most of the time? How do you handle these issues?