How to obtain the best tints and gradients (vignettes/blends)
There is a tendency for banding (changes in density) on all electronic devices and this can give rise to undesirable artifacts in blends or areas of tint. It will very much depend on the color and its density since your eye is particularly sensitive to these changes in some colors. For example, you cannot easily detect changes in density in yellow or red but you can quite easily see changes in blue or green.
There is no magic formula to tell you if a color will be problematic but your Sales Rep should be able to advise you on this. As a guide colors that are difficult to print conventionally out of 4-color process inks will also be difficult to print on an HP Indigo digital press. There are however some guidelines and tips that you can use to minimize the appearance of banding. If you can, try to avoid using large areas of that particular color. Smaller patches will look better than large areas. Lighter tints tend to look better than heavier tints, but try to avoid specifying tints lighter than 5%. If you have a large area of a color that is proving difficult then either consider printing it as spot color (check with your SALES REP to see if this could be an option) or introduce some granularity into it. This can be done with most professional image editing software. Create an image with the actual physical size you need and fill it with the color you require and then add some noise (5–10%), a pattern or an image. This will help to smooth its appearance while maintaining the original color. The same tactics can be applied to blends. Blends can show banding and again it will depend on the colors in the blend. Best results are achieved when the tonal range is less than 50%. Shorter blends tend to be better than longer blends since the change in tone is less subtle. Similar to tints you could also generate the blend using an image editing software package and then add some noise.