InDesign does
not use
vector gradients. InDesign as well as Illustrator use what is referred to as smooth shading, a feature of PostScript language level 3 and PDF 1.4 (and higher) to represent a gradient. What is stored in the InDesign document and subsequently in either PostScript or PDF is a numerical representation of how the gradient is supposed to look but not any specific rendering of same.
When displayed on a screen or printed to a non-PostScript or non-PDF device, these smooth-shaded gradients are rendered using Adobe's internal core technology graphics renderer. When printed to a device natively supporting PostScript language level 3 or minimally PDF 1.4, the smooth-shaded gradient by PostScript/PDF definition is rendered in a manner optimal for the particular device based on the device's resolution and available technology. Often, Adobe's PostScript and PDF OEMs go to great lengths to optimize this rendering for their devices.
As Peter noted, the gradient feather tool is effectively irrelevant to the smoothness of a gradient. It simply adds a dimension of variable transparency. However, taking a solid color from 100% opacity to 0% opacity using standard blending over a paper background could have a similar effect to that of having a 100% opaque gradient going from 100% tint to 0% tint, but not necessarily optimized for the device in question.
Gradients are always difficult in the sense that one is trying to translate a mathematical concept of a continuous range of color values into the real world of discrete color values, device resolutions, plate or toner drum characteristics, ink or toner characteristics, paper characteristics, etc.
One should always do printed, paper proofs of particular gradients to evaluate how they really will render prior to committing to same for layouts.
- Dov
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