When migrating from NexusRIP or FlexRip to Imaging Engine, what differences will I see in the rendered output?
Graphical elements in a PDF file (such as a filled shape, character glyph or sampled image) are converted to pixels by a process known as Scanconversion. Given a mathematical description of the graphical element, this process determines which pixels to adjust and what values to assign to those pixels, to achieve the most faithful rendition possible at the available device resolution.
The process for filled or stroked shapes, character glyphs and images are all slightly different. For instance, filled or stroked shapes are scan converted using a purely mathematical basis, whereas character glyphs typically contain extra information that can control more precisely which pixels are filled at when rendered at different font sizes and resolutions.
Filled or stroked shapes
The Scanconversionmethod used by Adobe® is that a pixel is filled if any part of it is mathematically inside the shape. However, in FlexRip the rule is slightly different: here a pixel is filled only if its centre is mathematically inside the shape. The result in FlexRip output is that, rendered shapes are on average 1 pixel smaller in each dimension compared to Imaging Engine Powered by Adobe®.
NexusRIP uses the same rule as Adobe® so Nexus users should expect very similar results from Imaging Engine.
The following diagram shows the difference between the FlexRip and Adobe® scan conversion rules. The text character has been converted to line art and rendered in both RIPs. The red pixels in the comparison window on the right shows the extra pixels that are filled by Imaging Engine.
The size of the enclosed space at the top of the outline becomes smaller. In the same way that rendered shapes are on average 1 pixel bigger in Imaging Engine output compared to FlexRip, holes in rendered shapes are on average 1 pixel smaller.
At the high resolutions typically used for CTP work, these differences are very small and typically will not be noticeable. However, at lower resolutions the difference could become important especially for objects such as bar codes. In this situation we recommend that the output is checked and any bar width reduction parameters in the front end application are reviewed.
Neither FlexRip nor NexusRIP make use of font hints, but Imaging Engine does. This should result in improved typographical output from Imaging Engine when compared to the legacy RIPs, especially at lower resolutions.
In FlexRip, the scan conversion rules mean that the weight of character glyphs is very similar whether they are converted to outlines or preserved as text. With Imaging Engine (much the same as NexusRIP), converting text to outlines will produce a result with a slightly thicker appearance and in addition font hinting information is lost. For best quality output we recommend that, where possible, text is preserved as live text. In particular, care should be taken in PDF creation to maintain consistent treatment of text so that glyphs converted to outlines are not mixed with ones preserved as live text. Mixing characters in this way can result in an uneven overall appearance of text, particularly at lower resolutions.
The scan conversion process for images is the same for all three RIPs, so the output should be very similar in each case.