You may remember I mentioned a few weeks ago that I was testing the 1ds files in a real life repro proofing test to decide what interpolating, sharpening and colour systems I needed to use in my workflow.
I now have the results back and as promised, to those who asked, here are my conclusions.
Working same size at 300 dpi I get a natural image size of 230mm x 345mm. This is easily big enough to cover A4 with cropping.
I enlarged the image in PS using 10% step interpolation and in GF. GF gave no appreciable gain over PS step so I abandoned it. I created an enlarged file of 515mm x 776mm at 300 dpi. I also tried enlarging in one step in PS and enlarging the original file to 225% in Indesign2.
Printing a small section side by side at 175lpi screen ruling I can see no discernible difference. What this means is that for litho print at this scale one doesn't need to use fancy interpolation methods. However, what is important in repro is the technique of sharpening. PS step and GF create a "smoother" image which can be used with some selective sharpening techniques to improve the way in which sharpening works on an image. But there are other sharpening techniques which can get close. If I were doing enlarged prints for display using an inkjet I would probably do step interpolation. One metre wide prints from the 1ds would be quite acceptable. I heard from several people that GF was best for subjects with straight lines in. At the size I was working to, 515mm x 776mm, this would not have become apparent. For litho reproduction at 175lpi GF and step interpolation would be unnecessary.
What is particularly interesting is the quality in the image enlarged 225% from the original without any upsizing.
As a side issue there was even less advantage in using step interpolation when downsizing.
With selective sharpening the appearance of the 1ds file gave better quality than medium format, fine grain film. The subject I chose was a medieval building in France with a small amount of sky. The digital file produced a smooth sky and smoother sharpening in the details of the building than film would have done. These are the two things we associate with photographic quality, smoothness in smooth areas and macro contrasts in detailed areas.
I used Capture 1 to process the images. The image chosen was shot in bright conditions using a fast shutter speed. There is no apparent camera shake and the detail is crisp.
The RGB to CMYK colour conversion is altogether more complicated. With the present controls converting to CMYK in Capture 1 does not seem possible if one wants optimum results. However it is within the realms of possibility to produce an RGB file which will then convert into CMYK in PS with reasonable success for most subjects. Settings of course depend on output.
Yours
Bob Croxford
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