Gernot:

Your PDF is interesting though the math is beyond me, as it is with most I fear.

Yet it speaks of an important issue, namely the screening of very high resolution raster images, specifically as it relates to rendering very fine type. And here I am thinking: product shots.

Conventional wisdom states that you should work in 300ppi for offset printing, or 2x the screen-ruling for optimal results. One also hears that smaller amounts like 1.8x screen ruling is sufficient.

And the same rules would have you work as close to final size as possible, avoiding scaling in a layout application (a rule that not many actually follow).

So if you worked in 4x your final size @300ppi and reduced everything 25% in your layouts, you would effectively send 1200ppi to the printer. A real no-no right?

In the case of very small type, the digital screening process would map this type between the halftone dots so to speak, and said type would hold up under magnification with a loupe very well. The same size type prepared at 300ppi final size would probably be comparable to the naked eye, but upon magnification would not be readable at all, just as zooming up in Photoshop would reveal mush.

Similarly, the same size image produced the old way through a halftone screen, would also be way-broken-up by the halftone dots, so this illustates the advantage of digital screening.

Of course, the type of rip which handles this type of imagery has a lot to do with the outcome. A CT/LW (ScitexCreo) type of rip, which reinterpolates all rasters, would destroy all that extra resolution, so you would be no better off than if you worked 300ppi at final size. But a rip which generates screened plotter files from the print requests would show this benefit.

Now don't get me wrong. I'm not advocating working at an effective rez of 1200ppi for everything. That would be idiotic. Just small product shots, and books... things that you scan or shoot and you have a lot of them, and the idea of replacing type elements with vector type is prohibitive.

Then there is a bigger question that needs asking: Is it worth it to store, and print all that extra data to improve the readability of type which can only be read under high magnification? Answers will vary on that one. My answer has always been, "No, it's not worth it, that type is not meant to be read anyway". But now I don't know, it's kind of like keeping everything in 16bit. Even though nobody else can easily see the difference, you somehow feel better holding on to that difference.

Marcia_Ripatte

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