Reply To: InDesign/Prepress Myths

I want to back up Mark G. in one thing: Yes, I do believe that in certain situations, on certain RIPs, and with certain images that have sharp edges, higher resolution does result in what he calls a combination tone. In fact, this came up in the very first edition of my book “Real World Scanning & Halftones.” Some images, when printed as halftones, do appear to be a combination of vector and halftone artwork. That is, there are printer dots where there shouldn't be (between halftone spots).

I actually showed this to Chuck Geschke (one of the inventors of PostScript) and, if I recall correctly, he thought it was likely a bug in the halftone algorithm. That said, it does turn out to be useful because it gives a better illusion of edge detail where the halftone would ordinarily have trouble with it.

So Mark isn't crazy! But I agree with everyone else (and my earlier comments) that increasing resolution as a general practice, or even when you have these kinds of images, is not the best technique. Reasons:

• If it's rasterized, you probably don't have control over what's going to happen downstream (how do you know it's not going to get downsampled by the rip, the software, a person, etc.)?
• It's just plain easier and more straightforward to save as PDF. True, your file may be rasterized by some moron downstream, but at least you can argue that it was vector and they screwed it up. If you provide pixels, you can't argue with them.
• The “bug” of “combination tone” is not guaranteed on all RIPs. Again, halftone output should not exhibit printer dots between the halftone spots, so the fact that you're getting them is a lucky accident.
• Your file sizes are way bigger than they need to be. I just made a document with only text and vector shapes in it; it was 7 MB at 300 ppi tiff; 58 MB as an uncompressed 900 ppi tiff; 3.2 MB as an LZW compressed 900 ppi tiff; but only 188 K as a PDF. (Or 510 K if I included the psd data to make it editable in the future, which the rasterized tiff would certainly not be.)

I hope that helps!