IN-DESIGN VS. PHOTOSHOP
I went to a client-site a few years ago to help choose photos for a poster. I was surprised to learn that the client always laid out her posters in Photoshop. I, on the other hand, had always laid out my posters in Quark XPress. I had assumed Photoshop was only for editing images, not laying out pages. I was confused, so I decided to do some research.
One printer with whom I spoke said it was perfectly fine to create a poster in Photoshop. He even said that PostScript RIPs easily processes the resulting TIFF files when producing film or plates. The printer did, however, encourage me to put the type on the vector layers and use sufficient resolution to provide crisp type edges when the file was finally rasterized (turned into bitmaps for printing).
I also asked the printer about creating posters in Adobe Illustrator. I learned that designers usually don’t create posters in Illustrator, but they do use Illustrator for packaging design. Apparently, Illustrator is ideally suited to producing the irregular shapes--tabs, folds, etc.--of the flat sheets that will be subsequently die-cut, folded, and glued into product packaging. Again, the PostScript RIPs can process these files without incident.
When, then, should designers use page composition applications such as InDesign and Quark?
First of all, multi-page documents are perfectly suited for Quark and InDesign, and not for Photoshop. Both the poster and the product packaging mentioned above were single-page documents, unlike books or booklets. Text-heavy documents also fit into this category, whether or not they are multi-page documents, because both InDesign and Quark have robust text processing features. For instance, if you want to easily flow text from one column to another, InDesign and Quark work far better than Photoshop. The same is true if you want to use style sheets for formatting type.
Finally, although it is quite possible to produce posters in Photoshop (and my client was doing so quite successfully), the monitor will repeatedly render the high-resolution images every time you make an adjustment in Photoshop, and this re-rendering takes a lot of time. In a page-composition application like InDesign or Quark, you can adjust the text and vector art without re-rendering the background bitmapped images, thus speeding up your workflow.
DESCREENING VS. COPYDOT HALFTONES
What can you do if the only photograph you have to work with is a previously screened halftone, for example an image from a printed magazine or book? Two years ago in Quick Tips, I suggested one solution, which I will repeat below. This year, I have added two new work-arounds.
First off, if you do nothing but scan the image, which has already been broken down into a screened pattern of halftone dots, and then screen it again when you prepare the film or send the job to the platesetter, you may very well end up with a moiré pattern.
Moiré is an extra, unwanted patterning created when you superimpose one screen over another. You can see this effect by laying one window screen over another and rotating the top screen. At a certain point, you’ll see arcs and loops in the combined screen pattern.
To avoid moiré patterns when using a previously screened image, your first option is to descreen the image. To do this, open the image in an image editing program like Photoshop, and then apply the descreen function (or Gaussian blur), which blurs the image (and the halftone dots). When you sharpen the image again, the dots won’t be visible. (Hint: Start with a very large image and then reduce its size as you complete these steps.)
Another way to avoid moiré is to set the new halftone screen to an angle different from that of the initial screen applied to the photograph. The angle between the two halftone screens must be at least 30 degrees. (This is actually why 4-color images usually don’t have moiré problems, since the cyan, magenta, and black halftone screens are all set 30 degrees apart—and the yellow screen is set at a smaller angle, since it is the least visible color and hence is more forgiving.)
The third option is to reproduce the screened halftone “dot for dot.” This process yields a “copydot halftone.” Basically, in this solution you reproduce the previously screened halftone as line art: that is, without a halftone screen. In this case, the only screen used is the one in the image with which you started. (This is not a good idea if you plan to enlarge the image, because the halftone dots will become more visible. Reducing the image size is less problematic; although, if the dots get too small and close together, your halftone screen will plug up.)
Keep in mind that all three solutions are art, not science. Therefore, you should plan to experiment a few times to achieve success.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]