Our church has a monthly magazine, produced on our photocopier. Sadly, the photographs come out all muddy, with exaggerated contrast.

Yes, that is correct. Photocopiers will darken an image significantly, and will not work with images that are not already halftoned.

Does
anyone know of a Photoshop way one can prepare the pictures so that they will be more acceptable to use with a photocopier?

Being a veteran of small-press publishing, this is an area where I've had a lot of practice. :)

For good quality photocopiers, you should use an 85-line halftone screen for your images. A tighter screen will reduce the number of shades of gray your image will have, especially on a 600 dpi printer, and will not photocopy as clearly.

Very, very important to photocopy reproduction is the quality of the image going in to the process. Photocopying introduces significant "dot gain" into your images; what that means is that photocopied images become much darker.

To get good results when reproducing an image on a photocopier, you must get familiar with Photoshop's Curves command. This command is found under Image->Adjust->Curves. You also must have your Info palette open and be familiar with how to read the numbers in it.

Start with a grayscale image. Set your Info palette so that one of the two readouts displays "actual color." Open the Curves window (Image->Adjust->Curves).

Since photocopying darkens an image, you are going to lighten it. It should look too light and slightly washed-out on your screen. If it looks perfect on your screen, it will look muddy and dark when you photocopy it.

First, position the mouse pointer over the darkest part of the image which still contains detail. This part of the image should not be 100% printing according to the Info palette. Instead, it should be no more than about 85% printing; the shadows in your image will darken dramatically on the photocopier.

If the darkest shadow detail in your image is darker than 85%, pull down the shadow end of your curve (the right-hand part of the curve in the Curves dialog) until your Info palette shows it to be about 85%.

Now look at the lightest part of the image which still contains detail (not the part which should print pure white; the lightest part that shows detail). It should be 5-6% in your Info window. If it is lighter than this, that part of the image will be pure white (no detail) on the photocopier. If it is darker, lighten it by moving the left-hand point on the curve to the right until the Info palette shows you it is about 5-6% printing.

Now pull the middle of the curve down slightly.

The image will look much lighter on your screen. This is what you want.

Click OK in the Curves dialog. Now print the image to your laser printer, using an 85-line halftone screen. Your results when you photocopy should be much better.

Note If you are not using a PostScript printer, then you probably have no control over the printer's halftoning. All images printed on something like a black and white printer or a printing press must be "halftoned," because such devices are incapable of printing shades of color or grey; look at a newspaper with a magnifying glass and you will see that shades of grey are simulated using patterns of dots, called "halftone dots," which create the illusion of tones.

Cheap personal laser printers that do not use PostScript can't usually control the kind of halftone they create, and the printer's default halftone is not appropriate for photocopying.

If you are using a laser printer that is not PostScript, then you can create the halftone in Photoshop. Use Image->Mode->Bitmap; in the dialog box, choose 1200 dpi as the output resolution, round dot halftone, 85 lines per inch. This will create a bitmap file which you can save with a different name and print to your laser printer.

Printing a halftone to an inkjet printer will deliver exceptionally poor results; you should not try to create a master page for photocopying using an inkjet printer.

Hope that helps!
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Reproducing photographs on a photocopier