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Chapter 5. Optimizing Grayscale Images > Preparing for a Printing Press

Preparing for a Printing Press

Take a close look at the black-and-white image in Figure 5.26, and imagine that you took that image to Kinko's and made a copy of it. Then you took the copy and copied it again at your local library. Then you took the library copy and ran it through the copy machine in your office. Then you held the version that had been copied three times next to the original. Would you expect them to look the same? Of course not. In fact, the tiny dots that are in the brightest part of the image would have begun to disappear and become pure white, because every time you make a copy, you lose some quality. Well, the same thing happens when you hand over your image to a printing company. When you give your printing company your original output, they will have to make three copies of it before it makes it to the end of the printing process. They start by converting the original into a piece of metal called a printing plate, to make the first copy. Then they put the plate on a big, round roller on the printing press and flood it with water and ink. The oily ink will stick to the plate only where your images and text should be; the water will make sure it doesn't stick to the other areas (using the idea that oil and water don't mix). Next to that roller is another one known as a blanket; it's just covered with rubber. The plate will come into contact with the blanket so the ink on the plate will transfer over to the blanket—that's your second copy. Finally, the blanket will transfer the ink onto a sheet of paper to create the last copy (Figure 5.27). Each time a copy is made, you lose some of the smallest dots in the image. Until you know how to compensate for this, you're likely to end up with pictures of people with big white spots in the middle of their foreheads.

Figure 5.26. Copy this image three times and you'll lose detail in the brightest part of the image. (©2005 Ben Willmore)



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