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8 Resolution and Scanning > Scanning previously printed images - Pg. 103

ResolutionandScanning 103 Scanning Previously Printed Images If you are sent an image that has been printed using the four-color process and that you are now supposed to scan, you have two problems. The first is copyright. Does the client have the right to use this image? Check up. Otherwise, you may be liable. The second problem is that all the correct screen angles for the CMYK colors have already been taken (see Chapter 2). If you simply scan the print again, the result will be a moiré pattern. This is because as your scanner moves across the image, it captures whole rows of pixels at a time, each one of which is called a "sample." The number of samples per inch (SPI) is therefore the same as the number of dots, or pixels, per red looks better, and so does the green, but there is still a strong moiré in the blue channel. Now look at the second set of individual channels, which is how things look when the image is converted into CMYK. As you can see, while the C, M, and K channels are much improved, there is a strong moiré in the yellow--however, as previously discussed, the special quality of this color means we see the yellow but we do not see the grid, and therefore the moiré it produces remains invisible. So the moiré in the blue channel in the RGB version becomes the moiré in the yellow channel of the CMYK version--which means that the blue moiré is just as invisible in the RGB image as the yellow moiré is in CMYK. Yet blue is visible and the moiré