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What’s in a Pixel?
Creating excellent scans that work for your projects is all about resolution. And, resolution boils down to pixels.Here’s a quick pixel refresher. Pixels are the tiny colored dots that, put together in an orderly grid, make up a Photoshop image. The display on your computer monitor is also made up of pixels. The number of screen pixels on your monitor depends on the display setting you’re using. For instance, a typical setting is 1024 x 768, meaning 1,024 pixels run across the screen and 768 pixels run down the screen. Multiply them together and you get . . . well, you use a calculator. These screen pixels are so tiny that you may not be able to see them even if you flatten your nose to the screen.To get a look at image pixels more closely, open an image in Photoshop and magnify it to 200%. (For a refresher on zooming and magnifying images, turn to Technique 5.) At 200% magnification, image pixels are magnified to four times their previous size. One image pixel now measures two screen pixels wide and two screen pixels high and 2 x 2 = 4. Next, magnify the image to 400%. That single image pixel is now magnified to sixteen times its original size and measures four screen pixels wide and four screen pixels high (4 x 4 = 16). Take a look at Figure 10-1 to see how different magnifications affect the appearance of image pixels on-screen.
Figure 10-1: Increasing the magnification makes an image appear larger on-screen but doesn’t affect the printed image.
Magnifying an image in Photoshop has nothing to do with the size at which an image prints — it only affects how the image looks on-screen. To view an image at its approximate print size, choose View>Actual Pixels.The quality of the way an image looks on-screen and on a printed page depends upon the resolution of the graphic.Images scanned for the Web need to be a resolution different from images scanned for the printed page. A typical PC monitor resolution is 96 pixels per inch (on a Mac, it’s 72 ppi); this low resolution creates small file sizes and images that work well for the Web. If I print an image set at 96 ppi, it looks very pixilated, as shown in Figure 10-2. The higher the resolution, the finer and sharper a printed page looks. A typical printed image is set at 300 ppi. Many home and office printers offer resolutions upwards of 720 ppi or even 1200 ppi.
Figure 10-2: Check out the pixels: 96 ppi (top), 150 ppi (left), and 300 ppi (right).
When you scan an image, you can use the scanner’s software to set the resolution of the scan. Know what you are using the scanned images for — the Web or print — and set the resolution accordingly.
