Anti-aliasing and Resolution

The scale of anti-aliasing is tied to resolution. Holding all other variables constant, increasing the number of pixels in an image makes the effect of anti-aliasing more subtle. Let's take a look at an example of this phenomenon.

1. Open the file Linework2.psd from the CD (see Figure 1.8). This file is similar to the Linework.psd image you have been working on except Linework2.psd has greater resolution.

Figure 1.8

Line work with greater resolution

2. Zoom out to 25%. To do this, choose the Zoom tool in the toolbox or type Z on the keyboard. Hold down the Alt key on the keyboard and click the center of the image until you reach a magnification of 25%. This sizes the image in the Linework2.psd window down to a similar size as the Linework.psd window.

3. With the Linework2.psd window selected, choose Image > Image Size. There are 2000x1500 pixels in this image.

4. In the Image Size dialog box, uncheck Resample Image.

TIP Only use Resample Image when you want to change the number of pixels in the image.

5. Change the height to 6.25 inches. The width and resolution are automatically calculated from this number. The resolution is 240 pixels/inch. Click OK to close the dialog box.

6. Select the Linework.psd window, and choose Image > Image Size. This image has exactly the same document size, but its resolution is only 72 pixels/inch. Therefore, the pixels in Linework.psd appear more than three times bigger than the pixels in Linework2.psd.

Notice how the lines in Linework2.psd appear thinner and less jagged than the lines in Linework.psd. You perceive the lines to be smoother when the pixels are smaller. The lines on the left side of Linework2.psd (shown earlier in Figure 1.8) appear smooth, even though they are aliased, because of the higher resolution.

7. Close both Linework.psd and Linework2.psd.

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