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Lesson 16. Optimizing Web Images > Adding dither to simulate missing colors

Adding dither to simulate missing colors

Before you begin this procedure, make sure that the Optimize palette still shows Perceptual as the Reduction option and 128 for Colors. In the canyon image, notice the gradient brown bands in the cloud. You’ll be focusing on this portion of the image and the aspen shadows as you make adjustments in this topic.

Under Dither in the Optimize palette, select Diffusion on the Method pop-up menu and drag the Amount slider to 100%.

Now a speckling pattern softens the transition in color in the cloud area. Any change in the aspen area is either not noticeable or more subtle.

Reselect 32 as the Colors option.

The aspen image looks arguably even worse than before. The area that had been dark green now appears as a speckling of dark brown on a medium green. The clouds in the canyon area look smoother, but the skies over the canyon and mountain images—both of which used to be uniform colors—are now speckled.

Drag the Dither slider to 50%, and then experiment with other dither percentages.

ImageReady minimizes the amount of dither in the image, but no percentage of dither will preserve the drop shadows without ruining the green background. Also, reducing the percentage of dither reintroduces the multicolored striping in the clouds above the canyon.

Set the dither back to 100%.

Reset the Colors option to 128. (Leave the dither settings as they are.)

The aspen shadows turn dark green again and the speckling is not noticeable. But while the file size is smaller than the original (unoptimized) version, the optimized version is a little larger than it was without dithering. You have more work to do in optimizing this file, so go on to the next topic.



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