Look at our sample image. Narcissus covers about 20% of overall area, inscriptions about 10% and approximately 70% of the picture are almost black. Why should we save all the image with equally high quality? Channel-based weighted optimization solves this problem.
1. Select Narcissus and the other key areas of the image with a selection tool.
2. In the Optimize palette, choose JPEG from the format menu.
3. In the Optimize palette, click the "Use a channel" 
button
next to the Quality slider (movie). A dialog box appears.
4. In the dialog box, display the Channel menu and choose Save Selection item to save the selected area as alpha-channel (movie). Note on the status bar of the image window how the file size has changed.
5. Set the quality with Maximum and Minimum sliders. The selected channel area will be saved with maximum, the rest of the image - with minimum quality.
6. Estimate the result. To tell you the truth, I expected more dramatic size reduction. However, even 5 Kb without loss of quality is not bad.
Now let's test the weighted optimization for GIF format:
Now test the weighted optimization for GIF format.
7. In the Optimize palette, choose GIF in the format menu. Set Colors to 256, color reduction algorithm to Selective.
8. There are 3 "channel" buttons on the palette now (screenshot). They make saved channel
to influence color reduction, dither and lossy settings. Use all these buttons
in the same way as with JPEG optimization.
Since 1999, Andrei has run the digiCollage – an online image editor's shop. Having edited all kinds of customers' images, he has vast Photoshop experience that he willingly shares with you in this course. You are invited to look over an expert's shoulder and see Photoshop in action.
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