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Lesson 16. Optimizing Web Images > Choosing basic optimization settings in Imag...

Choosing basic optimization settings in ImageReady

Earlier in this lesson, you used Photoshop optimization settings that were integrated into the Save For Web dialog box. In ImageReady, the same options appear in the Optimize palette.

In ImageReady, choose File > Open, and open the 16Start2.psd file from the Lessons/Lesson16 folder.

This image was created in Adobe Illustrator, and then rasterized into Photoshop format. The image contains many areas of solid color.

Click the 2-Up tab in the image window.

The optimized version of the image is selected on the right side of the window.

In the Preset pop-up menu on the Optimize palette, choose GIF 128 No Dither.

If necessary, click the arrow to expand the Color Table options on the Optimize palette, and then select Perceptual on the Reduction pop-up menu.

Selecting a color reduction algorithm

One of the ways to reduce image file size is to reduce the number of colors in the image. Photoshop can calculate the most needed colors for you, based on any of several available algorithms. You specify which algorithm is to be used by making a selection from the Color Reduction Algorithm menu, which includes the following options:

Perceptual Creates a custom color table by giving priority to colors for which the human eye has greater sensitivity.

Selective Creates a color table similar to the Perceptual color table, but favors broad areas of color and the preservation of Web colors. This color table usually produces images with the greatest color integrity. Selective is the default option.

Adaptive Creates a custom color table by sampling colors from the spectrum appearing most commonly in the image. For example, an image with only the colors green and blue produces a color table made up primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum.

Web Uses the standard 216-color color table common to the Windows and Mac OS 8-bit (256-color) palettes. This system ensures that no browser dither is applied to colors when the image is displayed using 8-bit color. (This palette is also called the Web-safe palette.) If your image has fewer colors than the total specified in the color palette, unused colors are removed.

Custom Preserves the current color table as a fixed palette that does not update with changes to the image.

Windows or Mac OS Uses the system’s default 8-bit (256-color) color table, which is based on a uniform sampling of RGB colors. If your image has fewer colors than the total number specified in the color palette, unused colors are removed.

The status bar at the bottom of the image window displays the view magnification and other useful information about the original and optimized versions of the image.

A. File size and download time of optimized image B. File sizes of original and optimized images

You can customize the type of information that appears here.

In the status bar, choose Size/Download Time (56.6 Kbps Modem/ISDN) in the middle pop-up menu, and then choose Image Dimensions from the pop-up menu on the right.

The 56.6 Kbps is usually more common now than 28.8 Kbps. The dimension displays the size of the image in pixels, which is important to know when planning how to fit an image into a predesigned Web-page template.



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