Preserving transparency and preparing to optimize

Next, you'll optimize the image in GIF format with background transparency and preview your animation in a Web browser. Remember that only the GIF format supports animated images.

1 Click the double-arrow button on the Optimize palette tab to expand the palette, or choose Show Options on the Optimize palette menu.

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2 Set the following options on the Optimize palette:

• For the color reduction algorithm, choose Perceptual.

• Select the Transparency check box (to preserve the transparency of the original image).

• For Matte, select white from the pop-up menu.

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3 On the Animation palette menu, choose Select All Frames.

4 Right-click (Windows) or Control-click (Mac OS) one of the frames in the Animation palette to open the Disposal Method context menu, and choose Restore to Background.

5 On the Animation palette menu, choose Optimize Animation. In the Optimize Animation dialog box, make sure that both the Bounding Box and Redundant Pixel Removal check boxes are selected, and then click OK.

6 In the image window, click the Optimized tab.

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ImageReady rebuilds the image according to the options you entered.

7 In the image window, click the 2-Up tab and compare the information for the original and optimized versions of the animated image.

8 Choose File > Save Optimized As, name the image Logo1.gif, and click Save.

If you want to preview your animation in the browser, you can do that now by clicking the Preview In Default Browser button on the toolbox. Then close the browser,

9 In ImageReady, choose File > Close to close the original file. Do not save your changes. You have finished your work on the fly-in logo.

For the Web: Setting the frame disposal method

The frame disposal method specifies whether to discard the current frame before displaying the next frame. You select a disposal method when working with animations that include background transparency in order to specify whether the current frame will appear through the transparent areas of the next frame.

The Disposal Method icon indicates whether the frame is set to Do Not Dispose or Restore to Background. (No icon appears when the disposal method is set to Automatic.)

• Choose the Automatic option to determine a disposal method for the current frame automatically, discarding the current frame if the next frame contains layer transparency. For most animations, the Automatic option yields the desired results and is, therefore, the default option.

Note: Choose the Automatic disposal option when using the Redundant Pixel Removal optimization option, to enable ImageReady to preserve frames that include transparency.

• Choose the Do Not Dispose option to preserve the current frame as the next frame is added to the display. The current frame (and preceding frames) may show through transparent areas of the next frame.

To accurately preview an animation using the Do Not Dispose option, preview the animation in a browser.

• Choose the Restore to Background option to discard the current frame from the display before the next frame is displayed. Only a single frame is displayed at any time (and the current frame will not appear through the transparent areas of the next frame).

-From Adobe Photoshop 7.0 online Help

The disposal options—Restore to Background O) and Automatic—clear the selected frame before the next frame is played, eliminating the danger of displaying remnant pixels from the previous frame. The Do Not Dispose ( °) option retains the frames. The Automatic option is suitable for most animations. This option selects a disposal method based on the presence or absence of transparency in the next frame and discards the selected frame if the next frame contains layer transparency.

In addition to the optimization tasks applied to standard GIF files, several other tasks are performed for animated GIF files. If you optimize the animated GIF using an adaptive, perceptual, or selective palette, ImageReady generates a palette for the file based on all of the frames in the animation. A special dithering technique is applied to ensure that dither patterns are consistent across all frames, to prevent flickering during playback. Also, frames are optimized so that only areas that change from frame to frame are included, greatly reducing the file size of the animated GIF. As a result, ImageReady requires more time to optimize an animated GIF than to optimize a standard GIF.

The Bounding Box option directs ImageReady to crop each frame to preserve only the area that has changed from the preceding frame. Animation files created using this option are smaller but are incompatible with GIF editors, which do not support the option.

The Optimize by Redundant Pixel Removal option makes all pixels in a frame that are unchanged from the preceding frame transparent. When you choose the Redundant Pixel Removal option, the Disposal Method must be set to Automatic, as in step 5.

0 For more information, see "Optimizing Images for the Web" in Photoshop 7.0 online Help.

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