To Use Masks To Modify Dithering; To Use Masks To Modify Color Reduction - Adobe PHOTOSHOP CS2 User Manual

Note: Lossiness is a reduction in quality; therefore, the highest level of image quality is defined by the Minimum value,
and the lowest level of image quality is defined by the Maximum value. This is the opposite of the JPEG quality setting.
6 Click OK.

To use masks to modify dithering

When you use masks to optimize the amount of dithering in a GIF, PNG-8, or WBMP image, white areas of the
masks yield the most dithering, and black areas of the masks yield the least dithering. You can adjust the maximum
and minimum levels of dithering in the Modify Quality Setting dialog box.
In the Optimize panel/palette, choose a GIF or PNG-8 setting from the Preset menu, or choose GIF or PNG-8
1
from the file format menu.
Click the Mask button
2
Choose which masks to use:
3
Uses the masks from all text layers in the image.
All Text Layers
Uses the masks from all shape layers in the image.
All Vector Shape Layers
Channel Specifies an alpha channel. (In ImageReady, you can choose Save Selection to create a new alpha channel
based on the current selection.)
4 To preview the results of the weighted optimization, select the Preview option.
Define the dithering range:
5
To set the highest percentage of dithering, drag the right (white) tab on the slider, enter a value in the Maximum
•
text box, or use the arrows to change the current percentage.
To set the lowest percentage of dithering, drag the left (black) tab on the slider, enter a value in the Minimum text
•
box, or use the arrows to change the current percentage.
6 Click OK.

To use masks to modify color reduction

When you use masks to optimize the colors in a GIF or PNG-8 image, white areas of the masks indicate to the color­
reduction algorithm which pixels are highly important, and black areas indicate which pixels are less important.
Thus, color is more greatly reduced in areas masked by black.
In the Optimize panel/palette, choose a GIF or PNG-8 setting from the Preset menu, or choose GIF or PNG-8
1
from the file format menu.
Choose a color-reduction algorithm and specify the maximum number of colors.
2
Click the Mask button
3
4 Choose which masks to use:
All Text Layers Uses the masks from all text layers in the image.
All Vector Shape Layers Uses the masks from all shape layers in the image.
Specifies an alpha channel. (In ImageReady, you can choose Save Selection to create a new alpha channel
Channel
based on the current selection.)
To preview the results of the weighted optimization, select the Preview option.
5
Click OK.
6
to the right of the Dither text box.
to the right of the Color Reduction Algorithm pop-up menu.
ADOBE PHOTOSHOP CS2
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User Guide