Section 89. Change Color Depth

89. Change Color Depth

BEFORE YOU BEGIN

Just jump right in.

SEE ALSO

77 Convert Between Image Formats

78 Change Photo Resolution and Size

86 About Size and Resolution

One of the key factors affecting the size of an image file is the maximum number of colors it can include. If you're working on an image to be shared over the Internet, small file size is often a high priority. One way you can reduce a file's size is to reduce its color depth. Of course, reducing the number of colors in an image's palette can also reduce its quality because a limited number of colors are used instead of a full spectrum.

NOTE

A 16-million-color image might not actually contain 16 million colors, even though it is capable of doing so. Reducing the color depth for images that are generally monochromatic to start with might not appreciably reduce the quality but will shrink the file sizes considerably.

Because some commands are available only for grayscale images or for those that use 16 million colors, you might sometimes find yourself temporarily increasing an image's color depth. This won't, however, improve the resolution of a low-resolution imageincreasing an image's color palette simply makes more colors available for use; it does not tell PSP where to use them in an image to boost detail and clarity.

If file size is your main priority, you can compress an image into GIF, JPEG, or PNG format (for example), a process that also reduces its color palette a bit more scientifically than the method discussed here. You can also convert an image to grayscale to reduce its color depth.

TIP

If you're curious about how many colors your image is currently using, choose Image, Count Image Colors . To check the current color depth, look at the right end of the status bar.

1.	Display Increase/Decrease Color Depth Menu Choose Image, Increase Color Depth from the menu bar to increase the number of colors in an image; choose Image, Decrease Color Depth to reduce the number of colors instead.
2.	Select Color Depth Select the color depth you want from the menu that appears. If you're increasing color depth, the image is not changed, but more colors become available for you to use. If you're reducing the color depth, a dialog box appears, allowing you to choose how Paint Shop Pro will narrow the color palette and adjust image colors. Continue to step 3. 89. Change Color Depth
3.	If Reducing Colors, Choose Options and Click OK If you're reducing colors in an image, select how you want PSP to choose the colors for the palette by selecting options in the dialog box that appears. (The dialog box you see depends on which color depth option you selected in step 2.) Here are some choices you might encounterselect one of the following and click OK : Palette Component When reducing an image to two colors (black and white), you must tell Paint Shop Pro how to choose which pixels to change to white: based on their gray values, or their red, green, or blue components . Palette When reducing an image to 16 or 256 colors, use the Palette options to tell PSP how you want it to select the optimal range of colors for the image's palette. To select the most common colors used in the image, choose Optimized Median Cut . To choose the most common color in each of several small quadrants throughout an image, choose Optimized Octree . To make the image appear the same on a wide variety of computers, choose Standard/Web-safe . Reduction Method Select the method you want PSP to use to reduce the color palette: Nearest Color, Ordered Dither , or Error Diffusion . Choose Nearest Color to have PSP choose the nearest color in the color wheel when substituting an original color for a new color in the palette. Choose Ordered Dither to tell PSP to use a checkerboard pattern when working with two colors to create a blended color. Choose Error Diffusion if you want PSP to use a more random pattern when color blending with two colors. Because it uses a mathematical formula, Error Diffusion (when used in images with a very limited color palette) can sometimes generate artifacts in a color blended area, more so than using the Ordered Dither method. KEY TERM Error Diffusion Any of several mathematical techniques that attempt to compensate for large error values (differences between the intensities of an original pixel and its replacement in a reprocessed image) by dividing this difference into parts and distributing it to neighboring pixels, thus masking the obvious inaccuracy. Palette Weight This option appears only when you're reducing an image to two colors. Choose Weighted to balance out the color palette with an even number of light, dark, and medium tones. Choose Non-weighted to let the balance of tones in the image decide which colors belong in the palette. Boost Marked Colors By To use this option in 16 or 256 color images, select an area whose colors you want to favor, enable the Optimized Median Cut reduction method, and set a relative boost factor between 1 and 10. Include Windows' Colors If you intend to use the image exclusively within a Windows program such as PowerPoint, enable this option to include the Windows standard palette of 32 colors in the image palette. Reduce Color Bleeding As the Error Diffusion reduction method moves from left to right across an image substituting colors, a loss of color integrity might occur, with colors becoming too blended and more muted. Enable this option to prevent this from happening to your image.