The Image menu is enabled whenever you have an image window open in Screen Catcher. It allows you to view and modify characteristics of the image.
 
The first three commands in the menu modify the type of the image. These types are based on the way color is represented in the computer, and offer trade-offs between greater color accuracy and the amount of memory and disk space required to store the image.
Indexed
Indexed color images use less memory and disk space than 16 Bit and 24 Bit RGB images, but are limited to 256 or fewer colors. Choosing Indexed… will transform a 24 bit, 16 bit, or indexed image using one of several of palette and dithering options, as shown in the dialog below.
 
From the Palette popup menu, choose one of the following palettes. The available depths depend upon the particular palette you choose, as detailed below. Dithering can be used for greater reduction in the number of colors in an image, with some compromises in quality.
 
System: This palette maps all the colors in the image to the standard Macintosh system palette. Versions of the System palette are available for all bit depths (1, 2, 4, and 8 bits, representing 2, 4, 16, and 256 colors, respectively), so you can reduce color usage to the minimum necessary for your image. The System palette is useful if you want images to display uniformly across all color-capable Macintoshes without causing palette switching, or if you want to reduce an image for use as an icon or preview.
Grayscale: Like the System palette, the grayscale palette is available in 1, 2, 4, and 8 bit versions. It is useful for converting images for better reproduction on some black and white printers. With some images, it can also help minimize memory and disk requirements while retaining a better appearance and more information content than mapping to a color palette.
Windows®: This palette contains the 20 standard colors used in Microsoft Windows, plus a distribution of other colors that map well to a large number of images. The only depth available is 8 bits (256 colors).
Web: Netscape Navigator and Microsoft Internet Explorer use a standard 216-color palette when running on displays supporting only 256 colors. Converting all web graphics to use this palette will ensure that colors will display properly in most viewers' browsers, rather than the image looking dithered or "colorized". This palette requires a depth of 8.
Best: When you select this option, Screen Catcher analyzes the image and determines the optimal selection of colors for the palette. If you have an image with many shades of blue, for example, the resulting palette will be heavily weighted toward the blues, and will not contain any colors that are not present in the image. This option creates the smallest, best looking color palette possible, and is available for all bit depths.
16 Bit RGB and 24 Bit RGB
16 bit and 24 bit RGB images can contain thousands and millions of colors, respectively, but will take more memory and disk space than indexed images, which must contain 256 or fewer colors. Choosing the 16 Bit RGB and 24 Bit RGB converts the image to the indicated type. When downsampling from 24 bit to 16 bit, colors are remapped to the closest available 16 bit color.
Get Info
The Get Info command reports on the size, color content, and memory requirements of the image in the frontmost window.
 
The figures listed under Memory Usage indicate how much memory is required for Screen Catcher to display the image in a window. The When Active value indicates the true size of the image. The When Inactive number indicates how much memory Screen Catcher needs for the image if the Keep all images in memory option is turned off in the preferences, allowing the image to be swapped out to a temporary file on your hard disk to conserve RAM.
