HVS ColorGIF 2.0 User Manual

Palettes

Various palette modes can be selected from the Palette popup menu. These options determine how HVS ColorGIF will go about assigning colors to the image. Colors can be derived from an already-built color table (fixed) or they can be calculated by the HVS algorithm (Adaptive).

• Custom
  This mode is automatically chosen to indicate that a palette has been altered by the user (i.e. by deleting unused colors) but has not been saved. You can choose this palette mode explicitly if you want to preserve some of the existing colors in a palette, but want to reduce the overall color count. For example, you could start with the Netscape 216-color Fixed palette, but choose a color count of 64 in Custom mode. This would cause HVS ColorGIF to analyze the image and the target palette and preserve only the 64 best colors to represent the image at the current dithering intensity.

  This option can be a powerful tool for reducing the size of an existing GIF. Try downloading a GIF from the Web, opening it in Photoshop, and running the ColorGIF filter on it (be sure the GIF contains black and white or has less than 255 colors and convert to RGB). HVS ColorGIF will come up with the Exact palette enabled. If not already in Exact mode, select Exact from the palette menu then change to Custom, and try reducing the number of colors in the color table. Play with the dithering to adjust quality. You'll probably find that you can significantly reduce the size of most existing GIFs, even without access to the original 24-bit image, and without quality degradation! Of course, if the person who made the GIF is already an HVS Color user, they might have already pushed it as far as it will go. If you do have access to the original 24-bit image, by all means use it, because it will produce the best results.

• Adaptive

  This mode generates an HVS Color optimized palette using the current parameters. To allow the setting of adaptive palette parameters, an adaptive palette will not be generated until the user clicks on the Preview Button. An HVS Adaptive palette will produce the best color table for the image, but will take longer to calculate than dithering to a fixed palette.

• Exact

  This selection is enabled if the input image had 256 or fewer colors. When selected the number of colors actually present in the RGB image is displayed in the Colors Used status line, and the color table shows the colors in the image.

• HVS Multi

  Starts the MultiPalette creation process. A "Super" or MultiPalette factors multiple images into the analysis and generates the best color table for all the images. This is useful in multimedia development and for creating Global GIF animation palettes.

• Netscape
• System (Mac)
• System (Win)

  These selections dither the image to one of these preset fixed palettes. This could possibly leave some colors unused -- you can turn on the Optimize checkbox in the Bits per Pixel section to automatically delete unused colors.

• Load...

  This selection loads a palette from a standard GIF file and dithers the image to the palette. This could possibly leave some colors unused -- you can turn on the Optimize checkbox in the Bits per Pixel section to automatically delete unused colors. Loading a palette also adds the palette to the HVS ColorGIF preferences file. The names of stored palettes can later be chosen from the bottom of the list.

• Save

  This selection saves the current palette in a standard GIF file (without any image data) and adds it to the Palette popup menu for later use. The names of saved palettes can later be chosen from the bottom of the list.

• Delete

  This selection allows you to delete a user palette from the menu.