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Color Depth
| Product: | SnagIt |
| Platform: | Win 98 and above |
| Version: | 7 and above |
The Color Depth options allow you to customize the color depth, dithering, and palette features of an image capture. If you want your files to be as small as possible so that they download faster when you share them on your Web site, or if you want to save an image as a GIF, this usually means you want to reduce the color depth of your image captures to 256 colors or less. You can use the Custom Color Depth options in SnagIt to do this.
When you set the Custom Color Depth to 256 colors or less (24-bit), the Dithering and Palette options become enabled. To give you the best results, SnagIt defaults to No Dithering and an Identity Palette. But if you want to change the dithering and palette settings, you can do that.
Dithering Options
Dithering makes an image look a little smoother, which can be helpful when an image's Color Depth is reduced. If dithering is not used, the resulting image may look blotchy if it contains very subtle color variations. Dithering emulates the image's original color by mixing-in pixels of different colors. These seemingly random pinpoints of different color are not likely to be discerned when viewed at original size, but are easily seen when zoomed. In the end, the choice of a dithering method depends greatly on the results you seek, and you should try various methods when you need to achieve a specific result. You can always undo any attempts that don't work well.
Color Palette Options
A palette is an array that contains the colors for displaying an image. The pixel values are indexes into the array. An image can have its own unique palette or it can share a common fixed palette. In either case, every bitmap in memory that is 8 bits per pixel (256 colors) or less has its own copy of a palette (even if it is a common fixed palette).
Use and Change the Custom Color Depth Options
Note: The Color Depth option is used to set an image's color depth either during capture or during post-capture processing.
Choose Filters > Color Depth > Custom Color Depth and the Color Depth dialog box opens. This dialog box can also accessed from the Preview Window or SnagIt Editor by choosing Colors > Color Depth.
Make your seelctions and then choose OK to accept all changes. If you are using the Preview Window or SnagIt Editor, you see the results of your changes on the full-size, captured image. If you don't like them, select Edit > Undo or press <CTRL + Z>. There is no limit to the number of times you can undo.
Note: You get the best possible image quality by using a unique, Optimized palette. To make sure a bitmap has a unique palette, open an image from a file that is 8 bits per pixel (256 colors) or fewer. This file contains a unique palette for the image. By default, SnagIt loads the palette that is stored in the file and relates it to the bitmap in memory. Or let SnagIt make an optimized palette for the image by decreasing a 24-bit image (16 million colors) to 8 bits per pixel (256 colors). Images with optimized palettes may exhibit some palette shift.
The following table summarizes the description and use of each option in the Color Depth dialog box.
| Option |
Description & Use |
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Colors
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Choose the desired image resolution from the Colors list box. The options available range from Monochrome (1-bit) to True Color (32-bit).
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Color Order
(This option is only available with 16-bit or higher color, and only from the Preview Window or Editor)
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This option allows you to specify the Color Order: Red-Green-Blue or Blue-Green-Red.
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Dither Method
(This option will be available only if Colors is set to 256 or fewer colors.)
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Use the Dither Method list box options to make the image look smoother when an image's color resolution is decreased. The Dither Method list box offers the following options:
None. No dithering will be used.
Ordered dithering is the fastest method. This is effective for reductions to 256 colors or less. It places pixels from shades next to the original color in the mix to achieve a smoothing effect. Since most palettes are ordered so that similar shades of color are next to each other. Pixels used in dithering are taken from these adjacent colors to achieve the nearest shade. All of the other dithering methods in SnagIt use error-diffusion algorithms. In error diffusion, the error is the difference between the original pixel color and the nearest match, and the algorithm performs diffusion (spreading of pixel placement) of this error.
Floyd-Steinberg is a high-quality, fast error-diffusion method. It is the default method that SnagIt uses to dither during color depth reduction. All of the other methods are slower than Floyd-Steinberg, and the quality may or may not be better. The results depend on a lot of factors, including the nature of the original and the intended use of the reduced image.
Stevenson Arce dithering is the slowest method, but it is most likely to produce higher-quality images.
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Palette
(This option will be available only if Colors is set to 256 or fewer colors.)
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Four Palette options are available:
Fixed saves the image using a common Fixed palette. The advantage to using a fixed palette is that it avoids palette shift. Palette shift occurs when a display device uses only one palette at a time to display colors. Therefore, if you are displaying more than one image at the same time, the current image may look perfect, while all of the others look bad, because they are mapped to the wrong palette. Using a fixed palette solves the potential palette shift problem.
Optimized saves the image using a palette optimized for this image. For example, if you reduce a 24-bit image (16 million colors) to 8 bits per pixel (256 colors), you can let SnagIt create an optimized palette for the image. This choice is guaranteed to look the best for a single image displayed on the screen by itself. However, when displaying multiple images on the screen at once, each with its own different optimized palette, none of the images may look good. In general, you should use an Optimized palette if the image will be viewed by itself.
Identity saves the image using the Windows system palette. Use this choice if the image uses common Windows screen colors (for example, a screen shot of Windows Explorer or some other Microsoft-developed software).
Netscape (only available when Colors is set to 256 colors) saves the image using the palette used by Netscape Navigator and Microsoft Internet Explorer. Use this choice for multiple images that need to be viewed on the screen at the same time. The Netscape palette is preferred for images published on a Web page.
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OK
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Choose OK to save changes and exit this dialog box.
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Cancel
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Choose Cancel to exit this dialog box without saving changes.
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Default
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Choose Default to restore the options back to their original settings.
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Help
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Choose Help to access the online help system.
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