Bitmap Export Dialog Box - Palette Options

Dithering

Dimmed for True Color (PNG or BMP).

You can select between three types of dithering with these options. Choosing None means there will be no dithering, Ordered using an ordered (regular) dithering pattern and Error diffusion uses error-diffused dithering (a more complex dithering technique). In general, error diffusion will give the best results, but only use dithering when really necessary as it prevents the file compression working so well and so makes files larger. You cannot use Ordered dithering with an optimized palette.

Note that you can set the dithering type for the screen display too, see Changing the screen dithering.

Palette

Dimmed for True Color (PNG or BMP).

Choose between browser palette, WebSnap palette and optimized palette

Color Depth

Choose the number of colors your bitmap requires. The more colors, the larger the bitmap file. (Except PNG format where True color may give smaller files than 256 colors).

Transparent bitmaps with 256 colors or less use one of the colors for the transparency. This means a 2 color transparent bitmap has one color plus transparency.

Max colors

Dimmed for BMP format and PNG True Color.

With this field, you can specify how many colors in the palette of the bitmap are actually used. This means you can create, for example, an 256 color bitmap where only 100 of the 256 palette entries are used. The least used colors are discarded first. This can mean that distinctive colors are discarded (for example a small area of red in a largely blue graphic). If this happens, you can restore the color to the palette using Restore.

With some experimentation you can alter this setting to create bitmaps that are very small by reducing the number of colors until the quality is just at the level you will accept.

Palette colors

GIF, PNG & BMP (up to 256 colors only)

This displays the range of colors in the current palette. Click on a color to select it.

You can edit any of the colors if you want extra control - see Editing colors in the export palette.

To check where colors are used in the bitmap, select the Color Selector button (between the two previews). Then, as you move over the image in the Preview window, the color under the pointer is highlighted in the palette.

Small squares on the colors give you extra information about the color.

Buttons

Dimmed for True Color (PNG or BMP).

These buttons (except Transparent background) apply to the selected color: click on a color in the palette (above the buttons) to select it. You can also select these options by right-clicking on a color, then selecting from the pop-up menu.

(Lock): always include this color in the palette. This is useful if you are reducing the number of colors in the palette. For more information see Locking a color.

(Web-safe): snap this color to the nearest color in the 216-color Netscape Navigator and Microsoft Internet Explorer palette. This means the color isn't dithered on 256-color displays and so looks better. For more information see Making a color web-safe.

(Transparent background): dimmed for BMP format and PNG True Color. Make transparent any areas not covered by the selected objects. Selecting this option automatically makes one entry in the palette transparent. Transparent on the Options tab duplicates this button.

(Transparent): make this color entry transparent. GIF and PNG (256-colors or fewer) can have simple on-off transparency by making entries in the palette transparent. Note the difference between this option which makes parts of the selected objects transparent and Transparent background which makes transparent those areas behind the selected objects. For more information see Making a color transparent.

(Delete): delete this color from the palette. Any areas in the bitmap that use the deleted color then use the nearest color in the palette. The fewer colors in the palette the smaller the bitmap file. Click R to undo a delete. For more information see Deleting a color.

(Restore): undelete this color.

(Add system colors): dimmed for BMP format and PNG True Color. Adds 28 colors to the palette. These colors are the regular Windows system colors and a number of primary colors. This ensures the palette includes a spread of colors and may improve the quality of the image, particularly if it contains a wide range of colors. You may need to experiment with this option to get the best results.

Sort By:

Controls the order in which colors are displayed in the palette. This option applies only to the display in this dialog box. It has no effect on the exported bitmap nor on the actual colors. Options:

Number of uses - arranged by the area each color covers.

Luminance - arranged by the RGB brightness of the colors.

Hue - arranged by hue.