Specifying publish settings for PNG files

PNG is the only cross-platform bitmap format that supports transparency (an alpha channel). It is also the native file format for Macromedia Fireworks.

Flash exports the first frame in the SWF file as a PNG file, unless you mark a different keyframe for export by entering the frame label #Static.

To publish a PNG file with your Flash SWF file:

Do one of the following to open the Publish Settings dialog box:
- Select File > Publish Settings.
- In the Property inspector for the document (which is available when no object is selected), click the Settings button.
Note: To create a publish profile for the publish settings that you'll specify, see Using publish profiles.
On the Formats tab, select the PNG Image type. For the PNG filename, either use the default filename, or enter a new filename with the .png extension.
Click the PNG tab. For Dimensions, enter values for width and height in pixels for the exported bitmap image, or select Match Movie to make the PNG image the same size as the Flash SWF file and maintain the aspect ratio of your original image.
Select a bit depth to set the number of bits per pixel and colors to use in creating the image:
- Select 8-bit for a 256-color image.
- Select 24-bit for thousands of colors.
- Select 24-bit with Alpha for thousands of colors with transparency (32 bits).
The higher the bit depth, the larger the file.
Select options to specify appearance settings for the exported PNG:
Optimize Colors removes any unused colors from a PNG file's color table. This option reduces the file size by 1000 to 1500 bytes without affecting image quality but increases the memory requirements slightly. This option has no effect on an adaptive palette.

Interlace incrementally displays the exported PNG in a browser as it downloads. Interlacing lets the user see basic graphic content before the file has completely downloaded and may download the file faster over a slow network connection. Do not interlace an animated PNG file.

Smooth applies anti-aliasing to an exported bitmap to produce a higher-quality bitmap image and improve text display quality. However, smoothing may cause a halo of gray pixels to appear around an anti-aliased image placed on a colored background, and it increases the PNG file size. Export an image without smoothing if a halo appears or if you're placing a PNG transparency on a multicolored background.

Dither Solids applies dithering to solid colors and gradients. See Dither options in step 6.

Remove Gradients, turned off by default, converts all gradient fills in the application to solid colors using the first color in the gradient. Gradients increase the size of a PNG and often are of poor quality. If you use this option, select the first color of your gradients carefully to prevent unexpected results.
If you chose 8-bit for Bit Depth in step 4, select a Dither option to specify how pixels of available colors are mixed to simulate colors not available in the current palette. Dithering can improve color quality, but it increases file size. Select from the following options:
None turns off dithering and replaces colors not in the basic color table with the solid color from the table that most closely approximates the specified color. Turning dithering off can produce smaller files but unsatisfactory colors.

Ordered provides good-quality dithering with the smallest increase in file size.

Diffusion provides the best-quality dithering but increases file size and processing time. It also works only with the web 216 color palette selected.
Select Palette Type to define the color palette for the PNG image:
Web 216 uses the standard 216-color, browser-safe palette to create the PNG image, for good image quality and the fastest processing on the server.

Adaptive analyzes the colors in the image and creates a unique color table for the selected PNG file. This option is best for systems displaying thousands or millions of colors; it creates the most accurate color for the image but results in a file size larger than a PNG created with the web 216 palette.

Web Snap Adaptive is the same as the Adaptive palette option except that it converts very similar colors to the web 216 color palette. The resulting color palette is optimized for the image, but when possible, Flash uses colors from web 216. This produces better colors for the image when the web 216 palette is active on a 256-color system.

To reduce the size of a PNG file with an adaptive palette, use the Max Colors option to decrease the number of palette colors, as described in the next step.

Custom specifies a palette that you have optimized for the selected image. The custom palette is processed at the same speed as the web 216 palette. To use this option, you should know how to create and use custom palettes. To select a custom palette, click the Ellipsis (...) button to the right of the Palette box at the bottom of the dialog box and select a palette file. Flash supports palettes saved in the ACT format, exported by Macromedia Fireworks and other leading graphics applications; for more information, see Importing and exporting color palettes.
If you selected the Adaptive or Web Snap Adaptive palette in step 7, enter a value for Max Colors to set the number of colors used in the PNG image. Choosing a smaller number of colors can produce a smaller file but may degrade the colors in the image.
Select Filter Options to select a line-by-line filtering method to make the PNG file more compressible, and experiment with the different options for a particular image:
None turns off filtering.

Sub transmits the difference between each byte and the value of the corresponding byte of the prior pixel.

Up transmits the difference between each byte and the value of the corresponding byte of the pixel immediately above.

Average uses the average of the two neighboring pixels (left and above) to predict the value of a pixel.

Path computes a simple linear function of the three neighboring pixels (left, above, upper left), and then chooses as a predictor the neighboring pixel closest to the computed value.

Adaptive analyzes the colors in the image and creates a unique color table for the selected PNG file. This option is best for systems displaying thousands or millions of colors; it creates the most accurate color for the image but results in a file size larger than a PNG created with the web 216 palette. You can reduce the size of a PNG created with an adaptive palette by decreasing the number of colors in the palette.
To save the settings with the current file, click OK.