PNG is the only cross-platform bitmap format that supports transparency (alpha channel). It is also the native file format for Macromedia Fireworks.
Flash exports the first frame in the movie as a PNG, unless you mark a different keyframe for export by entering the frame label #Static.
Use the controls in the PNG panel of the Publish Settings dialog box to change the following settings:
Dimensions Sets the size of the exported bitmap image to the number of pixels you enter in the Width and Height fields. If you turn on Match Movie, the entries in the Width and Height fields have no effect and Flash makes the PNG the same size as the movie. Flash ensures that the size you specify always has the same aspect ratio as your original image.
Bit Depth Specifies the number of bits per pixel to use in creating the image. The bit depth determines the number of colors to be used in the image. For a 256-color image, choose 8-bit; for thousands of colors, choose 24-bit; for thousands of colors with transparency (32 bits) choose 24-bit with Alpha. The higher the bit depth, the larger the file.
Options Specify a range of appearance settings for the exported PNG.
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Optimize Colors removes any unused colors from the color table of a PNG file. This can reduce the size of a PNG file by 1000-1500 bytes with no sacrifice in image quality. It does, however, cause a small increase in the memory requirements and processing required on the server. Note that this option has no effect with an adaptive palette. |
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Smooth enables or disables anti-aliasing in the exported bitmap. Smoothing produces a higher quality bitmapped image. Text display quality is poor without anti-aliasing. However, a halo of gray pixels may appear around an image placed on a colored background. Export without smoothing if a halo appears, or if you are creating a transparent PNG that will be placed over a multicolored background. Turning this option off makes PNG files smaller. |
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Interlace makes the exported PNG display in a browser incrementally as it downloads. An interlaced PNG provides the user with basic graphic content before the file has completely downloaded and may download faster over a slow network connection. |
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Dither Solids applies dithering to solid colors as well as gradients and images. see the definition of dithering that follows. |
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Transparent displays a transparent PNG. A transparent PNG allows the background of your web browser to show through the portions of the PNG where you have not drawn any images. If you create a transparent PNG, set the background color by choosing Modify > Movie to match the web page background. Use the Smooth options to further optimize the color match. |
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Remove Gradients converts all gradient fills in the movie to solid colors using the first color in the gradient. Gradients increase the size of a PNG and often are of poor quality. When using this option you must choose the first color of your gradients carefully to prevent unexpected results. The default is false. |
Dither Enables or disables dithering and specifies the method. Dithering displays pixels of a range of similar colors to simulate colors not available in the current palette. With dithering off, Flash replaces colors not in the basic color table with the solid color from the table that most closely approximates the specified color; not dithering can produce smaller files, but check the results to see if the colors are satisfactory. Dithering can help if a transparent image contains artifacts. Dithering increases the files size. Choose from the following dithering options:
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None disables dithering. |
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Ordered provides good quality dithering with the least possible file size increase. |
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Diffusion provides the best quality dithering but increases file size more than Ordered dithering. It also only works with the Web 216 color palette selected. |
Palette Type Defines the color palette to use for the image. Choose from the following options:
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Web 216 uses the standard 216-color browser-safe color palette to create the PNG image. This provides good image quality and the fewest color problems in all types of browsers. |
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Adaptive analyzes the colors in the image and creates a unique color table for the particular PNG. This creates the most accurate color for the image but the resulting file size is 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 (see the Max Colors option that follows). An adaptive palette works best for systems displaying thousands or millions of colors. |
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Web Snap Adaptive is the same as the Adaptive palette option except that it "snaps" close 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. |
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Custom lets you specify a palette that you have optimized for the current image. To use this option you must be familiar with creating and using custom palettes. To choose a custom palette, click "..." 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. This is the same format exported by Macromedia Fireworks and other leading graphics applications. |
Max Colors Sets 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. You can specify a value for the maximum colors only when you have selected Adaptive or Web Snap as the Palette Type option.
Filter Options Specifies the filtering method for the PNG. Prior to compression, a PNG image is filtered line-by-line to make it more compressible. Compare the results of the different options to see which works best for a particular image. The choices are the standard PNG filtering options:
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None provides no filtering. |
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Sub transmits the difference between each byte and the value of the corresponding byte of the prior pixel. |
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Up transmits the difference between each byte and the value of the corresponding byte of the pixel immediately above. |
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Average uses the average of the two neighboring pixels (left and above) to predict the value of a pixel. |
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Paeth computes a simple linear function of the three neighboring pixels (left, above, upper left), then chooses as predictor the neighboring pixel closest to the computed value. |