PNG Save Options

 

These options determine how PMView saves PNG files.

 

Use Adam7 interlacing If set, the image will be saved using Adam7 interlacing (7-pass). If not set, the image will be saved sequentially in one pass. Using interlacing only makes sense with programs that progressively update the display while loading. For instance, when loading an interlaced PNG file the image resolution will gradually increase during seven passes. Interlacing slightly expands the file size on average, but it gives the user a meaningful display much more rapidly. Interlacing is for instance useful when transferring images over slow transmission lines (eg. modems). However, note that it is generally not a good idea to use interlacing unless you need it, since it may slow down normal loading from disk by several magnitudes due to the overhead caused by multiple painting passes.

 

Write histogram chunk If set, a histogram chunk [hIST] will be written to the PNG file. The histogram chunk gives the usage frequency of each color in the palette. If a viewer is unable to provide all the colors listed in the palette, the histogram may help it decide how to choose a subset of the colors for display. You may need this option if you know that the target application can make use of the hIST chunk if present. PMView will not use this chunk (PMView builds its own histogram during loading).

 

Write time chunk If set, a last modification time chunk [tIME] will be written to the PNG file. Note that the written time is local time.

 

Write transparency chunk If set, a transparency chunk [tRNS] will be written to the PNG file. Use this option if you would like one of the colors in your image to be transparent with the background. Typically you'll need this if you make images for WWW-browsers. Note that viewers are not bound to honor this information. PMView does not use this information when loading PNG files.

 

Write background chunk If set, a background chunk [bKGD] will be written to the PNG file. Use this option if you would like to specify a suggested background color. Typically may need this if you make images for WWW-browsers. Note that viewers are not bound to honor this information a viewer may choose to use a different background color. PMView does not use this information when loading PNG files.

 

Transparency - Colormapped images The index of the palette entry that is to be treated as transparent for Colormapped images. For Grayscale images this is the gray level of the pixels that are to be treated as transparent.

 

Transparency - RGB images The RGB color value of the pixels that are to be treated as transparent for RGB deep color images.

 

Background - Colormapped images The index of the palette entry that is to be used as background color for Colormapped images. For Grayscale images this is the gray level that is to be used as background color.

 

Background - RGB images The RGB color value of the color that is to be used as background color.

 

Related information:

The Portable Network Graphics Format