Image service GetTileImageInfo method
Gets information about the image format of the cache tiles.
A TileCacheInfo object that stores information about the location, scale levels, image tile size, and DPI for a cached image service.
Depending on how the cache for the image service was generated, five image formats may be available: PNG8, PNG24, PNG32, JPEG, MIXED. Compression quality only applies to lossy image formats (JPEG and MIXED).
- PNG8: A lossless, 8-bit color, image format that uses an indexed color palette and an alpha table. Each pixel stores a value (0-255) that is used to look up the color in the color-palette and the transparency in the alpha table. 8-bit PNGs are similar to GIF images and enjoy the best support for transparent backgrounds.
- PNG24: A lossless, three-channel image format that supports large color variations (16 million colors) and has limited support for transparency. Each pixel contains three 8-bit color channels and the file header contains the single color that represents the transparent background. Cached image tiles using PNG24 are significantly larger than those using PNG8 or JPEG.
- PNG32: A lossless, four-channel image format that supports large color variations (16 million colors) and transparency. Each pixel contains three 8-bit color channels and one 8-bit alpha channel that represents the level of transparency for each pixel. While the PNG32 format allows for partially transparent pixels in the range from 0 to 255, ArcGIS Server Image server caches only support fully transparent (0) or fully opaque (255) values in the transparency channel. Cached image tiles using PNG32 are significantly larger than the other ArcGIS Server cache image formats.
- JPEG: A lossy, three-channel image format that supports large color variations (16 million colors) but does not support transparency. Each pixel contains three 8-bit color channels. Caches using JPEG provide control over compression quality and can be more compact than the PNG format.
- MIXED: A combination of lossless and lossy formats. When a mixed cache is created, PNG 32 tiles are created anywhere that transparency is detected (in other words, anywhere that the data frame background is visible). The rest of the tiles are built using JPEG. This keeps the average file size down while providing you with a clean overlay on top of other caches. If you do not use the mixed mode cache in this scenario, you will see a nontransparent "collar" around the periphery of your image where it overlaps the other cache.