Tips for choosing a cache image format

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I hvilket format skal verden gemmes i?
/Sik

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How do you store the world?

/Sik

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Below is a summary of the available image formats and their appropriate uses.

• PNG8 - Use this format for overlay services that need to have a transparent background, such as roads and boundaries. PNG 8 creates tiles of very small size on disk with no loss of information. However, you should use a different PNG format if your map contains more than 256 colors. Imagery, hillshades, gradient fills, transparency, and the antialiasing caching option can easily push your map over 256 colors.
• PNG24 - You can use this format for overlay services, such as roads and boundaries, that have more than 256 colors (if fewer than 256 colors, use PNG 8). Do not use PNG 24 if your tiles will be viewed in Internet Explorer version 6 or previous.
• PNG32 - Use this format for overlay services, such as roads and boundaries, that have more than 256 colors. This format creates larger tiles than PNG 24, but the tiles are fully supported in all browsers.

• JPEG - Use this format for base map services that have large color variation and do not need to have a transparent background. For example, raster imagery tends to work well with JPEG.

  JPEG is a lossy image format. It attempts to selectively remove data without affecting the appearance of the image. This can cause very small tile sizes on disk, but if your map contains vector linework or labels, it may produce too much "noise" or blurry area around the lines. If this is the case, you can attempt to raise the Compression value from the default of 75. A higher value such as 90 may balance an acceptable quality of linework with the small tile size benefit of the JPEG.

  It's up to you to decide what image quality you consider acceptable. If you are willing to accept a minor amount of noise in the images, you may save large amounts of disk space by choosing JPEG. The smaller tile size also means the browser can download the tiles faster.

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Read more: http://blogs.esri.com/Dev/blogs/arcgisserver/archive/2008/10/17/Tips-for-choosing-a-cache-image-format.aspx

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