PNG: a non lossy format allowing for both full color and paletted. On the contrary, it’s not suited to most vector layers, because even slight compression generates visible artifacts on uniform color areas. JPEG is best suited for imagery layers, where the pixel color varies continuously from one pixel to the next one, and allows for the best compressed outputs. JPEG: a lossy format with tunable compression. Internet standards offer a variety of image formats, all having different strong and weak points. In the latter case, the smaller footprint of paletted images is usually a big gain in both performance and costs, because more data can be served with the same internet connection, and the clients will obtain responses faster. For many maps, one can easily find 256 representative colors. Depending of the actual map, this may be a very stringent limitation, visibly degrading the image quality, or it may be that the output cannot be differentiated from a full color image. This allows for images that are 3-4 times smaller than the standard images, with the limitation that only 256 different colors can appear on the image itself. Basically, instead of representing each pixel with its full color triplet, which takes 24bits (plus eventual 8 more for transparency), they use a 8 bit index that represent the position inside the palette, and thus the color. Some image formats, such as GIF or PNG, can use a palette, which is a table of (usually) 256 colors to allow for better compression. This tutorial introduces you to the palette concepts, the various image generation options, and offers a quality/resource comparison of them in different situations. GeoServer has the ability to output high quality 256 color images.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |