MrSID
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| MrSID | |
|---|---|
| File name extension | .sid |
| Internet media type | image/x-mrsid, image/x.mrsid, image/x-mrsid-image |
| Developed by | LizardTech |
| Type of format | lossless or lossy bitmap image format |
MrSID (pronounced Mister Sid) is an acronym that stands for multiresolution seamless image database. It is a file format (filename extension *.sid) developed and patented by LizardTech for encoding of georeferenced raster graphics, such as orthophotos.
Contents |
[edit] Common uses
[edit] Geographic information systems
MrSID was developed primarily for Geographic Information Systems (GIS). With this format, massive image data can be partitioned and displayed as satellite imagery in map software.
[edit] World-wide web
Since MrSID files contain multiple scale and quality levels they are claimed to be well suited for streaming over the World Wide Web. Only the requested zoom and area of the image is sent to the browser. Since the format is not well supported among most image programs, the resulting images cannot be usefully saved. Additionally, the browser plugin is slow when attempting to zoom or pan through a picture.
[edit] Software
LizardTech offers a software package called GeoExpress to read and write MrSID files. They also provide a free web browser plug-in. Most commercial GIS software packages can read MrSID files including those from GE Smallworld, ESRI, Intergraph, Bentley Systems, MapInfo, Safe Software, Autodesk and ERDAS.
There is no Open Source implementation of the MrSID format. Some Open Source GIS systems can read MrSID files, including MapWindow GIS and those based on GDAL. However, this requires linking to the proprietary Lizardtech libraries.
Some image editing and management software systems can also read MrSID files; Xnview, IrfanView
[edit] Technology
[edit] Encoding
MrSID technology uses lossless wavelet compression to create an initial image. Then the encoder divides the image into zoom levels, subbands, subblocks and bitplanes. After the initial encoding, the image creator can apply zero or more optimizations. While 2:1 compression ratios may be achieved losslessly, higher compression rates are lossy much like JPEG-compressed data.
[edit] Decoding
MrSID uses selective decoding meaning that the decoder does not have to decode the entire file to view a specific zoom level, image quality or scene for example.
