Images

Images

WORLD FILE

Dx (usually positive Cell Width)
Horizontal Skew (usually 0)
Vertical Skew ( usually 0)
Dy (usually negative Cell Height)
X of Top Left Corner Cell Center
Y of Top Left Corner Cell Center

 

Images represent everything from a standard RGB image like we conventionally use with computers to multi-layered hyperspectral images that must have certain bands selected before it can be constructed into a representation on the screen.  Small images are usually stored in png, jpg, bmp, gif, tif or other common image formats.  However for really large images, it becomes more and more advantageous to use a better compression algorithm.  These algorithms are not commonly used yet, but offer better compression ratios and allow access to parts of the image faster than would be true for a conventional image compression method.  The most popular extensions for this type of wavelet compression include jp2, ecw and sid.  Some image formats like geotiff include georeferencing information that is necessary to draw the image in the correct location on the map in tags within the image itself.  Most images, however, provide that information in an external “world” file which consists of 6 values listed on separate rows making up the affine transform coefficients.  Word files usually have the first and last letter of the image format extension followed by a w.  For instance jpg becomes jpw.  The values are listed as follows:

The Basic data structure for working with images is the “InRamImageData” object.  This is easy to use and provides all the basic capabilities of the .Net Image class but with the benefit of an added WorldFile.  Expert classes include a PyramidImage, which can work with large file-based images, but is an internal format only, and not a public standard, as well as the GdalImage, which requires the use of the GDAL image libraries, which are compiled for x86.

Beginner

expert

Last edited Nov 9, 2010 at 7:07 AM by Shade1974, version 2