That is, the 8-bit intensity for each element in the image array is an index that points to an entry in the color table. PseudoColor images are displayed using the Indexed color model described in Chapter 5. The scaling may be done automatically by IDL, or it may be done manually. If the native data type of the image is not byte, scaling to byte type is required to display the image. PseudoColor image arrays may be of any numeric data type however, only 8-bit byte representations may be displayed. PseudoColor images are two-dimensional arrays with dimensions of the form where nx is the number of columns and ny is the number of rows. The purpose of this chapter is to describe how images of different types may be displayed on IDL graphics devices, taking into account any differences between the abstract representation of the image in memory and the physical characteristics of the display device. However, it is important to realize that regardless of the display mode, color model, or graphics device used by IDL, an image is simply a representation of a two-dimensional scene that takes the form of an array in memory. There is necessarily some overlap between the description of image types in this chapter and the description of display modes and color models in Chapter 5. IDL is equally adept at displaying each image type, regardless of the output graphics device. TrueColor images combine red, green, and blue intensities for each image pixel to determine the color displayed. PseudoColor images are associated with a color table that defines the color displayed for each image pixel. There are two basic types of images that may be displayed in IDL: Pseudo-Color and TrueColor. GUMLEY, in Practical IDL Programming, 2002 7.1 IMAGE FUNDAMENTALS
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