Figure 13.2 This is a histogram of the image of M101 in Figure 13.1. Although pixel values in this 12-bit image range from 0 to 4095 ADUs, 99% of them are below 1100, and 99.9% of the pixels have values below 2100. This is why, on a 0-to-4095 scale of pixel value, the image appears so dark.

ing, you specify the desired shape of the new histogram—usually one known to produce good-looking images reliably—and tell the software to generate a transfer function matched to the original image, and then convert pixel values to a new image that will have the histogram you specified.

In the following sections, we explore a variety of transfer functions and how the different methods of endpoint specification operate.

• Tip: In AIP4Win, you'll find point operations in the Enhance menu under Pixel Math, Pixel Ops, Brightness Scaling and Histogram Shaping. Pixel Math is a tool for direct specification. Pixel Ops gives you access to pre-programmed transfer functions. Brightness Scaling is a powerful tool that supports both direct and histogram endpoint specification with a handy preview function. The Histogram Shaping tool gives you easy access to a variety of histogram profiles, each with previewing.

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