Image Processing - Other Features
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Image Processing
 What is an Image?
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     - Color Palettes
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Other Features

Iris contains many features in addition to the ones you have used already. Here are just a few more that you can try to see how they affect the image. You an always click the Undo button () if you do not like the change.

An important thing to remember about image processing is that there is no single "best" image you can produce. Some images show faint detail exceptionally well, but make the brightest areas of the image overexposed and washed out. If you are interested seeing in the brightest areas of the image, you are probably not going to be able to see the faint areas. The best image is the one that brings out the features in which you are most interested. Someone who is studying a different topic may find your image is not suited to their needs.

Color Palettes

When you load an image from a single filter, such as the green image, it is displayed as a grayscale. The brightest pixels are shown in white, dimmer pixels in shades of gray, and the dimmest areas are black.

Color palettes allow you to display pixels of different brightnesses with different colors. Sometimes color displays can bring out subtle details.

The color palette bar is in the Threshold window. You have three choices: grayscale, blue-yellow, or red-green-blue. You can also invert any of the color palettes with the button at the far right.

Exercise 8. Open an image using Iris (you may use an image you already have). Apply the different color palettes. Observe the changes. Invert all the palettes and observe the changes.

Question 4. What features stand out best using the grayscale palette? What features stand out best using blue-yellow? Using red-green-blue?

Log Scaling

A normal grayscale image uses linear scaling. If one pixel has twice as many counts as another, it is twice as bright. Linear scaling is not always the best choice, however. Logarithmic scaling may be more appropriate for some applications. Logarithmic scaling uses the logarithm of the number of counts in each pixel for the brightness. Logarithmic scaling means that if one pixel has ten times as many counts as another, it will appear twice as bright.

Exercise 9. Open an image. Click on the View menu and select Logarithm. Observe the changes. Repeat for a couple of different images (you may also need to adjust max and min brightness to get a good image).

Question 5. What features stand out when you use log scaling? What features are missing? For what types of objects do you think you should use log scaling?