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R G B Overlay


Normally, the RGB overlay is used to show three x-ray maps (or the like) at once. For this demo, I split an ordinary color photograph into the red, green and blue channels, which can be recombined using the RGB overlay feature.

Color overlay Demo (also see Superconducting precursor demo)
Once the windows (images) are displayed , they may be picked for an RGB overlay using the X/Red Image..., Y/Green Image..., and Z/Blue Image... buttons, just at they are picked for scatter diagrams. Here, the red image has been selected, and the green image is being selected with a pop up menu. select green image button

After picking a red, green and blue window, use this button to make a color overlay of the three. The name of the overlay is a combination of its three components. Here is an expanded view of the top of the color overlay showing the full title bar:

Here are three different versions of the same overlay image, displayed with different settings of the monitors control panel.



256 Colors
The thousands and millions of color settings for the monitor look allright. The 256 colors image looks blotchy because MacLispix uses the system palette for displaying color overlays, when the monitor is set for 256 colors. More about colors.

The image is displayed in 24 bit color, but if you are using a monitor setting of 256 colors, I will look as if I have some strange skin disease. The Kowala looks OK for the most part. The reason for the 'blotchies' is the way the system maps the many colors of the overlay into the 256 colors of the system palette.

It is tricky to display color images of this sort so that they look good with 256 colors. Adobe photoshop is one program that does do this. To display the overlay using Adobe, save the overlay with the {MLx - image windows - save as tiff - 24 bit color} menu. It will be saved as a tiff file. The overlay window has a long name that must not be used for the file - hold down the shift key while choosing the folder in which to store the file so that you can type in a more suitable name. Open the file with Adobe, and it will look close to the way MacLispix would display the image with millions of colors. In the unlikely event that a color monitor is not available, the overlay should look reasonable as a gray level image:

The window can be saved as an RGB TIFF file, that has 24 bits of color information, regardless of the settings of the computer monitor.

The overlay is made from the scaled image arrays associated with the three windows. This means that the intensity of the red, green or blue color (gun) will be the same as the intensity of the image as it is displayed in the gray scale window. Any scaling done to the window will be reflected in the color overlay.

The overlay looks best if displayed with thousands or millions of colors. Approximate colors are used if 256 colors is selected (in the Monitors control panel), and even more approximate colors are used if 16 colors is selected. Approximate colors tend to give a blotchy appearance to the image - see the RGB overlay demo for an example of this.

gray level version of the color overlay