color stretch menu

Color images actually consist of three black & white images: a Red image, Green image, and a Blue image. The system determines which color to display for a pixel by looking at the red, green, and blue intensity levels for that pixel.

Stretching a color image is similar to stretching a black & white image, only you specify a mapping function for each of the three component images. If you are unfamiliar with the black & white stretching procedure, it would probably be a good idea to try that out before you try stretching a color image.

When you first enter this menu, all three mapping functions are initialized to the straight-line state. If you click on the DISPLAY COLOR IMAGE menu field a this point, you will see the color image in its original form. To modify the color balance, click on the DISPLAY RED HISTOGRAM, DISPLAY GREEN HISTOGRAM, or DISPLAY BLUE HISTOGRAM menu field, and alter the mapping function the same way you do in the black & white stretch menu. You can then either display the color image, or just the single component image to see the effect of your modification. When you are satisfied with the image, be sure to click on the STRETCH menu field to apply the stretch to the image.

As with the black & white stretch menu, you can equalize a component histogram, or you can make the system equalize all three histograms at once by clicking on the EQUALIZE THREE HISTOGRAMS menu field. Everything else in the menu functions in the same way as the black & white stretch menu.

You can see where particular image pixels fall in a histogram by moving the mouse to the portion of the image you are interested in, and clicking on button 2. The system will put a small arrow on the currently displayed histogram to indicate the intensity of that pixel. This is called backpicking.

You can restrict the stretch to work on only a portion of the image by specifying an Area of Interest (AOI). To specify a rectangular AOI, first display the image, then click on USE RECTANGULAR AREA. The system will prompt you to indicate the rectangular area on the image. Do so with two clicks. When you then apply the filter, only the pixels in the rectangular area will be affected. If you have restricted processing to an AOI and you want to make it apply to the entire image again, click on USE ENTIRE IMAGE.