Focus automatically assigns red, green, and blue (RGB) values to the first three channels. You can assign color channels to define the reference image that will be used during training site data collection and in any subsequent post-classification analysis.
Because supervised classification requires you to rely on your own pattern-recognition skills and a prior knowledge of the scene, you may need to visually identify your training areas from familiar colors in the ground cover. In such cases, you must change the RGB values to match the TM bands in the image data to produce a true color-reference image.
The task of collecting training areas is made easier by working with a reference image that simulates normal or true color. However, personal preferences often guide the choice of band - color combinations for interpretive purposes. In some applications, you must use a different combination of color channels; for example, channels that fall outside the visible color range.
Whatever your preference, it is unlikely that the default color assignment offered in the Session Configuration window will coincide with your choice. You can reset the color assignments by clicking the corresponding cell of the desired channel in each of the Red, Green, and Blue columns. You can rearrange the color channels to see a true color rendition of the image in the view pane.
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