Color Transforms

Use Color Transforms to convert three-band red, green, blue (RGB) images to one of several specific color spaces and from the selected color space back to RGB. Adjusting the contrast stretch between the two transforms, you can produce a color-enhanced color composite image.

Additionally, you can replace the value or lightness band with another band (usually of higher spatial resolution) to produce an image that merges the color characteristics of one image with the spatial characteristics of another image. ENVI does this automatically in HSV Sharpening.

The color spaces supported by ENVI include the hue, saturation, value (HSV), the hue, lightness, saturation (HLS) and the USGS Munsell.

The Munsell color system is used by soil scientists and geologists to characterize the color of soils and rocks. This color system has been modified by the U. S. Geological Survey to describe color in digital images. The transform converts RGB coordinates into the color coordinates Hue, Saturation, and Value (HSV). Hue ranges from 0-360, where 0 and 360 = blue, 120 = green, and 240 = red. Saturation ranges from 0 to 208 with higher numbers representing more pure colors. Value ranges from approximately 0 to 512 with higher numbers representing brighter colors.

Color transforms require three bands for input. These bands should be stretched byte data or selected from an open color display.

Reference

Kruse and Raines, A technique for enhancing digital color images by contrast stretching in Munsell color space, in Proceedings of the ERIM Third Thematic Conference, Environmental Research Institute of Michigan, Ann Arbor, MI, 1994: pp. 755-760.