IHS is an easier means of controlling the output color than RGB. For example, it is easier to comprehend lightening an image (increasing the intensity) or adding more color (increasing the saturation) than it is to comprehend the effects of increasing or decreasing the RGB values. One possible application of IHS is to produce channels from three input channels, stretch the saturation channel, and then convert the IHS channel data back to the equivalent RGB channels for video display. The output image would have a better saturation range without changing the colors of the original image.
The following diagram shows the geometric relationship between the RGB and IHS coordinate systems for representing color. The hexcone or cylinder is oriented so that the angles between the Intensity axis and the primary RGB color axes are the same. The Saturation axis is perpendicular to the Intensity axis. Hue is the angle between the radius of the circle defined by the RGB value and the Saturation axis.
- With multispectral and panchromatic images open, open the Algorithm Library, and locate and double-click IHS.
- Select three image layers from your multispectral file for the red, green, and blue input layers.
- Click the Input Params 1 tab and choose a type of resampling you want to use from the Resample Mode list box.
- Click Run.
- Open the Algorithm Library, and locate and double-click RGB.
- Select a high-resolution panchromatic image layer as input for the intensity layer.
- Select hue and saturation outputs from IHS as the inputs for the hue and saturation input layers.
- Click the Input Params 1 tab and choose a type of resampling you want to use from the Resample Mode list box.
- Specify the output bit depth.
- Click Run.