Running the FUSE algorithm

Intensity/Hue/Saturation-FUSE performs data fusion of an input RGB color image on an input file with a black-and-white intensity image The result is an output RGB color image with the same resolution as the intensity image. If the input and output files are different, the input RGB color image is resampled using the specified resampling method. Either the Hexcone or Cylinder IHS color model is used for data fusion.

IHS converts red, green, and blue image channels to intensity, hue, and saturation image channels, which enhances and controls the output colors for a given set of input red/green/blue imagery.

CYLINDER was the original method used by the IHS and RGB programs in previous PCI Geomatics software releases (Version 6.0.1 and earlier). The Hexcone model is used by many commercial image processing software programs. One model can produce more visually pleasing results than the other, depending on the circumstances. The Hexcone model runs about 15% faster than the Cylinder model.

Running FUSE is similar to running IHS and RGB. IHS separates an RGB channel into three color space components (intensity, hue, and saturation) and places each in a separate channel. The RGB program can then be used to convert intensity, hue, and saturation channel output by IHS back to red, green, and blue channels. The IHS and RGB programs can enhance and control the output colors more easily for any three channels in an image database file.

In computer imaging, colors are produced as combinations of the additive primary colors (red, green, and blue). Another means of color definition is in terms of intensity, hue, and saturation.

Intensity is the lightness or darkness of a color. For example, in an axis that is equidistant from the three primary color axes, which are orthogonal or perpendicular to each other, zero intensity represents black. As the intensity is increased, the lightness increases and the darkness decreases. Full intensity (for 8-bit data, this is 255) represents white.

Hue refers to an actual color and is defined as an angle on a circle that is centered and perpendicular to the intensity axis. For the Hexcone model, zero degrees represents red and hue values cycle through Red-Green-Blue-Red; whereas, in the Cylinder model, zero degrees represents blue and hue values cycle in the opposite direction through Blue-Green-Red-Blue. The following table shows the unscaled and scaled hue values for both IHS models:

Table 1.
Hue Angle	Hexcone Unscaled	Model Scaled	Cylinder Unscaled	Model Scaled
Red	0	0	240	170
Yellow	60	42	180	128
Green	120	85	120	85
Cyan	180	127	60	42
Blue	240	170	0 or 360	0 or 255
Magenta	300	212	300	212
Red	360	255	240	170

Saturation is the amount of color present or the radius of the circle described by the hue. Zero saturation represents no color and would appear as a gray shade depending on the associated intensity; full saturation (1.0 for unscaled Hexcone model or 208.2066 for 8-bit unscaled Cylinder model) represents full color.

Full saturation accentuates the RGB components at the expense of other hues, in that other hues peak in their saturation at less than the maximum possible saturation.

With a multispectral and panchromatic images open, open the Algorithm Library, and locate and double-click FUSE.
Select the panchromatic image layer as input to the Intensity Layer.
Select the multispectral image layers as input into the Red, Green, and Blue image layers.
Click the Input Params 1 tab and choose a type of resampling you want to use from the Resample Mode list box.
Choose a model from the IHS Model list box.
Click Run.

An advantage of running IHS and RGB instead of only running FUSE is that you can enhance the output from IHS individually, and then use the enhanced output in RGB.