Some images may contain patterns in visual brightness that could affect the seamless integration of the images into a mosaic. CATALYST Enterprise provides various normalization methods you can use to even out the bright and dark effects to achieve a more pleasing mosaic. Normalization is not intended to remove distinct cloud shadows but, under most circumstances, a small amount of nonuniformity always exists in airphotos due to variations in the intensity of haze or the angle of the sun.
The available normalization methods are as follows:
- The Hot Spot method removes hot spots by fitting a Gaussian surface to the brightness values. It is best suited for most aerial-photo applications in which the images were taken in uniformly overcast or sunny conditions.
- The Adaptive method is best suited to surfaces that do not exhibit variation in intensity that can be fit to a Gaussian surface. This can occur under circumstances of nonuniform haze. Use this method with caution, however, because overly aggressive filter parameters can "wash out" the natural variation in brightness and colors. It is recommended that the percentage value of the image filter for the Normalization Method Extra Options parameter be specified at 60 or greater.
The normalization method you select depends on the anticipated intensity variation of the data and can be dependent on flying conditions or acquisition method. In the following figure, A) is a Gaussian intensity variation, B) is nonuniform, and C) is linear.
With most aerial applications, the Hot Spot method provides the best overall result.