User Manual - pancroma

Another type of unwanted artifact is the “black spot” anomaly. In this case theimage suffers from black blobs seemingly randomly scattered across the image.For example, if the SPOT image in the Video 7 tutorial listed on thewww.PANCROMA.com website is pan sharpened with the default settings, theresult in the image below will be computed.This is an artifact of the algorithm for computing cumulative histograms for thepanchromatic and computed intensity images. The problem is unfortunately alsocommon when gap filling. It is sometimes associated with a lot of black pixels inthe image pairs.There are several remedies to this problem. The simplest is to disable histogrammatching. To do so check the 'Activate Image Processing Routines' checkbox on the main form before pan sharpening. When the image processing boxappears, click on the 'No Histogram Adjust' radio button. Then select'Process Image'. This will cause the image to be pan sharpened withouthistogram matching.Of course by disabling histogram matching you will forgo the benefits of theprocess. If you have a problematic image but still want to histogram match, thereare a few more possibilities. If you encounter the problem during gap filling, trychecking the ‘Activate Image Processing Routines’ check box at the bottom ofthe main window. When the Image Processing Data Input box becomes visible,check the ‘Enable Channel Level Adjust’ in the Input Channel Level AdjustGroup. Modify the grayscale intensity by adjusting the ‘gap adjustment level’slider bar. Often brightening the image a bit can address this problemsatisfactorily.61