SPOT 4.1 Basic and Advanced Software Manual for SPOT Insight ...

Ch. 8 – Viewing, Editing, and Annotating ImagesFilter NoiseThe Noise Filter corrects for the effects of electrical or thermal noise. When capturing dim images withlengthy exposure times, the noise filter acts as a “virtual cooler” for the Insight camera, eliminating “hotpixels.” The Noise Filter checks each pixel on the CCD chip as described below:1. The program compares the value of each red pixel with the values of the eight neighboring red pixels.2. If none of the eight neighboring red pixels has a value within ± X % (X being the threshold value thatthe SPOT user specifies) of the value for the red pixel being checked, the value for the red pixel beingchecked is replaced with the average value of the eight neighboring red pixels.3. The program repeats this procedure for the values of the green and blue pixels being checked.To filter noise, follow these steps:1. From the Edit menu, select Filter > Filter Noise.2. Enter a value between 10% and 100%. The Threshold value is setto a default of 50%, but will default to the last used settingthereafter. Refer to the procedure described at the start of the FilterNoise section for an explanation of the Threshold value.3. Click on OK. The filtered image appears on-screen.Note: Image setups can be defined to automatically use the noise filter when capturing animage. Refer to Ch. 5 – Preparing to Take a Picture for details.Median FilterThe Median Filter corrects for the effects of shot noise. This filter functions by considering a sample pixeland its surrounding 8 pixels. The values of all nine pixels are compared and the median value of the groupis substituted for the sample pixel. In this process, all pixels are always being modified, unless, of course,the sample pixel is the median value of the group.Unlike the Filter Noise function, there is no need for any user inputs regarding the median filter process.This approach negates any impact that a hot pixel might have on the filtered value of another neighboring(sample) hot pixel.Note: Filtering algorithms always utilize original data for each sample pixel being considered.In other words, filtered (substituted) pixel data is not used in the filtering process.Make NegativeMake Negative to make a color negative (with complimentary colors) of an image. From the Edit menu,select Make Negative. The Program automatically converts the image to a negative.Convert to Gray ScaleUse Convert Gray Scale to convert images from color to gray scale. The Convert to Gray Scale optionworks only with color (24 bit and 36 bit) images.154 User Guide to the SPOT Insight Camera