Processing Raw Images

The VOImages folder contains both MDIM and raw Viking images. The MDIMs are mosaics and have file names starting with the letter "M". The raw images are actual individual images returned by the Viking orbiters. Raw image files start with the letter "F".

Mars Digital Image Maps (MDIM's) are easy to process because all the necessary (photometric, radiometric and geometric) corrections have already been applied. All that is needed is to enhance the contrast and brightness levels by using the sliders in the map window to yield the best image quality. However, these corrections can blur out details in the original image. This is why many scientists use raw images for research and apply just enough processing as is needed. Because raw images have not been corrected, there is much more noise present in the image (see image below).

As shown in the image below, most of this "noise" can be removed using the PROCESS - Rank Filters - Median (Reduce Noise) option within NIH Image. However, reseau marks (the grid pattern of black dots/pixels across a raw image, as shown belo w) are clearly visible, and are not easily removed within NIH Image. A commercial image processing program, Adobe Photoshop, can easily remove or hide reseau marks by selecting the FILTERS - Noise - Dust and Scratches option. You need to v ary the "radius" and "threshold" values to get the best results for a particular image. To begin, try a radius of 3 to 4. Move the threshold slider until the reseau marks fade away but the image is still sharp.

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