The field of raster image processing
digital-image-processing covers a broad range of different algorithms and techniques used to process raster images. For example they are often used to modify digital camera images, correcting for contrast, saturation, color, red eye, etc.
In a geospatial context, digital signal processing is often used with aerial imagery and remote sensing imagery to enhance images (eg. by changing their colors or contrast); to match adjoining images with different contrast; to highlight potential features (eg. edge detection); and to correct for map projections and oblique camera views.