This document discusses image processing techniques including histograms, filters, and the median filter. It defines a histogram as a graphical representation of pixel intensity distribution in an image. Histograms display data distribution and frequency through bins representing intensity value ranges. The importance of histograms is that they provide a visual representation of data and can display large amounts of information. Filters are used in image processing to remove unwanted information or amplify features of interest. The median filter specifically removes noise by replacing pixel values with the median of neighboring pixels, making it effective for "salt and pepper" noise removal. It works by finding the median value in a pixel neighborhood matrix and using that value to smooth the image.