What is an Histogram Example for a graylevel

What is an Histogram ? Example for a gray-level image Ø for each gray level, count the number of pixels having that level Ø for each level, a stick represent the number of pixels (can group nearby levels to form a bin and count number of pixels in it) Size : 256 pixels, 8 -bit pixel coding Distribution of gray levels in image [0 ; 255]

Example: compute histogram of an image 8 8 Grayscale image « A » Histogram of image « A » Matrix of gray levels of image « A » 2 2 2 3 2 2 2 0 0 0 2 2 0 1 1 0 2 2 0 1 0 1 0 0 2 2 0 1 1 0 2 2 0 0 0 2 2 2 2 2 Ø Image « A » has 3 different gray levels : 0, 1 and 2. Ø Count the number of pixels for each gray level. Ø There are respectively 24, 12 and 28 pixels for the levels 0, 1 and 2

Cumulated histogram of an image Image « A » Intensity values of « A » 2 2 2 2 2 0 0 0 2 2 0 1 1 0 2 2 0 1 0 1 0 0 2 2 0 1 1 0 2 2 0 0 0 2 2 2 2 2 Cumulated histogram of «A» Ø compute a special histogram thanks to the cumulative sum of histogram elements cumulated histogram. Ø for each gray level “L”, the stick represents the cumulative sum of pixel number for all the gray levels lower or equal than L: levels 0, 1, 2 Øare the cumulated histogram is useful to a lot of image processing thus such as represented by 24, 36 and 64 pixels.