AlMustansiriyah University Faculty of Engineering Computer Software Engineering

Al-Mustansiriyah University Faculty of Engineering Computer & Software Engineering Department Digital Image Processing lab. Experiment No. (5) Image Histogram and Its Equalization Aim: The image histogram is calculated and image contrast would be improved or enhanced using the histogram equalization. Theory: Histogram indicating the number of times of each grey level occurs in the image or simply it is the frequency of occurrence of gray level values. Histograms are so useful that modern digital cameras often provide a realtime histogram overlay on the viewfinder to help prevent taking poorly exposed pictures. Linear (Contrast ) Stretching The piecewise linear stretching function can be used to enhance image histogram as explained in the following example: 15

Al-Mustansiriyah University Faculty of Engineering Computer & Software Engineering Department Digital Image Processing lab. “pout. tif “image is a somewhat low contrast image. To see the distribution of intensities in pout. tif, you can create a histogram by calling the imhist ( ) function. 16

Al-Mustansiriyah University Faculty of Engineering Computer & Software Engineering Department Digital Image Processing lab. Histogram Equalization: The histogram equalization formula is another method of contrast enhancement. It is an operation that transforms an image with arbitrary histogram to one with flat histogram as explained in the following program. Requirements: 1. Write a MATLAB (use built-in functions) program to find and plot the histogram of “ 5 ind. tif image” before and after equalization. 2. Re-compute the contrast stretching operation of step 1 and display the enhancement image with i 1 ts 7 histogram. Which method is better