How to Normalize a Histogram in MATLAB?

Histogram normalization is a technique to distribute the frequencies of the histogram over a wider range than the current range. This technique is used in image processing too. There we do histogram normalization for enhancing the contrast of poor contrasted images. 

Formula:

Here ./ and .* means operation has to be performed element-wise.

Steps:

• Read the image.
• Convert color image into grayscale.
• Display histogram.
• Observe maximum and minimum intensities from the histogram.
• Change image type from uint8 to double.
• Apply a formula for histogram normalization.
• Convert back into unit format.
• Display image and modified histogram.

Example: 

Output:

Figure: Original histogram

Figure: Normalized histogram

Figure: Images before and after normalization

Code Explanation: 

• First, we read the image using imread( ) function.
• After reading the image, we convert it into the grayscale format.
• After converting it into grayscale, we displayed the image and its histogram.
• Maximum and minimum intensity is noted from the histogram.
• The image data type is changed from uint8 to double, to facilitate the calculation steps.
• Apply the formula of normalization.
• The image data type is changed back to uint8.