Histogram Matching
The Histogram Matching (also called Histogram Specification) algorithm generates an output image based upon a specified histogram.
Background
The process of Histogram Matching takes in an input image and produces an output image that is based upon a specified histogram. The required parameters for this algorithm are the input image and the specified image, from which the specified histogram can be obtained.
The algorithm works as follows:
The histograms for the input image p(f) and the specified image pd(g) are generated. Here, the desired histogram of the specified image is denoted as pd(g). Cumulative histograms  P(f) and Pd(g) are then generated using the following equations:
Equation 1
<math>
P(f) = \sum_{k=0}^fp(k)
</math>
Equation 2
<math>
P_d(g) = \sum_{k=0}^gP_d(k)
</math>
where f and g are the pixel intensity levels.
The transformation function is obtained by choosing g for each f, such that if g > f, then Pd(g) > P(f). The transformation function is then applied to the input image to produce an output image by remapping the pixel intensities. The objective is to find a transformed digital picture of a given picture, such that the sum of absolute errors between the intensity level histogram of the transformed picture and that of a reference picture is minimized. Refer to Figure 1.
References
Rafael C. Gonzalez and Richard E. Woods. Digital Image Processing. AddisonWesley Publishing Company, 1992, pp. 173182
Jae S. Lim. TwoDimensional Signal and Image Processing. PrenticeHall, Inc., 1990, pp. 453459
Image types
You can apply this algorithm to both color and blackandwhite images, as well as 2D and 3D images.
Applying the Histogram Matching algorithm
To use this algorithm, do the following:
 Select Algorithms > Histogram Tools > Histogram Matching in the main MIPAV window. The Histogram Matching dialog box (Figure 5) appears.
 Complete the information in the dialog box.
 Click OK. The algorithm begins to run, and a progress bar appears momentarily with the status. When the algorithm finishes running, the progress bar disappears, and the results appear in a separate image window.
Histogram match <File name> to

Select the specified image pd(g) from the list box


New image

Shows the results of the algorithm in a new image window
 
Replace image

Shows the results of the algorithm in the same image window
 
OK

Applies the algorithm according to the specifications in this dialog box.
 
Cancel

Disregards any changes that you made in the dialog box and closes this dialog box.
 
Help

Displays online help for this dialog box.
