Contrast Enhancement

Features:

Improves the visualization of the image through image-improving algorithms such as Image Adjustment, Histogram Equalization, and Contrast-Limited Adaptive Histogram Equalization (CLAHE). The algorithms convert the low-contrast image into a higher contrast.

Image Adjustment increases the contrast of the image by mapping the values of the input intensity image to new values, by default, 10% of the data is saturated at low and high intensities of the input data.

Histogram Equalization performs image histogram equalization. It enhances the contrast of images by transforming the values in an intensity image so that the histogram of the output image approximately matches a specified histogram (uniform distribution by default).

Contrast-Limited Adaptive Histogram Equalization (CLAHE) performs contrast-limited adaptive histogram equalization. Unlike Histogram Equalization, it operates on small data regions (tiles, default 8x8) rather than the entire image. Each tile's contrast is enhanced so that the histogram of each output region approximately matches the specified histogram (uniform distribution by default). The contrast enhancement can be limited to avoid amplifying the noise which might be present in the image.

Notice: to apply these algorithms, the image will be first converted into a pseudo-RGB mode with random channels.

Steps:

1.       Select Filtering and Enhancement → Contrast enhancement → Image adjustment (Histogram Equalization, or CLAHE).

2.       After completion, click OK and visualize the image in the pseudo-RGB format.

3.       This resulting image can be returned to the original by using Filtering and Enhancement →Remove all Filters and Enhancements or Reset button.  

Reference:

Zuiderveld, Karel. “Contrast Limited Adaptive Histogram Equalization.” Graphic Gems IV. San Diego: Academic Press Professional, 1994. 474–485.