Brightness equalization between different images

1. What does image equalization do?
2. Does histogram equalization always increase contrast?
3. What is brightness in image manipulation?
4. What is the effect of histogram equalization on images with low contrast?

What does image equalization do?

Histogram equalization is a method to process images in order to adjust the contrast of an image by modifying the intensity distribution of the histogram. The objective of this technique is to give a linear trend to the cumulative probability function associated to the image.

Does histogram equalization always increase contrast?

Histogram equalization is used to enhance contrast. It is not necessary that contrast will always be increase in this. There may be some cases were histogram equalization can be worse. In that cases the contrast is decreased.

What is brightness in image manipulation?

Instead, in terms of digital image processing, brightness is more properly described as the measured intensity of all the pixels comprising an ensemble that constitutes the digital image after it has been captured, digitized, and displayed.

What is the effect of histogram equalization on images with low contrast?

This allows for areas of lower local contrast to gain a higher contrast. Histogram equalization accomplishes this by effectively spreading out the highly populated intensity values which are used to degrade image contrast.