Hey @victoriaxl, I am very happy you read the blog entirely, histogram equalization basically deals with increasing the contrast of the image. The image was converted to grayscale so that we deal only with black and white.
Imagine you have done a x-ray but the quality is poor, means it is difficult to distinguish between the white part and black. So if somehow we manage to equalize the image in such a way that a brighter part appears brighter and the dark part appears darker, we can easily study the x-ray.

Histogram equalization thus have a great scope in image processing and computer vision
Hope my example of x-ray has made it more clear. Anyways if you have any other doubts feel free to ask I am a LOSER I have nothing better to do 😁 😁 😁 ..............