Lighting manipulation by histogram

I did a post about segmentation (in portuguese), in that post I cited a histogram's equalization, and, I'm working with enhancement for my DIP class, so I will show a very simple technique here.

I use just Scilab and SIVP for develop my codes (search for scilab and sivp tags here in the blog).

Ok, let's do a offset manipulation in the image's histogram. This technique consists in add or subtract a constant value in all pixels.

See the picture.

Its histogram is this.

Ps.: The histogram is the number of pixels for each value (send comments for any question).

This is a lighter image, and its histogram is concentrate in higher values. Thus, let's subtract a constant value 50 of each pixel.

The result.

Old imagem | New image.

And the hew histogram.

The technique is very simple, but the simplest form is the best in many cases.

If anyone wants more about histogram's manipulation then send me comments.