The primary tool that’s used to evaluate the tones in a digital image is the histogram. A histogram is a graphical representation of the distribution of the tones in an image. It consists of a graph that ranges from pure black on the left to pure white on the right. In between are all the shades of gray from almost black to almost white. Imagine 256 side – by – side columns, one for each of the individual tonal value that a histogram represents. The columns start with black (0) on the left and end with white (255) on the right.
In between are 254 other columns representing all the shades of gray between black and white. Together these 256 levels equal the sum total of the tones in an image. The height of a column is governed by the number of pixels in the image having that particular tone. If the image includes lots of neutral tones, then the columns around the middle of the histogram are taller. Because these columns are standing right next to each other, they form a graph when viewed as a group. This is basically an important concept to an infographic company that makes nice infographics.