A Practical Example of Grayscale Calibration
Open the image you want to calibrate in Adobe Photoshop (fig. 4.2 shows my example).
The first thing to do is to open the Levels window (Image > Adjustments > Levels) in order to make a basic adjustment to the tonal range so that it extends from black to white (see fig. 4.3).
The Input histogram, in the center of the window, shows the “pixel pile”—i.e. which shades of gray are present in the image, and the relative quantity of each one. Think of it as being made up of 256 vertical columns, one for each shade, beginning with black on the far left and ending with white on the far right, and that each column is filled proportionally according to the number of pixels there are of that particular color. ...