144 PART 3 HOW THE DIGITAL DARKROOM WORKS
How Software Manipulates Images
on the Pixel Level
The humongous advantage of using numbers to represent images is that you can lighten an image, darken it, bring out contrast, sharpen it
or blur it, turn it upside down, or transform it into a psychedelic abstract, all by using simple arithmetic. It’s not so simple that we can sit at
a computer with the Mona Lisa on the screen and subtract numbers from the color values in Mona’s portrait, turning her smile into a frown.
It would be an excruciating job, the kind of job computers are made for. A PC can calculate a frown job on Mona in less than 10 seconds.
It’s all just a numbers game.
Your digital camera records your digital photo as a set of tiny pixels. As you look closer at a photo, though, you begin to see the pix-
els as jagged edges and then squares. What you thought were distinct lines and boundaries turn out to be more gradual transitions
between colors.1