A page that looks like a smooth letter or photograph can be built from tiny separate marks. On a screen, these marks are usually square dots called pixels—short for “picture elements.” Each pixel can be chosen as black, white, gray, or a color; together, many choices make an image. section 1.0 section 1.2
Pixels make digital pictures discrete: instead of placing ink anywhere at all, a system chooses from positions in a grid. More positions in the same area mean higher resolution. When pixels are small and tightly packed, the eye cannot resolve the individual dots; when resolution is low, curves, letters, and pictures look blocky. section 1.2
A page made of dots
At 1,200 dots per inch, one square inch contains 1,200 × 1,200 = 1,440,000 dots. A US Letter page at that resolution contains 134,640,000 dots. A printer may use many black-or-white dots, while a tablet screen may use fewer dots but give them gray or color values. section 1.2
Figure 1.3 Three different resolutions
Compare the same capital A at 60, 30, and 15 dpi. The increasingly coarse grid makes the letter’s edges visibly stepped, showing why resolution changes the appearance of pixel-built shapes. section 1.2
Pixels are the raster form of a page: a grid of individual marks. Letters and drawings may begin as vector descriptions of shapes, then be converted into pixels so they can be shown or printed. Choosing pixels along a line or inside a character is therefore a practical way to approximate continuous-looking forms with dots. section 1.5 section 1.6
