A printed or displayed page is built from tiny locations: dots. On a printed page, each dot may be white, meaning no ink, or black, meaning ink. When dots are small and closely packed, the eye blends them into letters and pictures; when they are too large or sparse, individual blocks become visible. section 1.2
Resolution counts how many dots fit in a space. A 1,200 dpi printer places 1,200 × 1,200, or 1,440,000, dots in each square inch. An 8.5 × 11-inch page at that resolution contains 134,640,000 possible black-or-white dot locations. Screens commonly use fewer dots per inch, but their dots can show colors or shades of gray. section 1.2
Figure 1.3 Three different resolutions
Compare the same letter at 60, 30, and 15 dpi to see how lowering the number of dots makes its edges visibly blocky. section 1.2
Dots also provide a practical way to draw a line. First define the line by its two endpoint coordinates. Then choose dots near that ideal line. For a shallow line, selecting one dot in each column gives a better approximation than selecting one dot in each row; for a line steeper than 45°, reverse that choice. More, smaller dots make the same slope look smoother. section 1.3
A dot-based line involves a few simple decisions:
- Use the endpoints to specify the intended line segment. section 1.3
- For horizontal lines, mark one dot in each column; for vertical lines, mark one in each row. section 1.3
- Choose columns for shallow slopes and rows for steep slopes, with either choice working at 45°. section 1.3
- Use shades of gray when available to make an edge appear smoother than black-and-white dots alone. section 1.3
A six-column line
For the segment from (1, 1) to (6, 3), choose one dot in each column from 1 through 6 whose center is nearest the intended line. The result is only an approximation, but increasing the resolution supplies more and smaller dots and improves its appearance. section 1.3
