A printed page can look like a smooth field of ink, yet it is built from tiny separate dots. Resolution names how densely those dots are placed in a physical area. At low resolution, the eye can pick out the individual marks; at high resolution, the dots are so small and close together that they blend into a continuous-looking image. section 1.2
Dots per inch (dpi) makes the density concrete. A 600 dpi printer places 600 dots along each inch in both directions, or 360,000 dots in a square inch. At 1,200 dpi, that becomes 1,440,000 dots per square inch. More dots are not merely a larger number: they provide a finer grid on which letters, lines, and images can be approximated. section 1.2
A page made from dots
An 8.5 by 11 inch page printed at 1,200 dpi contains 1,200 × 1,200 × 8.5 × 11 = 134,640,000 possible dot positions. In a black-and-white printed page, each position may hold black ink or no ink. A tablet or computer screen may use fewer dots per inch, while allowing its pixels to show grays and colors as well as black and white. section 1.2
Figure 1.3 Three different resolutions
Compare the same capital A at 60, 30, and 15 dpi. As the grid becomes coarser, its steps become easier to see and the letter becomes blockier. section 1.2
Resolution matters when a continuous shape must be drawn on a grid. A shallow line can be approximated by choosing the dot nearest the line in each column. The same line looks better when drawn at higher resolution because it has more, smaller dots. For steep lines, choosing one dot in each row works better; horizontal and vertical lines are the simplest special cases. section 1.3
Even a denser grid has trade-offs. At low resolution the dots are visible, and lines of different slopes can have different apparent densities: a 45° line covers a longer distance than a horizontal line while using the same number of dots. Shades of gray offer another way to make line edges appear smoother, rather than relying only on black-and-white dots. section 1.3 section 1.3
The same shape may need to appear on a 200 dpi screen and a 1,200 dpi commercial printer. Rather than storing a shape as a fixed collection of tiny line segments for one grid, it can be described in terms such as a circle’s radius and position, then converted into the appropriate pixels or ink dots for the chosen device. section 2.0
