186 PART 4 HOW DIGITAL PRINT-MAKING WORKS
When the light waves hit a polarizing filter, most of the waves are blocked by the filter’s microscopic
structure, like the blades of a Venetian blind that let pass only those light waves vibrating in a specific
direction. The polarizer has some leeway in the waves it permits through, which is why the LCD screen
can produce different shades of red, blue, and green.2
The polarized light next passes through a sheet made up of thousands of liquid crystals in a grid pat-
tern. One of the properties of the crystals is that they twist when an electrical current passes through
them, and the light rays follow the curve of the crystals. The stronger the current, the greater the distor-
tion until some of the light waves leave the crystal panel vibrating 90° from their original orientation.3
Light waves from the different cells—some still vibrating in their original orientation, some turned 90°,
and the rest twisted at some point in between—encounter a second filter mounted so it polarizes light
in an orientation 90° from the direction of the first filter. Light that underwent a full 90° twist passes
through the second filter completely to create a dot of red, blue, or green. Light waves that were not
distorted at all are blocked totally, producing black dots. All the other rays of light, being twisted to
varying degrees, pass through the second filter partially, producing some greater or lesser shade
of color. Our vision perceives the colors of the adjoining light rays as a pixel of one color from the
thousands this method can create.5
How a Camera’s
LCD Displays Photos
Long before your photo appears as a print, it has a brief life on a liquid crystal display (LCD) screen,
either the small one on the back of most digital cameras or the larger screens on your laptop or desktop
computer. LCD screens and their older, more cumbersome cousin, the cathode ray tube (CRT), use
different methods to produce the same three colors that blend into full-color pictures. But curiously, they
don’t use the same colors that photo-quality printers use. All color screens use red, green, and blue,
which is why you’ll hear them referred to at times as RGBdisplays. Printers use two off-shades of red
and blue (magenta and cyan) and a standard yellow—at least to begin with. Now the more overachiev-
ing color printers are adding more colors and subtler hues to reproduce richer and more accurate color
prints. We’ll get to them in the next couple of illustrations. For now, let’s look at your pictures on an LCD
screen, whether on a desk or camera.
(^4) The light passes through sets of red, green, and blue filters grouped together to form colored pixels.
A fluorescent panel at the back of an LCD screen emanates a white, even light. Each light wave
vibrates as light waves normally do, in all directions perpendicular to the direction it’s traveling.
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