| It's time to learn some more about a key concept in graphics: color
(this page is a reading exercise only).
Photoshop often needs to describe colors with numbers - the RGB (red, green,
blue) convention is the most common way of doing this. Photoshop can reproduce 256
levels of brightness (numbered 0 to 255) for each of these 3 primary colors,
giving a total of 256 x 256 x 256 = 16777216 or about 16 million different
colors. (0,0,0) represents black, (255,0,0) represents bright red, (255,255,
255) represents white. Adding primary colors gives the secondary colors: red +
blue = magenta, red + green=yellow, green +
blue=cyan. This is demonstrated in the following diagram which shows
what happens when circular red, green and blue light beams are projected onto a white
screen and made to overlap:
 Such
a diagram is sometimes called a color wheel. Colors on opposite sides of the
color wheel, such as green and magenta, are called complementary colors. Some
of the above statements, such as green + red = yellow, may surprise you,
for your experience mixing paints may seem to contradict this. The explanation is that
paint pigments absorb colors, leading to color subtraction,
whereas the above text and the color wheel describe color addition. Color
addition corresponds to the way your computer screen works - if
the screen's tiny red and green dots are lit simultaneously then you will see yellow.
It also corresponds to the way the human eye works - the eye has color sensing
cells only for red, green and blue - if the red and green sensors are stimulated
simultaneously then you see yellow. Look again at the diagram, and make sure that you can tell the difference
between red and magenta, and between blue and cyan. Note how the diagram
correctly shows that when red, green and blue lights (not pigments) are added
together, the result is white. Can you tell what color the RGB
combination (0,255,255) would refer to? This would be a combination of no
red + bright
green + bright blue, in other words CYAN. When you are
working in Photoshop you can click any part of the image with the Eye Dropper
tool  to 'pick up' the color
of that
pixel
and make it the new foreground color, as displayed in the toolbox (top left here)
 . Instead of using the eye dropper
tool you can also simply Alt-click the image at any time. The forecolor is used
by various tools, such as the airbrush, paintbrush, pencil, paint bucket etc. You can also change
the foreground or background color by clicking their respective squares.
Clicking the small black and white squares sets the foreground color to black
and the background color to white. Clicking the double-headed arrow swaps the
foreground and background colors. |
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