Technical data

94 Color and Input/Output Options
A grayscale image looks like what we would call a “black and white”
photograph, which properly speaking has many levels of black and
white (not just two, as in a monochrome line drawing). On computers,
Grayscale mode stores 256 shades of gray or levels of lightness. A
value of 0 represents pure black, a value of 255 pure white. Sometimes
we speak of the “tones” in a grayscale imageit’s just another word for
the different “values” or “lightness levels.”
To understand HSL, imagine the difference between watching a TV
program on a black and white set as opposed to a color set. It’s the
same color signal, right? But the black and white set doesn’t reproduce
the color. What it does pick up is the grayscale or lightness channel of
the signal. In the same way, any color image in PhotoPlus has a channel
that stores lightness information. The “L” in HSL stands for Lightness.
To repeatand this is important when it comes to understanding topics
like maskinglightness and grayscale values (and for that matter tones,
luminance, and brightness) all refer to the same thing.
The additional Hue and Saturation channels in HSL mode together
store the color information that’s missing from a simple grayscale
image. Like Lightness/Grayscale values, Hue and Saturation channel
values are expressed in numbers, ranging from 0 to 255. (If you’re alert,
you’ll note that 256 is equivalent to 8 bits of information, so H+S+L
has three 8-bit channels totalling 24 bitswhich is where the “24” in
“24-bit” comes from.
Hue refers to the color’s tintwhat most of us think of as rainbow or
spectrum colors with name associations, like “blue” or “magenta.” A
color wheel (like the one in the PhotoPlus
Adjust Color dialog) is useful for representing
the spectrum of hues as a continuous cycle, like
a clock. The hue “red” is arbitrarily assigned
the value 0 at a certain position, and the values
run around the circle. Saturation describes the
color’s puritya totally unsaturated image has
only grays.