Aspects of colour theory
Someone asked me to describe what saturation meant.
Ummm. Yeah. I didn't have an answer.
Luckily Jan Esmann does:
Colorfulness is a non-technical term for the measure of how
intense a specific color appears. Similar, but technically correct terms, are
saturation and chroma (Munsell). Simply put, colorfulness is how much a given
color differs from gray. But what gray? Saturation on the other hand takes into
account that all colors are not equally bright when fully fully saturated: For
example blue is darker than yellow and red. This means saturation is the
colorfulness of a color relative to its own brightness. Laymen will find that
the terms colorfulness, saturation and chroma are used synonymously. The more
colorful a color is, the more vivid and intense it seems, while less colorful
colors appear muted and closer to gray. When all color has been removed and
saturation is 0, the image is called a grayscale image. There is an overlap
between lightness and saturation in that a more saturated color appears
lighter.
Lightness, also called value (Munsell) or tone, is defined
as a colors placement on a brightness scale ranging from black to white. The
Munsell color space, for example, divides the lightness axis, called value,
into ten equidistant steps. Lightness, on the other hand, stems from the HSL
(Hue, Saturation, Lightness) and Lab color spaces where it is used similarly to
Munsell value only in percent. The HSV (Hue, Saturation, Value) color space
speaks not of lightness but of value and uses the word value differently than
Munsell does. In HSV value ranges from black to not white, but to the fully
saturated color. Paints can be made lighter or darker by adding white or black,
but that also reduces saturation. "Tone" is an obsolete term that
stems from darkroom photography to denote the lightness of a specific area of
the print. Yet "tone" is still used in art where light and dark are
built up with charcoal or similar drawing medium
In digital photography lightness can be calculated simply as
(r+g+b)/3. However, that does not take into account that green is brighter than
red and blue darker than red. In the IUV color space the relative brightness of
the color channels is taken into consideration, like this:
i=(76*r+150*g+29*b)/256; It approximately says that green is twice as bright as
red and red is 2½ times brighter than blue.
In painting the term "tone" denotes an intermediate
between gray and pure color. "Tint" denotes a mixture of pure color
with white and "shade" denotes a mixture of pure color with black. In
the real world tint and tone are not a simple as the theory implies, because
though they do not have color in themselves, when white or black are mixed with
a color, the color changes hue. In other words, black in mixtures behaves like
a blueish color. For example if you mix yellow and black you don't just get a
darker yellow, but you get a darker and greenish yellow. Similarly will an
addition of white make a color appear colder.
In software you can digitally create tints and tones by
converting from the RGB color space to IUV or Lab color space and raise the L
(lightness) channel as described above. This will not alter the hue of the
color as when you mix pigments with black or white.
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