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Color Correction Editor
RGB Color Space
On a computer monitor, colors are generated by means of red, green and blue dots illuminated at differ-
ent intensities. If you look closely enough at the monitor, you can see these dots. The red, green and blue
(RGB) variables can be stored digitally as bytes with values from 0 to 255. The notation (255,255,255)
means “white”, (0,0,0) means “black” and (0,255,0) means a fully saturated “green”. The brightness not
only of the resulting colors is also described by the RGB value sets: (25,25,25) would be a dark gray,
(200,200,200) a light gray.
Many graphics programs use the RGB model to define colors.
YUV Color Space (YC
b
C
r
Space)
Television was originally black and white. All the information was transmitted in one signal, the lumi-
nance signal (Y), which permitted the display of the necessary shades of gray. When color television was
developed, it still had to operate on the many existing black-and-white TV sets. For this reason, two
“color difference signals” were added to the Y signal: C
b
(analog: B-Y; U) and C
r
(analog: R-Y; V).
These three components form what is often called the “YUV” signal. From this signal, red, blue and
green values can be computed that guarantee the correct reproduction of color on the color monitor.
Stored digitally as bytes, the value of each component can in theory range from 0 to 255. The actual
ranges of values, however, are limited by CCIR Standard 601:
Y (16 to 235)
C
b
, C
r
(16 to 240)
Mathematically speaking, the two color spaces (YUV and RGB) describe the same space. However, the
different range of values results in a very different spatial resolution. Moreover, specific colors are “not
possible” in the RGB space but can be produced in the YUV space. See also “Legalizer” on page 761.