vs. CMYK Colour Gamuts
range of colour that can be perceived (e.g. by the human eye) or displayed
(e.g. by a computer monitor or printing press) is a colour gamut. Different
devices have different colour gamuts. That is, they can produce a range
of colours that vary depending on the device. That is why a colour image
may look very different when viewed on different monitors, and why,
although both Macintosh and Windows operating systems recognise millions
of colours, only 216 of those colours are considered "safe"
for web use - they are the colours that can be consistently reproduced
on both Mac and Windows-based computers. To make things even more complicated,
colours are created and described differently depending on how they
are displayed. Computer monitors, which display in RGB, are also described
as using an additive colour model (add colours together to create white),
while printed materials, using CMYK to create colour, can be described
as using a subtractive colour model (subtract colours to get white).
RGB stands for Red, Green, Blue. Computer monitors, video cameras, television
sets, etc. create colour using the RGB model. Under this model, a device
will add varying amounts of red, green and blue light to a black background.
On a colour monitor this translates into having three possible light
sources for each pixel on screen. To get white, 100% of each colour
is transmitted. All other colours are created by varying the amount
of red, green and blue displayed. RGB is considered an additive colour
model. When there are no colours, the result should be black.
CMYK stands for Cyan, Magenta, Yellow, and Black. Four-color printed
materials are created by combining various amounts of cyan, magenta
and yellow inks. Theoretically, 100% of each of those colours should
create a true black, but usually the result is a muddy, dark brown colour,
so black is added as a separate colour To get white (paper), no colours
are added. CMYK is therefore considered a subtractive colour model.
Because of the difference in how monitors and printed materials create
colour, there are often surprising differences between what is created
on screen and what the output actually looks like. Some computer programs
(such as Photoshop) have gamut warning capabilities, to let the user
know if they have created a colour on screen that can not be accurately
reproduced in print. There are also several monitor and printer calibration
devices and software available. Currently the most accurate way to produce
colour is to refer to known benchmarks such as the Pantone Colour System.
Systems like this ensure that the designer and the printer have a common
reference, regardless of how something looks on screen. When working
with photographs, get accurate proofs (Kodak approval, matchprint, or
similar) before the job goes on press.