Color correcting by numbers for giclee and other digital printing methods.
Color correcting images on screen for digital output is one of the most
problematic issues in digital imaging. What was a task left to pre-press
professionals in the past and something of no concern with the general public
using film cameras, has now become a must for anyone using a digital camera.
Over the years there have been a number of companies offering color calibration
hardware and software to match what is seen on screen to the actual printout.
Soft proofing (the ability to see an image on the monitor and being able to make
a pretty good judgment about how it is going to look when printed) is definitely
of big help.
This said, the only sure way to be able to precisely color correct is done by
numbers. To make a comparison, take a pilot for example: when visibility is low
pilots rely on what the instruments say to navigate. No matter if it is day or
night, they can navigate without having to see where they are and where they are
going.
The same can be applied to color correction. Depending on a monitor to apply
color changes, especially when subtle modifications need to be made, is not the
best way. All computer screens shift in color from the moment they are turned
on. Numbers do not change.
Photoshop makes it very easy to see what the color measurements are for any
given area in an image. The eye picker will read the quantity of red, green and
blue when passed over the chosen area. For the purpose of this article we will
stay with the RGB primary color space. When looking at a pure black the reading
will be R=0, B=0, G=0. A pure white will be R=255, B=255, G=255, 255 being the
maximum amount in the scale. What is between pure white and pure black? Grey,
which can be any equal amount of these 3 colors, would be for example 122, 122,
122. A lighter grey is 180, 180, 180.
Why is this important? Simply put, very! Let’ s go into something practical: You
are working on a picture of your toddler taken with that high-resolution camera
you got for Christmas. It looks good on the screen but when printed the skin
tones make your child look like he is blushing under 110 F heat. When going over
the skin with the picker the reading is R=200, G=140, B=139. Immediately the red
reading of 200 pops out as a lot compared to the fairly equal and lesser
quantities of green and blue. Without looking at a proof you can see how that
skin will be primarily red. It is OK for skin tones to have a mix of colors and
for a Caucasian complexion to have a higher level of red. A difference of about
60 between red and the other two primaries may be excessive. Also, a warm skin
tone requires a little bit of yellow to be present. In our case the initial
reading for B and G is about equal, meaning they neutralize each other and make
the red stand out as the preponderant color. To add a little yellow we need to
decrease the blue (Blue and Yellow are opposites). In this case a good mix for
such skin tone could be R=190, G=140, B=130.
These numbers are not to be taken literally but as a guide to create a
pleasing balance. Practice taking color readings in different areas of an image.
Look at the printed proof. You will soon learn to correct by numbers and be free
from monitor shifting!
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