Erik's web

  • Increase font size
  • Default font size
  • Decrease font size

Color Management Part One

E-mail Print PDF

In this part we discuss the need for managing color.

Why do we need color management

Color management is really about predictable color. We want to have the colors on our computer screen to be as close as possible any other medium, like a home cinema projector, a print or even a book. Is this achievable? Yes, sort of.

Calibrating our display is the inital and most critical step

The first thing to know that the colors we see are correct, at least in the sense that we can correlate them to a known standard. A matter of fact is the computer screens vary widely. So to have a known visual reference we need a calibrated display. This is best achieved with hardware tools which fortunately enough are quite affordable. The calibration consists of two steps:

  • Optimizing the display
  • Characterisation of the optimized display

In the first step we adjust the individual gamma curves on the display to get as close to optimal as possible. In the second step we create a mathematical description of how our display represents colors.

 

Color spaces

Overly simplified, eyes can detect three colors, namely RED, GREEN and BLUE. The  sensivity of the rods in the eye for green and red overlap a lot, however:

This image has been copied from Wikipedia:

The above figure indicates that the normal RGB description of our seeing is oversimplified. One way to present the visible colors is to use the CIE 1931 color space chromacity diagram.




This also taken from Wikipedia

The above diagram is nice as we can use it to illustrate some of the problems with reproducing colors. To begin with the edge of the of horseshow represents the spectral colors with wavelenghts in nanometers. The colors along the edge are fully saturated. Moving to the center of the horse shoe the colors are becoming more and more desaturated, that is have more and more white component.

 

If we for a moment consider old "vacum tube" based color television it was based on "phosphors". These so called "phosphors" are compounds which emit light of well characterised wavelenght when excited by electrons. Computer screens normally use something called sRGB, which are based on he sme kind of "phosphors" as used in television. If we plot the coordinates of these "phosphors" in or cromacity diagram we get a trinagle like this one:

 

The triangle defines a gamut. Colors inside the triangle can be reproduced but those outside can not. This is by the way a simplification.

Another set of colors often used is Adobe RGB, it's a slightly larger gamut stretching further out into the greens. The Adobe RGB is shown below as dotted line whereas the sRGB is solid line.

What we can see from this that the words "red", "green" and "blue" may represent different nuances colors. We have also different reds in our perception, crimson, scarlet and bordeaux are all red, but quite different reds.

 

The essential conclusion from this discussion is that we not only need to know how much "red", "green" and "blue" we have but also what those colors actually mean.

 

Monitor calibration and profiling

We want to communicate color. To achieve that we either need to have an agreement on which RGB to use, sRGB is a least common denominator for that, or to ensure that our colors are interpreted correctly at the receiving end, the latter can be achieved color profiles and color management. But... Before doing that we need to know what colors we have. For that we need to calibrate our monitor.

There is no color managed workflow if we don't know what colors we have!

So we need to calibrate our monitor, period. Very sorry, but we need hardware for that. Fortunately monitor calibration hardware is quite affordable to day, so there is no excuse to wait. Calibrate your monitor today!

 

Monitor calibration is a two step process. First we try to optimize the monitor and in the next step we characterize what we achieved. The first part is  to get wite point, black, white and gamma curves for each color optimal. The second part is to create a "color profile" that tells our application how this monitor works. To have a color managed workflow we need to have a calibrated display also in the other end, the calibartions may be different, the differences are handled by color profiles and color management.

Unfortunately very few applications are actually color managed, so it's not just about doing things right but also about using the right tools.

 

The Microsoft way

Microsoft is another spelling for mediocrity. The Microsoft solution to Color Management is sRGB. sRGB is based color television technology and is intended to be a least common denominator. The idea is that everything is converted to television standards. Because everyone uses this least common denominator technology we don't need to care about color management. There are some issue with that philosophy, one is that printers for instance probably never will be able to fully utilize sRGB, as it is based on mixing three additive colors, printers use a different technology based on subtractive colors and black aso known as CMYK, "Cyan", "Magenta", "Yellow" and "Key", the two technologies simply don't match.

Actually, Microsoft inwented a new scheme for handling colors for Vista. The jury is still out, I guess.

 

Is color really critical?

A very good friend of mine was doing some potrait shooting for one of the Swedish international banks. He sent me some of the shoots for an opinion. They were pretty much "orange" in tint. So I asked my friend, are your customers chinese? They sure look that way! I also sent him some pictures i tuned a little bit. My friend really felt that my suggested corrections were for the better. Afterwards he told me that the customers  preferred the original slightly orange hues. So, unnatural skin tones can be OK, so you have a nice tan?

 

Unfortunately a company like Volvo would be less tolerant. Volvo blue is blue, not purple, not violet, blue, Volvo blue, period. Same applies to IBM. A house owner who had his hous painted in pink would probably also have some opinions, even if the house looked good on his uncalibrated monitor.

 

 

 

 

 

Last Updated on Wednesday, 22 July 2009 21:51  

Statistics

OS : Linux u
PHP : 5.2.9
MySQL : 5.0.67
Time : 17:50
Caching : Enabled
GZIP : Disabled
Members : 1510
Content : 72
Web Links : 1
Content View Hits : 371398

Login

Banner1

J!Analytics