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1. Re: What exactly does monitor calibration do?
Noel Carboni Nov 23, 2010 10:57 AM (in response to avpromedia)function(){return A.apply(null,[this].concat($A(arguments)))}
avpromedia wrote:
Why not turn on color management in windows so that all software are automatically color managed?It just doesn't work that way; it's just too simplistic a thought. Windows does provide the ability to do color management right at the GDI interface via calls like StretchBlt() (but not with OpenGL), but the key thing is that the application has to provide a source color profile. You could make the argument, I suppose, that the system could automatically take (assumedly sRGB) display data and transform it to the monitor's profile, but where would that leave color-managed apps? The sRGB profile is more limited than many modern devices can handle, so where would that leave people with wide gamut monitors, for example.
You have pretty much everything right conceptually. The calibration process loads tables into your video driver/video card to get your gamma response just about right. The monitor profile is used by the software doing the actual image display.
-Noel
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2. Re: What exactly does monitor calibration do?
emil emil Nov 23, 2010 3:23 PM (in response to avpromedia)The correct terms for what you described as first and second are Monitor Calibration and Monitor Characterization or Profiling.
Calibration brings the monitor to a desired state by changing the behavior of the monitor or said in other words, alters how the monitor displays colors.
During the calibration process the monitor calibration software first changes directly or through the user all that is possible with the hardware controls of the monitor to bring its display to the desired state and then whatever was not possible with the hardware controls will be accomplished automatically also as much as possible by using the video card.
Profiling is first checking and then describing the display characteristics of the monitor in a monitor profile file. A monitor profile file, among other things, describes how the monitor displays color values like the RGB numbers. Profiling doesn't change the monitor behavior. The profile file is used by the color managed programs to change the color appearance of the images they use by sending the appropriate color values to the video card. These color values may be different from the actual color values of the image.
On theory, you don't need calibration in order to have properly characterized monitor. All the color managed programs need, is a monitor profile that describes how the monitor displays color values. However on practice if the monitor is calibrated as much as possible to a desired state, it can have much more and better display capabilities than a monitor without calibration. A desired state of a monitor is when its full capabilities can be used with certain display targets. These targets are specified by the user and are usually the white and black points, color temperature, and gamma.
To illustrate how a monitor without calibration can be a problem, I will give the following example. If you reduce only one of the RGB signals significantly, lets say the Blue, by using the hardware controls of the monitor then all neutral colors will become yellowish. With such monitor display, to get neutral colors, the color managed programs have to reduce also the other two signals Red and Green using the video card to the lowest denominator of the reduced Blue and this in general will limit the range of the entire color space available on your monitor. And since color management is about simulating on your monitor other color spaces (device and non-device specific) if you have limited display capabilities your monitor will not be able to adequately simulate other color spaces no matter how well the color managed programs try to achieve that. And also, as you already guessed that, in this example the non-color managed programs will display everything yellowish on such monitor because they don't have color management capabilities to correct it.



