Color managment - Please sticky if worthy

Started Mar 29, 2013 | Discussions thread
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fft81 Contributing Member • Posts: 945
Color managment - Please sticky if worthy


This document is meant as a short and right to the point write-up about color management. There are 3 things that photographer has to work with that need to be profiled, Camera, Monitor and Printer. One big misconception is that they are being calibrated to match each other. In reality, they are all calibrated to match color codes in a standard color set. By all matching the same color set they also match each other. Therefore we can talk about calibrating the camera, monitor and printer sparely, but to the same standard.


The sensor in the camera interprets colors differently, varying from onecamerato another and it even interprets colors differently depending onambient light. Camera’s white balance feature is meant to compensate for certain cases of lighting conditions, but white balance is just an approximation. One can use color checker to establish known colors and then in software factor out the lighting and camera effects from the final image. In reality, camera measures intensity of red, green and blue light falling on the sensor. Then by making a guess about the energy spectrum of ambient light the camera interprets the measured RGB intensities to determine what color to assign to a given pixel. RAW file records intensity measured by each pixel, JPG uses white balance setting to record cameras guess of color of each pixel based on white balance setting you chose. By taking photograph of color checker one can create a much more accurate correlation between the intensity of light that each pixel measured and the color of that pixel in post-production software. The end goal is to have the color values of the output picture match the color values of the object you photographed. You can think of it this way, each color in real life has a value; camera sees light reflected off that object and records the value which is the sum of values of incident light and color value of the object. Using color checker you can calculate the color value of incident light, subtract it from recorded value and end-up with true color value of the object you photographed.


Now that you have a file in your computer, the color values within which match the color values of the object, you need to be able to reproduce those colors on paper through your printer. How printed colors look is effected by yourprinter, ink set your printer uses, the paper your printer usesand the lighting conditions of the area when you view the print. Usually you cannot predict lighting conditions of where the print will be viewed, so printer profiling only takes into account the ink and paper combination. By printing a set of color patches the calibrating device like colormunki knows how colors should look like on paper and by measuring the printed patches colormunki knows how they actually look. As the result colormunki can generate a correction table, which is called ICC profile, which the print driver uses to print colors more accurately. For example if RGB value of a patch to be printed is 134-126-231 but the measured value of printed patch is 120-110-254, then the driver knows that when it wants to print 120-110-254 it needs to tell the printer to print 134-126-231. Most stock/canned profiles supplied by printer manufacturer will be more accurate that profiles you can generate with colormunki, but they are only available for OEM inks and limited number of papers. Hence you can use CM to make profiles for printer-ink-paper combinations that OEM maker does not provide.


Biggest advantage of color calibrator like ColorMunki is that it can calibrate your monitor. This will let you see colors that are a close match to what you print, but you will never have 100% match. How you see colors on the monitor is effected by several factors:Ambient light, white point of the monitor, luminance of the monitor and color profile used by computer. You use color profile to factor out the variations of other factors. Most monitors will have its luminance set too high and at that setting monitor physically cannot display as many colors as your camera can capture or your printer can print. The luminance value which will give you widest color gamut on your particular monitor will be different than that of mine so I cannot tell you what value for luminance to use, however values between 60 and 120 are common. For best results your monitor luminance should be set to the value that gives highest color gamut AND you should be using different color profile for different lighting condition. For example: if during the day your room is lit by sun coming through your window, in the evening it is lit by combination of sunlight and table lamp and at night it is lit by main ceiling light; then you should have 3 color profiles for your monitor. Here is a write up how to change color profiles used by your computer under windows 7.

Copy/Paste from here:

    To apply an existing ICC profile (an ICM file created by some calibration process), do the following -
    Control Panel / Display / Change Display Settings / Advanced Settings / Color Management / Color Management  / Devices / select one of your displays

/ click "use my settings for this device"

/ if necessary add the applicable profile to the "Profiles associated with this device" box using the "Add" button (if your profile is not already listed but is available somewhere on the network or computer) / click on the correct profile in that box and click "Set as Default Profile".

Usually profiles are stored here: “Windows>System 32>Spool>Drivers>Color”
*1 the CM dialog boxes don't label your displays the same way as other dialog boxes, they seem to lose the manufacturer and model number info that is available elsewhere, so your ABC model nn display comes up as Display: 1. Generic PnP monitor .  Also note that at least on my system, display '1' was in fact display '2' in other display settings dialog boxes, and vice versa. 
Here's the hidden bit of help file...

To enable or disable calibration loading by Windows , you must be logged on with a user account that has administrative privileges.

  1. Click to open Color Management.
  2. Click the Advanced tab, and click Change system defaults .
  3. Click the Advanced tab in the Color Management - System Defaults dialog box, and do one of the following:
  • To enable Windows to load display calibrations,select the Use Windows display calibration check box.
  • To prevent Windows from loading display calibrations, clear the Use Windows display calibration check box.
  1. Click Close in the Color Management - System Defaults dialog box.
  2. 5.     Click Close in the Color Management dialog box.

If any one wants to add step by step instructions on how to do color correction in post using photograph of color checker, be my guest. Too many different software packages for me to type it all up...

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