How To

Why a well calibrated Monitor is the key ...

White Fur, III

Monitor Calibration - Do we really need this? Non-professionals often think, that all these things are only important for commercial photographers doing offset printing. While in the RGB color space 16.7 million colors are available, in the CMYK color space in comparison, "only" approx. 264,000 colors are available. This results in the fact that photographs on the screen (RGB color space) essentially looks different, than photographs which are printed in the CMYK color space using an ink jet printer, professional printing machines etc. In addition the impact on the optical impression due to different papers, inks etc. is more or less severe.

This document should simply give a short overview on the underlying problems and refer to the connected challenges. In the end it is up to you to decide "how far you want to go".

The calibration procedure described below will:

Accurately calibrate the system gamma value, tune the gray balance (using the Adobe Gamma (Win) or Calibrate (Mac) utility) and enable Photoshop Color Management. First, in Photoshop one has to go to the dialog and set all the six profile options to "Ask when opening". Photoshop will then ask every time an image is opened what to do, in case the image does not have a Photoshop profile included (or there is a profile mismatch). This question is something that will be really appreciated later on. One should do it, now. Three things to take into account before we start:

Let the monitor to stabilize at least 1 hour (very important !).

Set up the normal room lighting that you will be working with. If possible make it mid level or below and eliminate glare.

The person doing this "optical calibration" should be fresh and well rested

Here we have to distinguish between normal daylight in the shade with a theoretical color temperature of 6500 K or image proofing light sources - sometimes called "norm light" - which have 5000 K. Average noon daylight would be around 5500 K. This will be important later.

The simple way is to use dedicated software to calibrate the system. While the basic principles are the same, some practical steps are slightly different, if one compares Windows and Mac OS X systems. Let's have a look at Apple's "Display Calibrator" first.

opens the software calibration tool. Now, one is guided step by step through the calibration procedure. In a first step the display's native response is determined. It has to be said here, that the adjustment using the sliders is rather tricky, as it depends mainly on one's personal impression ("Match the grey in the middle with the surrounding grey"). The target gamma value can be adjusted using the slider, seen here. As mentioned, values between 1.8 and 2.2, where the latter one is used for a "Standard PC" system. In the next step the target white point has to be set: Here D65, 6500 K is the value to be chosen for "daylight". The final steps are to define for which users the created profile will be accessible, to name it and save it. OS X is placing the generated profile in the right system environment and is automatically activating the profile. A good way of keeping the profiles organized is the . All profiles installed on the system are organized by category (screen, printer, scanner, etc.) and detailed information including graphical representation of the color space is available.

For users of Windows operating systems there is the Adobe Gamma Utility

Adobe Gamma can be run directly from the menu. Similar to Apple's solution a clear and easy to follow user interface is guiding through the necessary steps. The first choice is between a "Step-by-Step" Wizard or via a "Control Panel". Let's have a look at both of them. A clean screen shows all important options and settings. On the top a field for a personal description note. The rather cryptic term "Phosphors" allows to chose to monitor type. Either one or three gamma sliders should be positioned in a way to have a match between the field in the center and the surrounding back-ground. Typically for a Windows system the desired gamma value is 2.20. The bottom field allows to set the hardware white point, 6500 K for daylight in this example.

Saving the profile under a meaningful name is the final step here. As before, I recommend to include the monitor type and the date of the measurement in the name to avoid confusion later. The Wizard is practically doing the same thing, with the only difference that all steps are presented in separate screens. With the idea to help the not so trained user, all steps are explained in detail. Like before, here the selection of the monitor type and then the three gamma sliders together with the desired gamma value. Please remember that these sliders must be viewed at such distance that the dithering is fully averaged by the eye, this is about 1 to 2 meters away (3 to 6 feet). The monitor may have an imbalance between the gammas of the red, green and blue guns with the effect that the gamma chart will show this very easily. The next step is to correct this gray balance. The "view single gamma only" check box has to be unchecked here. To start with, one should make a large change to the red slider in order to familiarize how it affects to the gamma chart. In addition to an overall gamma change one can notice hue changes in both the continuous tone portion and the dithered portions of the swatches. Then the red slider is used to remove -or- to balance as much as possible the reddish tint between the continuous tone portions and the dithered portions of all the gray swatches.

Now, the blue slider is adjusted to remove -or- balance as much as possible the bluish tint between the continuous tone portions and the dithered portions of all the gray swatches. It is unfortunately possible that the gamma match is not good anymore. In this case the overall gamma can be adjusted by playing with the green slider a little. This will offset the color balance so one will have to repeat the red-slider, blue-slider adjustment as described above. The total procedure is a repeating game of adjusting and evaluating until one comes up with an accurate result. It is somewhat tedious but well worth the effort in case no hardware calibration is available. Before saving the final profile, the hardware white point is set and a direct "before vs. after" comparison should convince the user that everything is as expected. One point that can easily be forgotten is to verify that the "Adjusted White Point" is set to "Same as Hardware"

As before mentioned already, it's very important to "tune" the measuring device - the human eye according to the measuring environment: View the outside real-world daylight scene for a minute or two in order to adapt your vision to the true daylight and only after that one should go through the procedure described. Also keep in mind, that to total procedure should not take too long, as the human eye quickly gets tired.

In order to get better results and guarantee reproducible results "Hardware Calibration" is needed.

Why do we need to use hardware if software can do the job ? The problem is the interface human - computer. The "weak" point of the above mentioned procedure is the adjustment by eye of the color and brightness fields in Apple's Calibrate or Adobe Gamma. For one person it might work pretty well, while for somebody else it might be even worse than the factory setting. As explained before, it's better than nothing, but reproducible results can be only obtained with a correctly calibrated system. In this example Eye-One Match3 is used. An easy to use interface is guiding through the procedure. In a first step the used display type has to be selected. LCD, CRT or Laptop. In a next step, White Point, Gamma Value and Luminance are adjusted. For all settings the software is proposing default values that can be modified, if needed.

The measurement itself is simple: A "mouse-like" little device, connected to the USB port of the computer is measuring a defined color array on the monitor in use. Like this the software can easily create a conversion table defining how a certain color should look like and how it actually appears.

With the measuring head in place the actual measurement takes a few minutes. Also here, the user is guided through the needed steps: Contrast Calibration, RGB Calibration and Luminance Calibration. The last and final step is to save the profile under a meaningful name. I personally recommend to include the date in the file name, as these measurements should be repeated around once a month. All screens are aging with time, which makes the repetition a must. The software takes care about the correct saving in the foreseen system folder. Independent from the operating system, the question remains how to choose the gamma space ?

Gamma space 1.00 is the ideal setting, provides error-free editing.

Gamma space 1.25 provides, on average, the perceptually uniform coding.

Gamma space 1.40 will put enormous emphasis on the deep shadows, codes will be very dense there. This gives benefit only when using image acquire devices that have cooled CCD.

Gamma space 1.72 is the gamma space of un-calibrated Mac systems.

Gamma space 2.20 is an average between Mac and PC.

Gamma space 2.50 is the gamma space of un-calibrated PC systems.

In order to read the complete Tutorial, please visit:

http://www.fauland-photography.com/tutorial_gamma.php

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3 responses

  • Jessica Hardin

    Jessica Hardin said (22 Nov 2008):

    Good subject! I often wondered how some of my photos look to others depending on their monitor. I know how I intend for them to look as I see them on mine but that doesn't mean that everyone else will see them the same. I vote yeah for this very informative how to!

  • Peter Fauland

    Peter Fauland said (23 Nov 2008):

    Hi Jessica,
    Many people are just afraid to tackle the "difficult" subject. In fact it's not sooo tricky in the end. You are very welcome to check out the more detailed version ...

  • John Edwin May

    John Edwin May said (10 Jan 2009):

    A correctly calibrated monitor is an essential tool. I suggest purchasing Monaco OPTIX, Eye-One, or Spyder. Currently using the Monaco because that is the same one my commercial lab uses. There are many programs out there so do some investigating! I do not recommend attempting monitor calibration without the hardware / software programs. I have yet to see Apple ColorSync Utility or Adobe Gamma work at all. Novices should steer clear!

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