I.)   Introduction and Outlook

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 look different, than photographs which are printed in the CMYK color space using an ink jet printer, professional printing machine 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 over 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 products mentioned here should be understood as recommendations - not as the holy grail! Of course, there are many other products on the market that will do the same job as good as what I am describing here.

Often a direct link is guiding you to a website where further information can be found. Commands or instructions to be clicked on or typed in the software application are indicated like this: <command>. In all practical examples given here,Adobe Photoshop CS3running under Mac OS 10.5.5 was used. The working strategy and sequence of commands is practically identical under Windows as well (although not in exact detail).

My answer to the initial question is very simple: If you want to see as much of the grey shades (or colors, of course) as possible on a computer monitor, then you need some (at least) basic calibration. Give it a try and compare before and after. For the coming parts of this tutorial, Adobe Photoshop, Version CS3 is used as an example. Where necessary, differences in other software versions are mentioned.

The color management in Photoshop 5.x.x and higher versions shows very good improvement compared to earlier versions, please do not even think of switching it off. As today probably 90% are using version CS or higher, this should not be a problem.

The calibration procedure described below will:

• accurately calibrate the system gamma
• tune the gray balance (using the Adobe Gamma (Win) or Calibrate (Mac) utility)
• enable Photoshop Color Management

II.)   The Calibration Procedure

First, in Photoshop one has to go to the <File/ColorSettings/ProfileSetup> 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.

• 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 "by eye calibration" should be fresh and well rested

III.) Software Calibration

The scale and the built-in presets of the color temperature control of CRT monitors or LCD screens is, most often, not accurate at all. The only exception are high-end color calibrated screens. To accurately set the monitor for daylight color temperature one should do the following: Position the monitor in front of a window so that both the monitor and the real-world outside daylight-scene can be seen. Turning off all interior lighting, in case not special lamps are installed, like e.g. Òdaylight lampsÓ, where the color temperature is known and matching the standard.

For practical reasons the calibration procedure under Windows and Mac OS X operating systems is handled separately here, making it easier to follow "step-by-step".

Mac OS X : Using the Display Calibrator Assistant

<System Preferences / Display / Calibrate> opens Apple's 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. Mac 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 ColorSync Utility <Applications / Utilities / ColorSync Utility>. 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.



Windows : Using the Adobe Gamma Utility

Adobe Gamma can be run directly from the <Start / Settings / Control Panel / Adobe Gamma> 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". LetÕs have a look at both of them.

Using the latter version, a clearly organized menu shows all important options and settings. On the top, there is a field for a personal description note. The rather cryptic term "Phosphors" allows to chose to monitor type (Here a look into the manual can help. Trinitron is a common choice). 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, it is recommended 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. The idea behind this concept is to help the not so trained user, so all steps are explained in detail. Please remember that the gamma 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.

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 ÒAdjusted White PointÓ is set to "Same as Hardware". ItÕs very important to tune the measuring device Ð 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.

IV.)  Hardware Calibration

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 which defines 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.

In this section the hardware calibration of the monitor (=input device) was covered. Apparently a hardware calibration of the printer-paper-ink combination (=output device) is needed as well. Please have a look at the article on Fine Art Printing, Ref.(5) for more information on this.

V.)   Chosing the right Gamma Space

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 a 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.

VI.)   Keeping the Profiles organized

Even if the described calibration procedures usually take care about the right space to save the files, it can be useful to have some idea where what is stored on the system. And let it only be to get an idea which profiles come pre-installed.
As it was explained in the beginning, ICC profiles are binary files, and are opened automatically by Photoshop, the operating system, printer drivers, etc. Profiles need to be installed in the correct location on your computer for them to be available to image editing and other applications. Depending on the operating system these locations are:

Mac OS X :

Storing profiles in /Library/ColorSync/Profiles allows all users to use them. An alternative area, for users without Admin privileges, is /Users/<username>/Library/ColorSync/Profiles - any profiles stored here are available only to the current user. The ColorSync Utility gives access to the details of individual profiles, shows gamut plots, can rename profiles, validates profile structure, among other useful tasks.

Mac OS 9.x :

For the old Mac operating system the place to look at is System Folder/ColorSync Profiles.

Windows XP and Vista :

The standard place where all profiles are stored is \Windows\system32\spool\drivers\color. Microsoft has a Control Panel Applet that emulates some of the functionality of Apple's ColorSync utility. It allows easy installation and removal of profiles, editing of internal and external names, viewing 3-D gamut plots, comparing two different profiles, and much more.

If for what reason ever the Color Applet is not used, the easiest way to install a profile in Windows XP is to right click on the profile in Windows Explorer and select "install profile". Windows copies the profile to the correct directory automatically.

Important Note : If a profile in Windows XP is replaced, the above shortcut does not work. The profiles must be manually copied to the correct directory for the original profile to be replaced.

Windows NT/2000 :

The correct system folder is \Winnt\system32\spool\drivers\color. See the above note on installing profiles in Windows XP. The same technique works in Windows 2000.

Windows 98/ME :

For those of you still using the older Windows systems, the system folders for color profiles are found here: \Windows\System\Color

VII.)  A few Checks

The test image below is very helpful to determine if the monitor black point is set correctly and to find the minimum shadow level the monitor can display. In order to get best possible results, the browser window should be set to full screen mode, as this minimizes the amount of pure white showing. The animated gif ramps the monitor output up in steps of 1 RGB unit for the very dark regime and then in steps of 2 RGB units up to RGB = (11,11,11). The starting point is pure black: RGB = (0,0,0). A top quality monitor using an excellent calibration system can show the difference between levels 0 and 1. Average monitors will not show any increase in output until level 5 to 8.

In case there is no visible difference until level 9 or 11, one of several problems can be responsible. The most common one is overly bright ambient lighting. Even with today's bright LCD screens, working under dimmed lighting is necessary for seeing shadow details. Also, monitor calibration systems are affected by ambient light to some extent. Recalibrating the display in dimmer light can solve many problems. Assuming the lighting is good, trying to calibrate the monitor to a higher black point would be the next step. The selected point may simply be too low for the screen to resolve differences in shadow levels.

One should not be surprised if the monitor can not show the darkest patches or if several successive steps appear equally bright. Only the very best - and therefore expensive - monitors that are also well calibrated will distinguish between all the patches. As mentioned above, a typical monitor in a dimly lit room will not show anything until level 5-8.

Note : The test image is an animated gif. If the web browser uses an ad-blocker that filters out animated images, one has to disable the filter or save the image in order to view in a different program. In Internet Explorer, the "Play animations in web pages" (Advanced options) setting must also be enabled.

The Monitor Luminance Sensitivity :

The next test image below helps to evaluate how well the monitor can display differences in luminance between grayscale tones. Each square in the array is split in half. The bottom half of each square has the RGB value specified at the bottom of its column. The top half of each square is darker by the offset value shown on the left edge. To make this more clear, here an example: Let's have a closer look at the bottom left square. The bottom half of the square has an RGB value (R=G=B) of 15, as indicated on the scale on the bottom. The upper half of this square is just 1 RGB unit darker, which results in an RGB value of 14. Now looking at the top left square, the upper half of the square is 10 RGB units darker than the RGB 15 value indicated on the bottom scale, resulting in an RGB value of 5. Like this, one can quickly scan across the image to determine the relative sensitivity of the monitor for the majority of the luminance scale. Taking a high-end, well calibrated LCD (Eizo CG18 e.g.), the split can be seen in all squares except the first and last squares of the bottom row, and the last square of row 2. If there is no split in any of the cells in row 2, this indicates a very poor quality monitor, bad calibration, too bright ambient lighting conditions, or a combination of these. If no split in the highlight columns (RGB Value = 239 and 255) on an LCD screen are visible, this could indicate that the display luminance is set too bright. Trying to calibrate to a luminance value of 150 cd/m? or below is worth a try. If problems resolving shadow differences, like not being able to see the split in the 5th or 6th columns (Base RGB value 79 and 95) are present this can be explained very likely by overly bright ambient lighting. The Monitor Black Point Test can help.



The image on the left side can be of some help in order to evaluate the overall monitor calibration. The first check is to ensure a good overall neutrality. The second check is a subjective evaluation of how well the calibration gamma matches with the monitor's native performance. The ideal state would be to have absolutely smooth gradients from black to white with no banding at all. A high-end monitor that is well calibrated will produce this. In most cases, unfortunately, some level of banding will be visible. By matching your calibration gamma value to your monitor, you can significantly reduce banding. This is very important for digital image editing, as it allows to distinguish imperfections in the image from calibration artifacts.

The Neutrality :

In case color crossovers are seen - alternating regions of red, green, or blue - the display calibration is broken. Trying to reset the monitor to its factory defaults and repeating the calibration procedure is the only advice to be given. If no improvement is seen, the monitor calibration system is incapable of giving good results with the monitor used. Some software packages allow building a monitor profile with a single gamma curve rather than individual curves. This can help in case of lower quality laptop or other LCD screens. Before put all the shame on the calibration system, however, it's vital to make absolutely sure the image is not viewed with a (strange) profile activated.
In case the entire gradient shows a color cast, the monitor is not calibrated adequately. Setting the controls to factory defaults, and running the calibration software again is the only thing that can be tried. If the problem persists, the calibration hardware might need repair.

Banding / Monitor Gamma :

One has to be aware, that only very few displays can show the full black to white gradient with no posterization or banding. Typically there is some banding in the shadows and in the darker mid-tone area. If the image shows banding throughout the whole range, either the calibration gamma is not well matched to the monitor's capabilities, or the monitor is simply of a lower quality.

Today, practically all modern monitors - operated either with a Mac or PC - have a native gamma near 2.2. Only a few specialized displays use other values. The traditional gamma value of 1.8 or Mac systems is a leftover from the very first monochrome Mac displays. This means that your image editing environment will benefit from changing to a gamma value near 2.2. The only drawback for Mac users is that the Mac graphical user interface elements like menus, buttons, etc. are designed for a 1.8 gamma display. These elements will appear darker with a system gamma of 2.2, but images displayed in a color managed system will have fewer display artifacts - and this is what is important at the end.

In case significant banding is visible and the calibration software allows it, increasing the gamma value by 0.1 can help. There is however some trail and error involved here. If increasing gamma creates more banding, reducing a bit should be tried. All standard monitors usually have a native gamma value of between 1.8 and 2.5.

Remark : In order to obtain the best results, the image below should be viewed without the monitor profile active. On Windows systems this is simple, as web browsers are not color managed by default. Under Mac OS X color managing of web graphics is possible. The Internet Explorer assumes untagged images like the test image below are in sRGB. So it's essential to open the file in Photoshop and assign the monitor profile in use to it. Safari on the other hand assumes images are in your monitor profile already, so no color management is applied.

VIII.)  References

Without being complete of course, here a few selected links, I consider useful in order to get deeper into the world of color management.

Ref. (1) www.eci.org - European Color Initiative
Ref. (2) www.color.org - International Color Consortium
Ref. (3) www.gretagmacbeth.com - Gretagmacbeth
Ref. (4) www.aim-dtp.net - Accurate Image Manipulation
Ref. (5) tutorial_fineartprint.php - Fine Art Printing, step by step Tutorial
Ref. (6) www.microsoft.com/resources/... - Microsoft Win XP - Color Management
Ref. (7) Color Management with Mac OS X
Ref. (8) www.apple.com/macosx/features/colorsync - Apple ColorySync