I.)   INTRODUCTION and OUTLOOK

Do we really need this ? Non-professionals often think, that all these setups are only important for offset printing etc. 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.

Well, 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 basic calibration. Give it a try and compare before and after.


Photoshop 5.x.x, Monitor and RGB Calibration

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.

The calibration procedure described below will:
* accurately calibrate the system gamma
* tune the gray balance (using the Adobe Gamma utility)
* enable Photoshop color management

If you choose to use the native monitor gamma space then the images from Photoshop will appear the same in other (non profile driven) applications and on uncalibrated systems, without any attention to the gamma problem. The drawback is that the quality of your images suffer from the high gamma space.

Some limitations to the calibration procedure

Please note that this procedure does not work in Windows NT environment, NT does not allow the Adobe Gamma to write to the look-up-table (lut) in the display driver card. This is not a problem in Window 3.1x, Win95 and Win98 and WinXP but some very old display driver cards do not have the writable lut at all so Adobe Gamma can not calibrate the monitor when such old display driver card is in use. And finally some old versions of some display driver software are incompatible (update to the latest version). In addition your card has to be in 24-bit color or true-color mode.

If you do not see the "Desired gamma" input box in Adobe Gamma application then you have some of the above problem. In this case you can not calibrate into other gamma space than what your HW is, you can only characterize your system and the sliders do not affect on-line globally so you can not use this calibration procedure, you can only use the three color batches in the Adobe Gamma itself for characterization. After characterization (per the instructions of Adobe Gamma application you can use my gamma charts in Photoshop to verify that the calibration is correct. To do this set the gamma in the RGB setup dialog in Photoshop to match the gamma chart that you have downloaded and opened in Photoshop and see if you have got a good match.

II.)  Some historical aspects

In the past when one-input one-output workflows were common, in today's sense no color management was needed. All photographs were scanned by scanner operators in the CMYK color space, which was adjusted to the corresponding output device. This closed system today belongs in the past.

Today a multitude of input devices face a similarly large variety of output devices. Monitors, high-end drum and flat-bed scanners, desktop flat-bed scanners, slide and negative scanners, digital cameras etc. on the input device side and printers (ink jet, thermostat, piezo) with the most different types of inks, laser exposures, offset, laser copiers etc. on the output device side. The variety of different color spaces associated with this and the connected problems, to achieve optically equal colors with different devices led to the foundation of the ICC (International Colour Consortium, Ref. (2)).

The aim of this consortium, which was founded in 1993, was to attempt to create a standard, in order to be able to reproduce, represent and print colors independent of platform and system. To achieve this aim, specifications for ICC profiles were created, in order to be able to describe, with this, the color presentation of the different devices.

Finally, color management systems have to peform "just" two different tasks: They must simply find out which optical colors correspond to the RGB and CMYK values and they must keep these colors as constant as possible through the entire process.

Consequently, color management systems actually only do two things:

Specific colors are assigned to the RGB and CMYK values. With this, it is exactly known which colors will be established or represented by corresponding values.

The .ICC profile is a simple conversion table allowing the translation of the representative color values from one color space to the other.

III.)  The Calibration Procedure

First, in Photoshop go to File/ColorSettings/ProfileSetup dialog and set the all the six profile options to say "Ask when opening". Photoshop will then nag you every time you open an image that does not have a Photoshop profile (or there is a profile mismatch) but this is a nag you will truly appreciate. 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.

IV.) The Calibration Procedure
      >> Color-Temperature

The scale and the built-in presets of the color temperature control of CRT monitors is, most often, not accurate at all. To accurately set the monitor for daylight color temperature do the following: Position the monitor in front of a window so that you can see both the monitor and the real-world outside daylight-scene. Turn off all interior lighting.

In adobe Gamma utility:

Verify that both * Color Temperature/Hardware is set to D6500
* Color Temperature/Adjusted is set to "Same as Hardware"

Now show a large (about 4x4 inch or 10x10cm) pure white (RGB=255,255,255) square area in the center of the screen over pure black background on the monitor and adjust the "color temperature" control(s) of the monitor until the white of the monitor does not have a color-cast, this will take some time:

1. 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:

2. Take a quick look at the monitor white, if it appears to have a
color-cast adjust the color temperature control of your monitor.

Note that there is only a few seconds until your vision starts to
adapt to the white-point of the monitor.

Repeat 1 and 2 until the monitor white appears to be pure white. This will give you very accurately the D6500 daylight color temperature. Showing the large white square over pure black background (instead of showing full-screen white that was the earlier recommendation) has the effect of minimizing the error in the perception that is caused by the CRT case, they usually have a tint. One easy way to show the pure white square is to use Photoshop.

1. Create 100x100 pixel RGB image.
2. Fill it with white.
3. Maximize the Image window
4. Press the d-key, it sets the background/foreground colors to
    black and white.
5. Select the Paint Bucket Tool.
6. Press the Shift-key and while keeping it pressed click the border
    (not the image area) using the Paint Bucket Tool. This will set
    the border area of all image windows to the current background
    color (here black).
7. Press the Tab-key
8. Press the f-key twice.
9. If rulers are shown press Ctrl+r.
10. Use Crtl+ and Ctrl- keyboard combinations to size the square.

V.)   The Calibration Procedure
      >> Choosing the gamma space

Choose the gamma space you are going to work with. View the appropriate gamma image below in your browser (or have your browser to set the image as the background image of your desktop by right-clicking the displayed image and then selecting the 'Set as Background' from the pop-up menu).
1.0 1.25 1.4 1.72 1.8 2.0 2.2 2.5

1.0 (larger version)

How to choose the gamma space:

* Gamma space 1.0 is the ideal setting, provides error-free editing.
* Gamma space 1.25 provides, on average, the perceptually uniform coding.
* Gamma space 1.4 will put enormous emphasis on the deep shadows,
   codes will be very dense there.
   This gives benefit is only when using image acquire devices
   that have cooled CCD.
* Gamma space 1.72 is the gamma space of uncalibrated Mac systems.
* Gamma space 2.2 is an average between Mac and PC.
* Gamma space 2.5 is the gamma space of uncalibrated PC systems.

VI.)  The Calibration Procedure
      >> Adobe Gamma settings

Please read now the page adjust the Brightness and Contrast controls of the Monitor. This is very important step as it establishes the correct black-point.

Start the Adobe Gamma utility from the Control Panel, in wizard mode.

If the file name of the profile that Adobe Gamma has found is "Adobe Monitor Settings.icm" then press
Next button and go to step 4, else:

Make a note of the name of the profile, cancel the Adobe Gamma, then using the Windows Explorer go to c:/windows/system/color and remove (cut and paste elsewhere) that profile. This will discard the ready made profile, ready made profiles are not accurate.

Repeat the above until Adobe Gamma says "Adobe Monitor Settings.icm" in the Profile box.

Press Next.


This is where the black-point of the monitor (Brightness and Contrast) was meant to be set by Adobe. However the black-point calibration section in Adobe Gamma v 5.x.x has a bug, it is are largely inaccurate.

Black-point was already accurately calibrated before, so press next.


Here the phosphor infos are set. In case you know the phosphor chromaticity values of your monitor enter them by selecting "custom" from the phosphors drop down list box. If you do not have these values then select phosphors: Trinitron. Monitors are either Trinitron or P22 (they are very close to each other) so Trinitron will match the monitor well in both cases. Press Next.

VII.)  The Calibration Procedure
       >> Calibration using Adobe Gamma

Now you are about to calibrate the gamma.

Set the "desired gamma" value in Adobe Gamma utility to the gamma space you have chosen.

Check the view single gamma only check box if it was not selected already.

Now use the gray slider to get a as good gamma match as possible all over the chart, please remember that the gamma swatches 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 imbalance between the gammas of the red, green and blue guns the gamma chart will show this very easily. Next you will be correcting this gray balance. Un-check the "view single gamma only" check box.

To start with, 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 you will notice hue change in both the continuous tone portion and dithered portions of the swatches.

Then use the red slider to remove -or- to balance as much as is possible the reddish tint between the continuous tone portions and in the dithered portions of all the gray swatches.

Now use the blue slider to remove -or- balance as much as possible the bluish tint between the continuous tone portions and in the dithered portions of all the gray swatches.

Repeat both the red slider and blue slider adjustments.

Now it is possible that the gamma match is not good anymore.

If you now determine that you need to change the overall gamma then increase/decrease the green slider a little. This will offset the color balance so you need to repeat the red-slider, blue-slider then again red-slider and again blue-slider adjustment as described above.

Adjust & evaluate until accurate. It is somewhat tedious but well worth of the effort.

Press Next.

Leave the Hardware White Point at 6500K (Daylight).

Press Next.
Leave the Adjusted White Point at "Same as Hardware". Press Next.
Verify that the file name of the profile is: "Adobe Monitor Settings.icm". Press Finish and then Save buttons. The monitor calibration is now completed.


In Photoshop open the File/ColorSettings/RGB_Setup dialog.

Check the "Display using monitor compensation" check box.

Enter:
* Gamma: the value that you have chosen to be your gamma space.
* White-point: 6500K
* phosphor: Trinitron

Calibration is now done. Save this profile under unique descriptive name.

VIII.) The Calibration Procedure
       >> Gamma Spaces

Photoshop allows you to easily edit the image in an other gamma space than what the system is calibrated to by AdobeGamma. You only need to change the gamma value in the FileColorSettings/RGB_Setup dialog.

However, the Photoshop color management has a feature that is called as the slope limiting that is more like a bug. The slope limiting will cause errors into the shadows if the gamma-space of the system (Desired Gamma in Adobe Gamma -utility) is different than the Gamma value in RGB-Setup in Photoshop. Please see the slope limiting page about how to avoid slope-limiting errors.
About Gamma Spaces

As always I recommend to work in linear (gamma = 1.0) space for accurate and error free editing. Now that the profiles are in use this is even more important since there will be less gamma-space conversions so less errors due to the conversion when images are transferred to/from other profile driven applications or devices. Color space conversions are always done at linear light domain (gamma 1.0) so working in gamma 1.0 minimizes the gamma-out, gamma-in calculations in your working path.

When you use the linear (gamma 1.0) space, and the output path or device is not profile-driven (or natively linear) then you need to publish the images. E.g. the images that you upload to WWW, or those that you print to a non-profile-aware (or non-linear) printer. Publish == to apply the required compensation for the output device or path in concern, over a copy of the original image. (E.g. For Web images: Make a duplicate, apply inverse gamma 2.5 then save as jpeg.)

When you calibrate the system into gamma 1.0 then browsing will be somewhat irritating. So for a surfing session open the Adobe Gamma utility, set the Desired Gamma to 2.5 and leave the Adobe Gamma utility open, at the background. To recover just press Cancel in Adobe Gamma.

When you use Linear Calibration the default Windows Desktop will appear way too light. You can set the Windows colors in ControlPanel/Display/Appearance. Choose the "3D Objects" from the Items list-box and choose (or set it to) a darker gray, this is usually enough.

(Partially taken from Accurate Image Manipulation Ref.(4))

IX.)  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 Adobe gamma. For one person it might work pretty well, while for somebody else it might be even worse than the factory setting. And in any case, assuming I did it and you are doing it on the same system, the results will be significantly different.
The solution 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 between how a certain color should look like and how it actually appears. All screens are aging with the time. This means the procedure should be repeated from time to time. (I personally re-calibrate my screens once a month). The output is a so called monitor .icc profile, which has to be stored in a specific system folder. Using this the system is able to display the propercolors. If you need any practical advice on which system might be used, drop me a line.

In this section I was talking about hardware calibration of the monitor (=input device). 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).

X.)   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) European Color Initiative
Ref. (2) International Color Consortium
Ref. (3) Gretagmacbeth
Ref. (4) Accurate Image Manipulation
Ref. (5) Fine Art Printing, step by step
Ref. (6) Microsoft Win XP - Color Management
Ref. (7) Color Management with Mac OS X
Ref. (8) Apple ColorySync

to be continued.