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MONITOR CALIBRATION
(Last modified on February 19, 2009)


CALIBRATING BLACK AND WHITE POINTS

Tips by
Tom Niemann
Portland, Oregon
http://epaperpress.com/whoami/index.html

Many computer monitors come from the factory preset for an office working environment which may not be ideal for viewing and editing photographic images.

The sRGB IEC 61966-2.1 standard specifies a color temperature of 6500°. Most monitors have provisions for setting color temperature using on-screen menus. Be sure to set monitor color temperature before calibrating with Adobe Gamma or QuickGamma.

Be sure your display is configured for 24-bit color. With 16-bit color there is not enough color depth to calibrate properly. Let your monitor warm-up for at least 15 minutes before calibration.



Do the patches marked 0 and 10 in the grayscale appear to be the same? If they do then you need to calibrate your monitor black point. Do the patches marked 95 and 100 appear to be the same? If they do then you need to calibrate your monitor white point.

You can calibrate black and white points without any special software, just the monitor settings for brightness and contrast. Usually for ® Samsung SyncMaster 740N LCD monitor the brightness is about 39 and contrast is about 51. It takes just a few minutes to make these adjustments. As a reward you will view images on the web as they were designed to be viewed. If you're a web designer, or share images with others, then it's imperative that you calibrate your system to a standard. For the web or email use the sRGB standard

1. Black point calibration


You should be able to distinguish between the patches marked 0 and 10 in the above grayscale. Patch 0 should be perfectly black, matching the unscanned portion of your monitor, and patch 10 should be barely visible. In this section you will adjust monitor brightness so the black point is properly calibrated.

Adobe Gamma, and several web sites, attempt to adjust the black point with grayscale patches. However, the quality of monitor displays varies significantly, and attempting to read something out of low-valued patches is fraught with difficulties.

When the black point is properly set, an RGB value of (0,0,0) will appear as true black on your monitor. Increase the RGB value slightly and you should see a slight increase in intensity. The non-scanned area surrounding the displayed image is an ideal reference for the black point. The goal is to make display value (0,0,0) match the black of the non-scanned border.

For adjustments to be accurate you need to use consistent lighting when viewing your monitor. The black point for a brightly-lit room will be higher than a dimly-lit room. After setting room lights to your standard, minimize any on-screen applications (including your browser). If there are bright-colored icons on your desktop, move them to a folder and minimize the folder. You can easily retrieve them later. It is very important that your screen be completely black.

2. White point calibration


You should be able to distinguish between the 95% and 100% patches in the above grayscale. If they appear to be the same, then contrast is too high, and highlights are blocked. Most monitors work fine with contrast set at 100%. If you find this too bright, or highlights are blocked, decrease contrast and recalibrate the black point.

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CHECKING AND CALIBRATING MONITOR GAMMA

Getting it right, from the start

If you haven't already done so, calibrate your display before you go any further. Most monitors can do with a bit of help in showing correct colour and tonal range.

The little bit of time spent calibrating your monitor now will make matching your printer to your screen easier, and save you a lot of frustration, re-scanning and adjustment later on.

Check out your present monitor 'gamma' with the exclusive 'Gamagic' estimator. To use the estimator below, sit well back from your monitor and half close your eyes. Then look for the place where the squares lose their colour, and are most closely matched to a neutral grey tone. The number beneath that section tells you the approximate gamma of your monitor.

The "Gamagic" gamma estimator.
(You saw it here first folks!)




If the gamma of your system appears to be outside the 'norm' of 2.2, then you should adjust it.

 CALIBRATING GAMMA

If you have a full version of Adobe Photoshop ®, it comes with a little utility called Adobe Gamma ®. You can use it in conjunction with the adjusment squares, and just ignore the imprecise Adobe test patterns. In particular, Adobe's instructions for setting the brightness level lead to a very poorly defined black level. One good feature that Adobe gamma does have, is the ability to save settings, allowing you to quickly switch between gamma values, colour temperatures, etc.

On Windows ® control panel double click on Adobe Gamma ® icon to load it. Please choose a target gamma from the following list depending on your operational system *

Gamma 2.0
Gamma 1.6 Gamma 2.2
Gamma 1.8

* For PC we recommend Gamma 2.2
* For MAC we recommend Gamma 1.8


Follow Adobe Gamma instructions adjusting gamma with the new window that you has been loaded. When you finished calibrating return to this page to check out it.

If you've set up the gamma of your monitor correctly you should be able to distinguish most of the steps of this greyscale from their respective black or white backgrounds.



If not, it's back to the drawing board I'm afraid; or at least another shot at setting up the gamma. As a last resort, try winding the brightness setting of the monitor up a bit, although you shouldn't have to. A well adjusted monitor, viewed in subdued light, should reveal the left-hand greyscale down to 10 or below, and a difference in the lighter tones right up to 255.

You can also download this GIF file by right clicking over it and selecting "save image as....". Then you can use it to check out your printer's ability to render a full tonal range as well.

Finally, check out with this link to a clever Java applet by Hans Brettel.

If you are satisfied with the results save
the profile in Adobe Gamma (srgb color space profile.icm) to make it the default color space for your monitor in all your Windows ® applications.

Remember this calibration will be correct since you  don't  make new adjustments on monitor control settings, so if you do that you will need to recalibrate it.


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