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Monitor Calibration with Adobe Gamma

The below calibration procedure will accurately calibrate the system gamma of any CRT monitor as well as the whitepoint and the gray balance. Note that the Windows NT operating system does not allow the Adobe Gamma to write to the look-up-table (LOT) in the display driver card. This is not a problem of Win95 and Win98 operating systems however some very old display driver cards do not have the writable LUT so in this case also the Adobe Gamma can not calibrate the monitor.

Finally some old versions of display driver software are incompatible with AdobeGamma (updating to he latest version will recover from this). If you do not see the “Desired Gamma” input box in Adobe Gamma utility then you have some of the above problem. General, what does the AdobeGamma do and how does it affect to the system AdobeGamma partly gathers information about the monitor and partly affects to the color appearance that is shown on the monitor and writes the monitor profile (a. k. a system profile or device profile) for the CRT monitor that characterizes that condition.

The Brightness and Contrast calibration patch This CGI patch is meant for calibrating the blackpoint of the monitor using the Brightness control knob on the monitor device. However the patches have an error and this method is not at all accurate for blackpoint calibration. Very accurate method for calibrating the blackpoint is explained below in step 4. The Selection of Phosphors Here AdobeGamma asks what is the phosphor-set that the monitor hardware has. It only writes this info into the profile (to be used by Photoshop and other color managed software), AdobeGamma does not simulate or emulate another color-space on the monitor.

Gamma Patches/Sliders and the Desired Gamma Input Box Photoshop shows either the gray gamma calibration patch or the red, green and blue amma calibration patches with the associated sliders. In addition it shows the Desired Gamma input box. This section will affect to the colors show on the monitor and to the gray balance so that the system will have the transfer-function that is specified in the desired gamma input box after the gamma match is properly adjusted using the sliders. AdobeGamma affects to the display colors by changing the look up table conversion ramp in the display driver card. Note that Macintosh Default in reality is 1. 2 and Windows default in reality is 2. 50. The gamma calibrations patches are rather limited, far more comprehensive gamma charts are rovided below in step 3. The Whitepoint Hardware -dropdown: Here AdobeGamma asks what is the actual whitepoint of the monitor hardware. This hardware whitepoint nas to be either accurately adjusted using the controls that the monitor hardware provides or it has to be measured. Adjusted -dropdown: With this dropdown AdobeGamma changes the whitepoint of the system, it does this by calculating the required change into the look up tables in the display driver card.

This option is using the hardware whitepoint information as the base for calculation so any error in hardware whitepoint is reflected to this. The Adjusted -dropdown can change the displayed whitepoint of a monitor that has been accurately set by hardware. After you have calibrated the whitepoint accurately to 6500K I strongly recommend that you experiment with this option, open the AdobeGamma and change the Adjusted -dropdown from “Same as Hardware” to 5000K…. pretty ugly isn’t it. Then Just press Cancel to AdobeGamma. The Measure… utton Behind the measure -button is a very coarse method of “measuring” the monitor whitepoint, it truly is very coarse, do not use it. In step 2 below a very accurate whitepoint calibration method is explained. The Calibration Procedure Step 1: Allow the Monitor to Stabilize Set up the normal room lighting that you will be working with. Make it rather dim and eliminate glare as much as is possible (set the lighting so that the monitor screen is not directly exposed to the lighting). Let the monitor to stabilize for at least 1 hour, this is very important !

Verify that your display driver card is set to 24-bit color (or true-color or 32-bit) mode. step 2: Set the Color-Temperature The scale of the color temperature control of CRT monitors as well as the built-in presets are most often not accurate at all. To accurately set the monitor to daylight olor temperature (6500K or D65) do the following: At noon 1 1 am… 2:00pm, (not in the morning and not in the evening but at noon) on a sunny day, position the monitor in front of a window so that you can see both the monitor and the outside real-world. Turn off all interior lighting.

In adobe Gamma utility: verify that Color Temperature/Hardware is set to D6500. verify that Color Temperature/AdJusted is set to “Same as Hardware”. Now on the monitor show a large (about 4×4 inch or 10x10cm) pure white (RGB=255,255,255) square area in the center of the screen on pure black background. It is absolutely andatory that there is nothing else on the screen but the pure white square RGB=255,255,255 in the center and the remaining screen area at pure black Now do the following: 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. ake a quick look, no longer than 3 seconds, at the monitor white. It it appears to nave a color-cast adjust the color temperature control(s) of your monitor. These is only a couple of second until the vision starts to adapt to the monitor white so be quick. 3. Repeat 1 and 2 until the monitor white does not appear to have a cast. tep 3: Choose the system gamma space Choose the desired system gamma space. This decision mainly affects to how the uncalibrated world (like the Web, non color-managed software etc. ) appears on your ICC color-managed system.

It also affects to how the Widows color-scheme appears, this can be adjusted in DisplayProperties. How to choose the system gamma space: Gamma space 1. 72 is the gamma space of uncalibrated Mac systems. Gamma space 2. 50 is the gamma space of uncalibrated PC systems. Using gamma space 1. 00 as the system space has the benefit of avoiding the slope-limiting issue in the on-the-fly isplay conversion in Photoshop but the drawback is that the range of the CRT is not being utilized the best possible way (and the Web appears very incorrectly in the browsers).

With well behaving ICC color-managed workflow such as the Photoshop 6. 0. x combined with AdobeGamma provides (less the slope-limiting issues) there are no technical or any other reasons to calibrate the monitor to any other space than to close to the native characteristic of the CRT monitor that is gamma 2. 5. This gives the additional benefit that the system is then in same gamma space as the vast majority f the systems on the Web are. In case you calibrate to gamma 2. 5 do use the new Color Dither Gamma Calibration Target.

Else choose the gamma calibration chart of your choice below and show it in your browser or better, have your browser to set the gamma chart 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. 2. 2 Step 4: Please now read the page adjust the Brightness and Contrast controls of the Monitor (open in a new browser window) and perform the blackpoint calibration that is explained there.

This is very important step as it establishes the correct blackpoint, accuracy depends heavily on the correct blackpoint. step 5: 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” in the Profile box. Press Next. Step 6 This is where the blackpoint of the monitor (Brightness and Contrast) was meant to be set by Adobe. However the blackpoint calibration sections in Adobe Gamma are incorrect, do not use them. Black-point was already accurately calibrated in step 4 so press next. step 7: Here the Phosphors info are set. In case you know the Phosphor chromaticity values of your monitor enter them by selecting “custom” from the Phosphors dropdown list box.

If you do not have these values then select Phosphors: Trinitron. CRT monitors ither have Phosphor-set that has the name “Trinitron” or another set that has the name “P22” (or “EBU”). They are very close to each other, Trinitron will match the monitor well in both cases. To query the chromaticities from the monitor download the free DDCtest utility, kindly provided by EnTech Taiwan, it is 137kB only and needs no installation, Just download it to a suitable directly and then run (double-click it) from there.

Note that the gamma and whitepoint information in the monitors EDID are usually way incorrect, rgb x,y chromaticities are most often correct, they should give you more accuraty in Photoshop. Please note that the phosphor-set that has the name “Trinitron” has nothing to do with one of the shadow mask technology that also has the name “Trinitron”. Press Next. step 8: Now you are about to calibrate the gamma, have the downloaded monitor calibration chart visible. Set the “desired gamma” value in Adobe Gamma utility to the gamma space you have chosen in step 3.

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 he dithering is fully averaged by the eye, this is about 1 to 2 meters away (3 to 6 feet). To start with, make large changes to gray slider in order to familiarize how it affects to the gamma chart, then with small movements try to match the gray gamma as accurately as possible.

The monitor can possibly 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 changes to the red slider in order to familiarize how it ffects 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 in the gamma chart.

Now use the red slider 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. Your vision is by now adapted rather interestingly but it does not matter at all, Just balance, as much as is possible, the reddish tint between the continuous tone portions and in the dithered portions of all the gray swatches. Do not try to make the hart “gray” using the red slider, instead try to balance the reddish tint between the continuous tone portions and in the dithered portions of all the gray swatches.

Now use the blue slider to balance as much as possible the bluish tint between the continuous tone portions and in the dithered portions of all the gray swatches. Again: your vision is by now adapted even more interestingly but it does not matter at all, just balance, as much as is possible, the bluish tint between the continuous tone chart “gray” using the blue slider, instead try to balance the bluish tint between the Repeat both the red slider and blue slider adjustments until there is no color difference between the continuous tone portions and in the dithered portions of all the gray swatches.

And then, it is possible that the gamma match is not good anymore (or anyhow). If you determine that the chart now has green difference between the continuous tone portions and in the dithered portions or that the overall gamma is still incorrect then increase/decrease the green slider a little. This will offset all 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.

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