Photoshop v 4.01 (Win) Settings for Linear Intensity (or a gamma space)

The below procedure will result linear calibration for photoshop, in other words images after corrections will be linear.  So there will be no gamma compensation in the image data.

About the Photoshop by-the-book Calibration Procedures

The "Monitor Parameters, Gamma" -setting in the File/ColorSetting/MonitorSetup -dialog is not a monitor parameter at all.   

If the calibration is done according to the User Guide then the image-files that are created on Photoshop will have, after corrections,  that value of gamma compensation buried into the byte values of the image, what is put into the "Monitor Parameters, Gamma" box. The title of the box should be "Gamma compensation that is automatically buried into the Images Files".   

However the above calibration in Photoshop is not accurate. The function of the Gamma Slider in the Calibrate -dialog is to calibrate the display or better to say viewing gamma. It will do this to some degree, but there is error in the gamma strip in the Calibrate -dialog. The gamma strip is composed by 1-bit chessboard dither that does not show properly on any CRT monitor. It will always show a lower value than the 50% gray that it is meant to show, the quantity of the error can be very large, it depends on the quality of the monitor and the display driver. There is a correction factor for this buried into the calibration software of Photoshop, but it does not help much since the error can be some -30% or even more in the worst case. 

The relation of the "Monitor Gamma" value and the Gamma Slider is as follows:   
   
The Gamma Slider is meant to calibrate the viewing gamma to be 1.0 (linear).  
  
Image files will have that gamma compensation buried into the byte values that is put into the "Monitor Gamma" input box.  

If there is 1.8 in the "Monitor Gamma" input box, then the gamma that will be buried into the image data will be 1/1.8. This would work OK but there is the error described above.  
   
and   
   
The effect of the Gamma Slider is internally calculated from the "Monitor Gamma" value in such way that the value of the Gamma Slider need no adjustment if the "Monitor Gamma" value is changed. 

So the problem is the Gamma Slider because the dialog does not provide accurate calibration.

Calibrating Photoshop

Due to the internal Gamma Slider calculations there is another bug in the Calibration routines of Photoshop so that on a system that already has an unity gamma the Photoshop cannot be brought into calibration properly, a trick is available, but it will make the CMYK mode unusable. If you never print in CMYK then there is nothing to worry about. 

Method 1: In Case System Level Calibration IS in Effect

Photoshop calibration should be disabled in this case. Even if all major image manipulation applications allow the user to disable gamma correction, there is no such possibility in Photoshop, but the following settings will do the same.   
There are many other "Monitor Gamma" / Gamma Slider pairs that will have the same effect. However the below 1.1/-100 pair will generate smallest errors to the colors when doing image mode conversions.

Step 1: In File/ColorSetting/MonitorSetup -dialog enter the value 1.1 into the Monitor Gamma input-box.   
• Step 2: Press the Calibrate-button and the Calibrate-dialog opens. There move the Gamma slider so that it has the value -100. Then make sure that:

   
• the the red, green and blue triangles are set to:
• 0 (zero) for BlackPt
• 0 (zero) for Balance
• 255 for WhitePt 

 
by clicking the appropriate option buttons.   
Please note again that the above setting will make the CMYK mode useless, but it makes Photoshop linear.

Method 2: In Case of You Have NO System Level Calibration in Effect

Step 1: Download the linear monitor calibration image (by shift clicking the link) and view it in Photoshop. Set the Contrast and Brightness knobs of the monitor fully On.

(In case you want to set up a gamma space then download the respective gamma image here 1.1 1.2 1.3 1.4 1.5 1.6 1.72 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6)

Step 2: Please read this page to adjust the Brightness of the Monitor 

Step 3: Go into the File/ColorSetting/MonitorSetup -dialog, enter the value 1.0 (if you are setting a gamma space instead then enter the respective gamma value) into the Monitor Gamma input-box and press OK to exit MonitorSetup dialog, (you must exit from this dialog in order to get the change updated by Photoshop).   

Step 4:  Go back into the File/ColorSetting/MonitorSetup -dialog, move it so that it does not cover the Monitor Calibration Image, press the Calibrate-button and the Calibrate-dialog opens. There make sure that:   
   

• the the red, green and blue triangles are set to:
• 0 (zero) for BlackPt
• 0 (zero) for Balance
• 255 for WhitePt 
   
Then adjust the Gamma Slider so that the Monitor Calibration Image shows good match in all the gamma sections (ignore the gamma-swatch and -strip in the Calibrate-dialog they are not accurate by design).   

Note that you need to press the Preview-button each time after you change the Gamma Slider in order to have the Photoshop to display the changes in the image. Note also that you need to view the Monitor Calibration Image at such distance that the line dithering of the reference areas are fully averaged by the eye.   
  


Step 5: Repeat steps 3, 4 and once again step 3. 

Step 6: To remove any color cast use the BlackPt, Balance and WhitePt option buttons in the Calibrate-dialog and adjust the associated R, G and B slides until the color cast is nullified in gray swatches. NOTE that only small adjustments are needed here (say below 10 units). If it seems that larger adjustment to any of the BlackPt, Balance or WhitePt sliders then possibly the gamma slider is not properly set or the gamma image is not the correct one.

Finally verify that the gamma was not destroyed by step 6. In general only small adjustments should be needed in step 6. If it seems that large changes are needed in step 6 then there possibly is some problem. 
NOTE: the above procedure will accurately calibrate Photoshop in case of CRT monitors. It is possible that Photoshop can not be properly calibrated when a LCD or TFT display is in use (that can have very linear behavior by default), in such case use the first method.