Step 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | < Previous | Next > |
Step 6 - Control Adjustment
This step instructs you how to adjust your display before making any measurements. The instructions shown are dependent on your selection in the preceding display controls screen.
Depending on your selection in the preceding display controls screen, you will see one or two buttons labeled "Make Display Black" and "Make Display White". These features are for your convenience when adjusting the brightness and contrast controls. The "Make Display Black" button will fill the display with black to make it easier to adjust the black level, or "brightness" as it is commonly called. The "Make Display White" button will fill the display with white to make it easier to adjust the picture, or "contrast" as it is commonly called. On displays that only have software controls, these features will not be very convenient or usable, but they will be handy for users with physical controls on the display.
Before you start, please recognize this is the step that is most often done incorrectly when calibrating a display, so we're going to try and describe it as clearly and concisely as we can. By properly adjusting your controls, you will maximize the contrast ratio of your display so that you can see as much information as possible in the shadows and highlights, and you will set the proper luminance (brightness or white) of the display for your ambient lighting conditions. Please note that you won't be able to make a mediocre display perfect or make the brightness high enough for all ambient viewing conditions. You will only be able to make the display as good as it can be, and you may have to alter your ambient lighting conditions to compensate for any deficiencies in your display if accuracy is very important to you.
First, give your display time to warm up.
Displays typically change in behavior as they warm up. This is usually only important for the most color-critical work, but it is an important fact to know and understand nonetheless.
Basically, the rule is simple. Don't turn on your display and immediately start calibrating. Turn it on and use it for a little while, giving it a chance to warm up and reach a stable brightness.
Second, decipher your controls.
Nearly every display has at least a single control for adjusting the picture, but many displays have two controls, one for the picture and one for the black level. While most CRTs have both controls, most modern LCDs only have the picture control. And, some displays are adjusted through software in a control panel software like those on an iMac and some displays have physical controls on the units themselves. We only point this out in case you are not familiar with your display's controls and you need to read your display's user guide to locate them.
On a cautionary note, it is possible for the control labels to be swapped on a display with both controls, but it is not very likely. However, you should take the time to determine the real functions of your controls, and if the labels are indeed swapped, make a note of which control to use when prompted by the instructions. Basically, one of the controls will affect the brightness of black on your display (a 24bit RGB 0,0,0 signal from the computer) and one will affect the brightness of white (a 24bit RGB 255,255,255 signal from the computer). You should put a picture up on the display, then turn both controls down to their minimums. Pick one control, turn it up to its max and observe the change. If the picture becomes clearly visible again without the black areas becoming overly gray, you have most likely just increased the picture/contrast control. If instead, the display turned gray all over without the picture becoming clearly visible, you have most likely just increased the black level/brightness control. We use the term "most likely" because these controls can be linked so that a major change in one can affect a noticeable change in the other, so you have to use your judgement as to which is having the greater effect on the desired outcome. On displays with a single control, the control will be a picture/contrast control.
Third, adjust the black level.
Now, if you have a black level/brightness control, the trick is to adjust the black level/brightness before you adjust the picture/contrast. Proper black level/brightness adjustment is important so that you don't lose information in the shadows of your images. If the black level/brightness adjustment is set too low, the display will show colors that you cannot distinguish from the native black of the display, which is the same black as the display appears when it is turned off. If the black level/brightness adjustment is set too high, black will appear gray and your images will look washed-out. The black level/brightness adjustment will vary based on the lighting of your viewing environment. If your display is in a dark room, the black level/brightness adjustment will be lower than if your display is in a well lit room. This is because the adjustment typically needs to be increased to overcome the flare caused by the room lighting.
In order to adjust the black level/brightness, you need to be able to distinguish between true black of the display and the black of a 24-bit RGB 0,0,0 pixel. This is typically hard on LCDs because they don't have much unused area surrounding the image area that you can compare to a black image displayed on the screen, so you just have to judge the black pixels to the unused area around the LCD edges. However, most LCDs lack a black level/brightness control so it is usually a moot point. On CRTs, there is typically an unused area around the image area (unlike television sets where the image is over-scanned and is masked by the bezel of the television chassis) that creates a clearly visible edge between itself and the image on the display. This allows you to display a black image on screen and compare its brightness to the brightness of the unused area. If you are having trouble distinguishing the unused area or it's really thin or small, you can use the vertical size control to shrink the height of the image area, or you can use the vertical center/position control to shift the image area up or down to make the unused margin area larger. When you are done adjusting the black level, you can simply resize or shift the image area back to where it was.
Again, if you have a black level/brightness control, use the "Make Display Black" feature or put a black image up on-screen. Then, raise the black level/brightness control until you can see a difference between the image area and the unused area, then lower the control until the difference goes away. At very low resolutions, you should be able to see "raster lines" or "scan lines" in the image area, but at higher resolutions, the image area will just appear to be a solid patch of gray. Realize that some displays (especially older CRTs) have hardware flaws that may never allow the black level/brightness to be raised enough. Also, on some displays, you may never be able to lower the black level/brightness enough. The ambient light level also has a significant effect on the black level/brightness, so if you are in a very brightly lit environment, you may not be able to raise it enough. Conversely, if you are in a very dark environment, you may not be able to lower it enough. Just do the best you can given the limitations or your hardware and environment.
If you have trouble adjusting the black level:
Some displays will not display raster lines or a gray image area with the picture/contrast turned all of the way down and the black level/brightness all of the way up. In this case, you will need to adjust both controls simultaneously using a reference image that has both black and white in it so that you can judge both black level and white level at the same time. The best image to use for this is one with a wide border of black around its perimeter and a sufficiently large patch of white in the middle. Currently, SuperCal does not have such a helper image (like the "Make White" and "Make Black" buttons), but you can use a desktop pattern or Adobe Photoshop to make such an image for adjustment. Remember, you don't need to make display adjustments while running SuperCal. SuperCal simply provides the instructions and helper screens as a convenience.
Using the black and white image, you should set the black level/brightness at maximum and begin adjusting the picture/contrast upward until either white is at a comfortable level or black begins to become distinguishable from the unused area surrounding the image area. If you reach a point where white is bright enough and you still can't distinguish between the black in the image and the black in the over-scan area, then you're done. In this scenario, your display simply does not have enough range in the brightness control to overcome the ambient light level.
But, it is most likely that the black will become distinguishable first, so when it does, turn the black level/brightness back down until the two become indistinguishable. This is the little game that you now have to play. Repeatedly, adjust picture/contrast up and black level/brightness down until white is a comfortable level and the black area and surrounding over-scan area are indistinguishable. This is the point where the black level is set properly for your ambient lighting and the contrast is set properly for a nice, comfortable viewing brightness.
Fourth, adjust the picture.
After you have adjusted the black level/brightness, use the "Make Display White" feature or put up a white image up on-screen. Then, adjust the picture/contrast control until the brightness of white is at a comfortable level. If you are doing work for print, this should be the brightness of a clean sheet of white paper under normal viewing conditions.
For more information on display adjustment, we highly recommend reading Brightness and Contrast Controls by Charles Poynton. It is an excellent description of the principles behind picture and black level adjustment and should be read by anyone adjusting a display device such as a computer monitor or television video monitor.
Lastly, and only if your display has a color temperature control, adjust it now instead of using the White Balance adjustment in Step 9.
Some displays have a hardware setting that can vary the color temperature of white on the display. This setting has various names and could be called color temperature, white temperature, white balance or color bias. If your display has such a control, this is the proper time to use it instead of using the White Balance adjustment available in Step 9. By using your display's color bias adjustment instead of the software adjustment available in SuperCal, you will insure that your display maintains the maximum possible brightness and you will eliminate the chance of any posterization occurring because of an overly compressed gamma table in your video card. It is always best to do as much adjustment as possible in hardware before you turn to software to correct the display. Once you adjust the display's color bias settings, you may ignore Step 9 because it would be redundant (unless you do not have enough adjustment in hardware and need to supplement it with the software adjustment).
If you do not have a white balance, white temperature or color bias adjustment on your display, you should proceed with the calibration and use the white balance adjustment in Step 9 instead.