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Step 7 - Black Level Measurement

The black level measurement step gives you brief instructions how to perform the black level measurement and allows you to begin the process. When you are ready to begin, press the "Begin Measuring" button.

If you have an LCD, you should keep your head stationary throughout the measurements.

If you are measuring an LCD on a laptop computer or have a first generation LCD for a desktop, it is important for you to keep your head stationary throughout the measurement process. Early desktop LCDs and most laptop LCDs typically have very poor off-axis response characteristics that cause the image to change dramatically in appearance when you move your head from side to side or up and down. Find your typical viewing position and hold your head stationary throughout the black level and response measurements. Do not move your head to make a pattern look different - use the supplied controls. It is impossible to overcome the off-axis response characteristics of the display, so you need to do the complete measurement from one position so that you insure uniform results. If you move, you will get variations in the measurements that will be seen as color tints in neutral grays.

Now, on to the measurements...

The black level measurement screen has a single vertical slider along the right edge that controls the brightness of the moving measurement bars. The goal is to adjust the slider until you can just no longer see the lower bar, but you can still see the upper bar.

Note that the upper bar is just a safety mechanism for you to help judge brightness and prevent dropping the brightness level too far. But most modern LCD screens have gotten so good that there's little chance that you could drop the brightness low enough to no longer see the upper bar. However, it is still very possible to drop the brightness level too far when ambient light levels are very high, or you're calibrating a projector or old CRT.

This step can be very difficult, but it is very important to get correct. Every measurement from here on is based on this black level measurement, so take the time to do it correctly. To reinforce the goal again, you want the brightness level set where you can just no longer see the lower moving bar. Using the arrow keys is a great help because you can adjust the slider to a point where you can still barely make out the lower moving bar, then use the down arrow key to nudge the setting lower, counting key taps if you must. Once you can no longer make out any movement where the bottom bar should be, you've got it. Don't go any lower than this or you will be giving SuperCal a false impression of the black level at which you can still see color.

You will need to do this for each color channel - red, green and blue. If this is fatiguing to your eyes, take a break between color channels and look away from the screen. Just make sure that you don't get up and walk around because you need to keep your head in the exact same location for each one of the black level measurements.

Now for some technical background...

The black level determines the lowest luminance value that you can see. This is important so that the calibration can compensate for the lower luminance values that you cannot see, due either to an imperfect display or the ambient lighting conditions of the environment. The darker the room you're in and hence the lower the ambient light, the lower you will need to move the black level slider. This is because when it is dark, there is less ambient light overpowering the lower luminance values and you can visually distinguish lower black level values. When it is brighter in the room, the ambient light overpowers the display and washes out the lower luminance values to the point that you can no longer visually distinguish them, so the measured black level will be higher.

When you have completed this step, the button will be renamed "Re-Measure" to indicate that the measurement has been completed.