Screen Contrast Test

How to read the steps

The top strip shows squares at gray levels 0, 4, 8, and so on up to 32, on a black background (level 0). The bottom strip shows squares from level 223 to 255 on a white background (level 255). Each square is labeled with its level. The first dark square and the last light square match their backgrounds on purpose, so they should be invisible.

1. 1

   Dim the room and open the chart full screen.

2. 2

   Count the dark squares you can see. The more of them you can tell apart from black, the more shadow detail the display keeps.

3. 3

   Count the light squares. The more of them you can tell apart from white, the more highlight detail the display keeps.

4. 4

   Adjust and look again. Change the display's brightness or contrast setting and see how the steps change.

What the result suggests

Several dark squares that look like black mean shadow detail is being lost: brightness may be set too low, or the display or graphics driver may be using a limited color range where the computer sends full range. Several light squares that merge with white mean highlights are clipping, often because contrast is set too high. Viewing angle and room light change both ends, so look straight on in a dim room.

For the tones in between, use the Gamma Test; to compare ten wider steps side by side, the Brightness Test. How to Calibrate a Monitor explains what the brightness and contrast controls actually do, and where adjusting by eye stops.

Full range and limited range

Computers usually send levels 0 to 255, called full range. Many TVs, and some monitors connected over HDMI, expect 16 to 235, called limited range. When the two do not match, black looks gray and washed out, or the darkest and brightest steps disappear. The setting is often called RGB range, HDMI black level, or dynamic range, in the display's menu or the graphics driver.