How to use it
- Dim the room a little and open full screen.
- Black level: count how many of the 20 near black patches you can see against the pure black background.
- White level: count how many of the 20 near white patches you can see against pure white.
- Use the shadow and highlight steps to check that each level is a little different from the next.
On a well set up screen you should see all or nearly all patches at both ends. The very first patches are hard to see on some screens in a bright room, which is normal.
Full range and limited range, explained
Computers use full range: level 0 is black and 255 is white. Video and TV use limited range: black is 16 and white is 235. When the source and the screen disagree, you get one of two faults:
- Crushed blacks and clipped whites: the source sends full range but the screen expects limited. Everything from 0 to about 16 turns black and from about 235 up turns white. In this test, the first 15 or so black patches and most white patches disappear, and dark scenes lose detail.
- Washed out picture: the source sends limited range but the screen expects full. Black looks dark gray and white looks dull, and the whole picture lacks contrast.
This happens most often with a computer connected to a TV or monitor over HDMI.
How to fix it
- Make both ends match. In the graphics driver settings, look for an output range or dynamic range option (full or limited). On the TV or monitor, look for a setting called something like black level, HDMI black level, RGB range or HDMI range. Names vary by maker.
- For a computer, the usual choice is full on both. For a video player or console, the usual choice is automatic, or limited on both.
- Then fine tune brightness (which on most TVs sets the black level): raise it until the lowest patches are just visible, but stop before the black background turns gray.
- Fine tune contrast (the white level): lower it if the highest white patches merge into the background.
Picture modes with dynamic contrast or auto brightness move these levels around, so test with them off. Then check your gamma, which sets the mid tones.
Questions
What is black level?
How dark the darkest shades are and whether the ones just above black are still visible. Good black level means deep black with shadow detail still showing.
How many black patches should I see?
All or nearly all 20 on a well set up screen in a dim room. If every patch below about 16 is invisible, suspect a full versus limited range mismatch.
My blacks look gray. Why?
Either brightness is set too high, or the screen expects full range and gets limited range. On LCDs, black is never fully black because of the backlight, which is normal.
Should I use full or limited range?
Either works as long as the source and the screen use the same one. Computers usually work best with full range on both sides.
What is a white level test?
The same check at the bright end: patches from 235 to 254 on pure white. If they merge into the white, highlights are clipped and bright details like clouds and snow lose texture.