Digital Cinematography
Arts Col 752
 




Adjusting Black Level and Brightness

Gray scale chart -

The objective is to see all 16 levels of gray in this image.

To adjust a CRT: Set the "Contrast" to its mid-point, then adjust "Brightness" until the second to the darkest gray is distinguishable from the darkest. Next, adjust Contrast so that the white level appears clean and the neighboring gray levels are distinguishable from one another.

To adjust an LCD: Controls may vary on different models. Brightness may need to be adjusted by equally setting all 3 color levels lower. Use available adjustments on the monitor as much as possible, then use the video display driver settings for Brightness and Contrast as needed. Make sure you are viewing the LCD perpendicularly and centered with the screen, as apparent black level can shift when viewing off-axis.


PLUGE bars -

The lower right-hand corner of SMPTE color bars is intended for adjusting black level, the "PLUGE" bars (Picture Line Up Generation Equipment"). For almost all video calibration, the following PLUGE bars are used:

Near the middle of the rectangle are three vertical bars. The first (left) bar is "Super Black" or 3.5 IRE, the next (middle) is 7.5 IRE, which is to be considered "as black as video gets". The third is 11.5 IRE, is used for additional reference in setting the black level:

To use the PLUGE bars to adjust black level:
Use the same steps as the gray scale above (set Contrast to mid-point, and adjust brightness) until you cannot distinguish the super-black from the video black. Adjust brightness downward until you cannot distinguish the 11.5 IRE bar, and then adjust upward, stopping at just the point where it becomes visible



BEWARE!!
Avoid downloading and using color bars from the web! They can, and likely will, be calibrated incorrectly! You can check the levels in Photoshop by using the info window and the cursor position, the RGB levels for the 3 PLUGE bars should be:

3.5 IRE (Super Black) = 7,7,7
7.5 IRE (Video Black) = 16,16,16
11.5 IRE = 24,24,24


NOTE!! DV Video is an exception regarding black level processing! DV (miniDV, DVCAM, DVCPro) uses 0 IRE. Adobe Premiere and Apple Final Cut both generate 0 IRE based color bars, and the PLUGE bar area is different:

There is no Super Black bar because you can't go below zero in a 0-255 color space
0 IRE (DV Video Black) = 0,0,0
gray bar = 10,10,10

DV to DV editing and DV camera shooting will all retain the 0 IRE black level. Some editors working strictly in this environment may use video monitors that can adjust to the same 0 IRE black level input, but most analog video monitors are set for 7.5 IRE. Professional DV decks will have an "add setup" feature that brings 0 IRE up to 7.5 IRE for the monitor output. Adobe Premiere exhibits the same feature when viewing the built-in waveform scope, but will output 0 IRE DV video on the firewire port.

For calibrating your computer monitor, either type of color bar can do the job, but realize that the lower range of blacks are subject to variables and miscalibrations by operators when re-editing, projecting, or broadcasting your animation.

If your work is to be displayed on video, consider that important details darker than 16,16,16 (7.5 IRE) but brighter than zero is putting a lot of faith in the operators and display hardware that will be handling your work after its out of your hands.