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Setting Up HD Monitors as a Standard Reference

The Technique: The underlying principle is to be able to adjust a HD monitor in a consistent and repeatable way to provide a standard reference, especially as the ambient light falling on the screen changes as the viewing environment changes. Having a consistent reference helps you to reliably assess the image for color rendition, lighting continuity, judging effects, exposure and so on. The human visual system is highly adaptable, and without a consistent frame of reference, almost anything can look "normal" to the unaided eye.

The Procedure: You will find the following controls to adjust the display on most monitors: PHASE, CONTRAST, BRIGHTNESS, and CHROMA. The Phase adjustment is not applicable to digital, so there is no need to concern ourselves with this particular function. Setting up a HD monitor as a standard reference, requires that you adjust these three key controls: (1) Contrast, (2) Brightness, and (3) Chroma. Here is a brief outline of the steps for adjusting a monitor, and they will be described in more detail below:

First, send SMPTE Bars from the High Definition camcorder so they display on the monitor. Or with several models, you can also generate the color bars from within the monitor itself. Then adjust:

1. CONTRAST - Use The White Field (most subjective)

2. BRIGHTNESS - Use The Black Pluge

3. CHROMA - Use The Two Outside Bars (after selecting Blue only)

When you turn on the SMPTE bars, they will look like this image above on your monitor screen. Now locate the controls for CONTRAST, BRIGHTNESS, and CHROMA (they maybe on an external remote control unit that plugs into the monitor). If you look directly below (or nearby) each of these knobs, you will usually find a corresponding two-position, push switch, probably marked "Auto" and "Manual". The "Auto" position, applies a standard reference signal, which has been set up during the alignment of the monitor by a technician i.e. Auto = Preset. And as the name suggests, the manual position allows for user adjustment of the Contrast, Brightness, and Chroma.

If the preset has been configured properly, it provides a good starting point for further adjustment. If for any reason you can't fine tune your monitor for the particular viewing conditions, then rely on the Preset value. If set up properly, they will be pretty close (especially the Contrast and the Chroma settings). If you find your settings vary greatly from the presets, then this may indicate you are mis-adjusting the monitor because you are getting too far removed from the baseline.

The Contrast is the hardest adjustment to set up by eye, as the correct level is very, very subjective. Be strongly guided by the Preset value for the Contrast, in particular. Adjusting the Brightness and Chroma by eye, is comparatively easy and precise.

(1) O.K. firstly the hardest one, adjusting the CONTRAST. You adjust this using the white box at the bottom left of the color bars screen (under the yellow, cyan vertical bars). You need to get this box (outlined here in red) to look nicely white, but not blooming too much (...I told you it was subjective). For the novice, it is probably several steps lower than what you think is the best level.Technicians set this up by using a little probe that they hold over this white box to measure its intensity. I've also been told you can set it with a spot meter ...... it needs to be set to 35 foot candles. If in doubt, leave this setting at the preset level which ought to be pretty close anyway, or at least closer than what you can achieve by eye.

(2) To adjust the BRIGHTNESS, you use what they call the Black Pluge. This is the little black box at the bottom right of the color bars screen (under the red and blue vertical bars). This box is outlined here in red. Inside the box are 3 vertical black bars, the left one is -3dB, the middle one 0dB, and the right one +3dB. So they are all hovering around your black baseline, which (remember) is always zero with digital (and not a 7.5 IRE black pedestal from the old analog days). So you adjust the Brightness control to find the precise point where the left bar (-3dB) just disappears. This means your black baseline at 0dB looks black to your eye (and not milky or crushed) in the particular ambient-light viewing conditions. This adjustment is pretty easy and precise (thank goodness). In practice, it is the Brightness that you really need to keep tweaking throughout the shooting day, as you move the monitor from from one set up to the next. The Brightness adjustment, in particular, is greatly influenced by the amount of ambient light falling on the screen.

(3) To adjust the CHROMA, you use the two outside color bars. But first you must switch the screen to black and white display, by selecting Blue only. Locate the Blue Only button on the control panel, and activate it. Switch back to color, and notice how the Blue bar has a little grey box underneath it, and the Grey bar has a little blue box underneath it. When you switch to Blue Only (or black & white) the boxes change to differing shades of grey. By adjusting the Chroma control, you can find the precise point where the upper grey bar, and the lower grey box, become precisely the same shade of grey and appear to merge together. In other words, you can't tell where the bar finishes and the box begins. At this point your chroma is set up properly. You can see how your screen should look when chroma is set properly in the image below. Switch between auto and manual with the Chroma preset button, and see how close this adjustment is. It is not unusual for your setting and the preset to be exactly the same (....so this might be an indication how well the monitor was set up before it left the rental house).

This is how your screen should look when chroma is set properly.

The SMPTE standard is based on having a viewing environment with a low-level wash of tungsten light at 3200 degrees Kelvin spilling on neutral grey surrounding the image (i.e. a wash of low-level 3200K tungsten light on the monitor case, which is manufactured as a neutral grey just for this reason and purpose). This gives your eyes something to reference to, otherwise your eyes just adapt, and anything and everything can look normal. As I mentioned above, human eyes are incredibly adaptable to a wide range of lighting conditions. For example, your eyes don't see daylight as blue, because they instantly adapt and effectively white balance themselves when you go outside. So you will swear colors, contrast and brightness are looking right by eye, but they will be hugely different from shot to shot depending on the monitor set up and viewing conditions. So the principle is to standardize the monitor viewing conditions by using the procedure described here. It is also important to try and control the amount of ambient light falling on the monitor screen, and a covered viewing tent is the best approach. And inside the tent, there should be (ideally) a 3200K wash of light as a reference for your eyes.

Copyright © Peter Gray

Peter Gray
(near Los Angeles)
P.O. Box 5132
Pine Mountain Club, CA 93222
United States of America
telephone: +1(661) 242-1234

dp@petergray.org