Superior Video Quality with Easy to Use ITU Rec BR.709 HD Test Patterns
Advanced Video Techniques
~ by Ethan Harris ~
~ by Ethan Harris ~
With a simple calibration procedure your church can obtain the best video performance possible out of your video monitors, projectors, campus distribution displays and classroom TV equipment.
Video test patterns that conform to ITU Recommendation BT.709 High Definition (and ITU Rec. 2020 4K) standards are available from the AVS Forum.
It only takes a few minutes to evaluate and correct black, white, color and tint levels on each display or projector in your church. The available calibration patterns include the basic test patterns discussed in this article, as well as precision patterns that require a calorimeter for broadcast quality calibration.
The good news is that all of the AVS calibration test files are free, and there’s a manual to walk you through the calibration steps in detail.
Because most churches use consumer televisions for video displays, the basic .mp4 calibration files, or their blu-ray or .iso equivalents are all you need to get the best color and dynamic range possible from your church displays and projectors. You can use these calibration files if you lack a physical pattern generator box or calorimeter. The files will help you tune up your control room preview and program monitors with surprising accuracy too.
This article will take you through the basics of how to calibrate a typical flat screen TV that is used in many churches.
There are 4 basic test patterns that to use. These will enable you to set:
- Black Clipping
- White Clipping
- Combined Black & White Clipping
- Color & Tint
Attach a computer or laptop that can play .mp4 video to your video distribution system. In most cases the Mac or PC that feeds the church video system on Sunday will do just fine. A digital connection is preferred (HD-SDI, DVI, HDMI), as the signals reaching the display or projectors will be more accurate.
In some situations it might be easier to use a laptop and connect it directly to each display. Put the .mp4 in a loop so that it plays repeatedly while you calibrate the display.
If a TV has color temperature presets, or presets for movie, sports, news or other modes, you should set all of the displays to the same color temperature or setting. In general, although not compliant with broadcast standards, people tend to prefer brighter screens and hotter color temperatures. If you are a purist and your TV supports it, use the “broadcast” mode for more accuracy. If your stage lighting is 3200K and the display has a 3200K setting, then use this. If you use CTB (color temperature correction) filters in your lighting system, and the TV sets have adjustable temperature settings, then go ahead and do your best to match them up.
BLACK CLIPPING CALIBRATION
Click on the Image above to play the Black Clipping.mp4 file.
This calibration file is designed to eliminate (or minimize) black clipping so the display can deliver the blackest black it is capable of.
Most TV’s use the “Brightness” control to adjust the display response to black video signals
With this pattern, adjust the brightness setting to the lowest setting and display as many flashing vertical bars as possible on the solid black background.
The flashing bars should be fainter on the left and brighter on the right. Adjust the brightness control to where only bars 17 through 25 flash. The idea is to prevent bars 2 through 16 from flashing, as flashing in this area indicates clipping. Bar 16 is the “Reference Black.” Adjust the brightness control setting until the faintest flashing of bar 16 barely disappears. You may need to squint or change your viewing angle on some screens to be certain the flashing has stopped and is not visible on bar 16.
WHITE CLIPPING CALIBRATION
Click on the Image above to play the White Clipping.mp4 file.
The adjustment that controls a display’s response to white is usually called “contrast” or “picture.”
With this pattern, start by setting the white-level very low so you can easily see all or many of the flashing bars. Then turn up the “contrast” or “picture” setting on the TV and watch the rightmost bars stop flashing as you increase the white-level.
Ideally, bars 230-234 should always flash with no other bars flashing.
On some displays bars 235-253 may not completely disappear even using the highest setting. Every TV is different, and less expensive TVs might not excel with this pattern, so just do your best.
Bar 253 is the “Reference White.” If the TV is capable of it, tweak the setting until the faintest hint of flashing disappears from this bar. The white clipping description in the AVS manual goes into further
detail, and discusses other aspects that are related to white-level, such as color shift.
APL CLIPPING CALIBRATION
Click on the Image above to play the APL Clipping.mp4 file.
APL clipping test combines the back and white clipping tests into one test. It pushes your electronics by displaying full white and full black signals simultaneously.
This combination test is important because in some TV sets there are interactions between the black and white settings due to circuit design or power supply compromises.
After you have performed the black and white calibrations,
You can use the APL Clipping test to tweak the display settings to get the best balance of simultaneous black and white signals.
COLOR & TINT CALIBRATION
Click on the Image above to play the Flashing Color Bars.mp4 file.
This last test pattern will allow you to adjust the color and tint.
You will need a Roscolux #382 “Congo Blue” theatrical to perform this test. Broadcast professionals use a Wratten #2 filter, but these are hard to find and are expensive.
Some broadcast monitors have a “blue switch” that enables you to make calibration adjustments without a gel.
The Roscolux #382 is reasonably comparable to the Wratten filter, and will perform quite well for practical purposes. If you do not have this gel in your church’s collection of lighting gets, get a Roscolux gel swatch pack from your local lighting supply house. They are usually free or available for a few dollars. The swatch book contains this gel, and the small swatch is just large enough to look through with one eye as you calibrate the TV.
Look through the filter and adjust the “color” control to find a setting where the flashing boxes labelled “color” most closely match the vertical areas immediately surrounding the blinking boxes. If the TV is
of good quality the flashing boxes will seem to disappear and blend into the surrounding area. Then adjust the TV “tint” control and match the boxes labelled “tint. to the area immediately surrounding the tint flashing boxes. Again if you have a good TV display, the flashing tint boxes will also seem to disappear, and you will have 4 nearly identical vertical areas where the blinking boxes are almost invisible. You may need to adjust the color and tint settings a couple of times if the settings interact. But it shouldn’t take long to dial things in.
When you have completed these basic calibrations your displays will be at their best in terms of overall video quality. Even broadcast grade monitors will benefit from periodic calibration. Overall, colors will
be more accurate and have good saturation, and you will have blacker blacks and whiter whites without clipping.
If your church is about to purchase some new retail TV equipment, bring these files on a USB drive to your favorite retail outlet. If they will let you, plug the drive into the TV USB port and see how well the
equipment you are considering does with these test patterns. To the degree the church budget permits it, opt for the best quality image. My experience is that LED equipment often does better than LCD equipment, but let your eyes be the judge. You can use these procedures and test files on computer monitors and laptop screens too, so long as they have adjustable video controls.
After calibrating all of your displays using this simple set of standard test patterns, your congregation will be able to see better, and benefit from higher quality video during your worship services.
Ethan Harris is an accomplished top-10 market technical director with decades of pro-audio, acoustics, lighting, video, and high-tech management experience. He can be contacted at firstname.lastname@example.org