Black as Night … Setting Black in Post Production

Setting the black level in the post production studios is just like setting it for normal consumer displays.  Well, actually, it turns out not to be the case.  If you apply the same rules, the images will not turn out well for you at all.  And do we even have the test patterns to deal with this?  First things first, we have to unlearn how we did black level from all the videos and the training classes.  It is not the same.  (Well it is kind of both.)

(This article is a precursor to Calibration Video 19 as it provides the background and history to that particular segment.  It helps me to collect my thoughts on this entire process.)

I had a chance to work closely with a local post production company (and continue to do so) that has distinguished clients like HBO and ESPN.  When you went in their front door, you saw show cases full of Emmy Awards and other industry awards for their work.  (And now a THX Calibrated Video plaque too 🙂 )

They have a viewing room where a JVC projector sits shooting onto a 130″ screen.  It is fed by a Samsung BD player and their Color Grading station.  Next to the Color Grading station is a 50″ Panasonic Industrial plasma set.  Films and commercials are displayed on these two units and they must look as similar as possible.  Welcome to a studio where the monitors actually have to be made to look the same.

The problem begins with the thinking / assumption that there is no problem at all.  Calibrate the projector with the BD player and all is fine.  The films and all the demo materials play fine from both the BD and the WD Media players and look just as I expect them to look.  This gets saved in one memory area of the projector.  I called it “THX Movie” so that it would be easy to remember.

The problem is that the stuff coming out of the color grading station is not matching what was done from the BD player.  The brightness is way off.  My signal generators are outputting images that match what the blu ray player is outputting.  All our sources cannot be collectively broken.

I get a black magic box that will convert my test patterns from HDMI into HD-SDI.  This does not work well either because the patterns appear to be altered from their original form when they go through this conversion box.  Pieces of information are missing from the pluge pattern and the contrast patterns.  Full patterns with black levels starting at 0 up to 23 show only 16 to 23.  The color grading images still do not match up with this method of calibration.  Something else is going on, but it is hard to tell the company to junk their color grading equipment.  So what else can we do?

The device at the center of attention is the color grading station and how it outputs signals.  I need to see what my stuff looks like when it goes through the grading station pipeline.  That is not so easy at all.

We end up putting a series of grayscale jpegs (10-100%) and color pattern jpegs (RGBCMY) and other patterns like pluge and contrast patterns into the computer sourced from my DPG 1000/1200/1400/2000.  They are brought into the color grading set up like any film material and sent through the chain.  They write those patterns from the computer onto a disc and I put them into the blu ray player.  I correct for the pluge pattern on this test disc from the projector end and what results is an image that is still too dark when compared to the original calibration work done on the projector via the BD player and HDMI signal generators.  Where is the problem located?

Not like the Colorist understands the issues, but he did confirm that clients had mentioned that some of their material seemed to be too dark.

The answer lies in a discussion with the Colorist and having him show me how he does his work and what part of a signal he works with.  We pro-calibrators come from the consumer end of things where we deal with things like blacker than black and whiter than white.  I was trying to apply these rules into his world and this where the problem and the solutions started to appear.  His world does not deal with BTB or WTW.  His source material is just 0 to 100%.  He can increase the brightness or decrease it to whatever levels that he wants from scene to scene.  His working range is 0 to 255.  But when that range is received for broadcast television, it is compressed to fit the video range of 16-235.  He doesn’t do it, but the TV system does it during the broadcast.

So how does this help us?  It helps by making us understand that his 0% is our 16 value and that is the hardest part to wrap our minds around.

When we put a pluge pattern into the color grading pipeline, we do not adjust the brightness on the projector to only show video black and above.  (16 and higher).  The pluge pattern I used showed the gradations of gray from step 0 all the way to step 23.  How do we use this pattern to set for proper black levels?  First off, the projector was set to not show anything below black since the pattern coming out of the color grading pipeline would not contain that material.  So out comes a pluge pattern with 0 to 23 bars all visible.  How do we set this?

You can try to set it so that box 1 is just barely visible above box 0.  Turns out that actually does not quite work right.  End result is that the image is too dark.

The fix.  Observe the test pattern and increase brightness until you can still see distinct differences between boxes 1,2,3,4,5 and so forth.  When you start to lose this distinction, you are setting the brightness too low.  By doing it this way, the projector image now matched the image on the Panasonic plasma being fed by HD-SDI.  (I expect this to be much more evident when you watch the video in Part 19 – Setting Black Levels in Post Production – Subscription Required)

The output from the BD player also seemed fairly compatible with these now optimized settings for the Color Grading Station.  Typical for JVC projectors, we typically go into their HDMI settings and set it to expanded in order to show the BTB and the WTW material.  This results in the brightness being set lower to compensate.  This set up did not work for the grading station as it results in the images looking too dark.  The HDMI setting was then set to super white as this was just right.  The BTB would not be passed for the BD material, but that was okay.  The color grading signal came out just fine with this setting and it pretty much matched the BD settings.  Save this second setting as THX Work.

Now that was obvious … 😀

 

Michael Chen

Michael Chen is the only THX Video Systems Instructor in Canada, and beyond these borders, is one of just two THX Video Instructors in the entire world.  He has actively consulted with Spectracal and ChromaPure and has created numerous education videos on the calibration process with still more to come.  His Video Calibration Training Series has quickly become the most comprehensive and simple to understand learning tool on the market today.  He has also taught classes for both the ISF and Spectracal as well and is now spearheading his all new TLVEXP calibration training program. Let Michael teach you Video Calibration and add that additional income stream to your installation and integration business

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