OLED Calibration Requires Special Setup Conditions

LG 55EA9800 OLED Display

LG 55EA9800 OLED Display

This is in answer to 2 queries in the Calibration Anomaly thread on the AVS Forum – www.avsforum.com – regarding the new LG OLED TVs.

Originally Posted by Pepelegal:

“If I increase the “OLED Light” from 25 to 50 then I can adjust fine the 5% with R2;G0;B-20.”  (This is after reporting horrendous amounts of green in the blacks with OLED LIght at 25 and requiring blue settings to be off the charts)

From calibrator Tom Huffman:

“These measurements were taken at the default zero values for white balance using 80% contrast and 25% OLED Light in the Expert 1 mode.”

Both of these queries use the original calibration method of keeping light levels at their midpoint during the calibration (in this case OLED Light 25).  With new display formats, this is no longer necessarily the best way to do it.  Part of the light level question has always been how to not misdirect or “slew off” the values needed in other registers with inappropriate light level content in the calibration itself.  Here’s my answer regarding OLED, seeing as how CRT was the original basic format for all of our video, and was the only game in town when Joe Kane and ISF’s Joel Silver started consumer calibrations, long before HD had hit our country:

I see no reason to use OLED Light 25 rather than 50 for your calibration. OLED is significantly different from CRT in its basic fundamentals.

With OLED there is no need to calibrate at midpoint of your light level potential, like there was with CRT.

CRT was not able to stay linear all the way up into the higher light levels. The blue gun was just not as powerful as the red and green guns were on any brand, it was just nature of the beast with CRT in general. The blue color’s light level would break down and roll off when all 3 were being pushed to their max, and as such be weaker than the red and green colors. Its Maximum Output Level was significantly lower than that of the red and green guns. We even used to defocus the blue slightly, electrostatically at the Screen pots, to get the dot size to expand a little, delivering more blue color into the dark areas, and would have to do that BEFORE calibrating, not after. Later on the guns got more powerful and we didn’t need to do that anymore, but the blue always stayed lagging behind the red and green when max’d.

As a result blue would do just fine at medium/average light levels, everything would be completely linear, but when overall light level was cranked up by maxing out the Contrast setting, the blue could never keep up with the red and green at the highest of light levels. To be able to get clean whites all the way up to 100IRE in our calibrations, during calibration we had to lower our overall light levels to midpoint of factory potential, ie. 50% Contrast. If we didn’t do this, then with User Contrast full up the resulting picture would be one with OK grayscale in the darks and mids but with dingy whites, lacking in blue. Some calibrators actually turned down the set’s overall light levels in service mode, making it impossible for the owner to crank it up too high, no matter where he set User Contrast – even 100% Contrast would not go non-linear on the grayscale. Like installing a governor on a Mustang. I am not a fan of a dim picture, so I never did that in my calibrations; but other calibrators did, as standard operating procedure.

Even if the owner wanted to use full up Contrast on his program material, we could not do our calibration at full tilt boogie or we would encounter strange colors in our grayscale patterns, like salmon colors, that try as we may could not be calibrated out and back to gray. Getting clean gray with the set cranking away at the highest of light levels was impossible, even if we did only the 20/80IRE hinge points. With CRT, calibrations absolutely had to be done at half of the set’s overall light level. Then if the owner wanted to run his Contrast full up, he would just have to live with whites that were dingy. Since scenes like that were a lot less common than most scenes, which contained mostly average light levels, those who wanted to run their Contrast full up didn’t have to deal with that dinginess all that much.

Those who didn’t mind keeping their light levels at linear operating levels – or in this case midpoint on Contrast of set’s overall light levels – had no worries and always had great grayscale after a calibration no matter what the scene. And of course the phosphors lasted a lot longer, the red and green convergence would not get “tugged on” in opposing horizontal directions by the high light levels, and the danger of screenburn happening quickly was lowered appreciably. Electrostatic focusing would change with the highest light levels, softening your picture. With CRT there were lots of very good reasons to run your contrast/light levels at the midpoint of your set’s capacity.

OLED has changed all that. OLED has no dingy whites when maxed out, it doesn’t have that anomaly of blue not keeping up with red and green at the highest of light levels, like CRT did. Convergence is a non-issue, there is no focusing at all to do, and the only remaining consideration left is LED aging and screenburn – which with OLED, while having been noticed, are just a shadow of their threat to the former format of CRT, where that threat was very high.

So there’s no reason to run your light levels at their midpoint when calibrating OLED. LG defaults them to run full up, and you may as well just play along with that for your calibration and then reduce your light levels a bit afterwards, just enough to get your WTW (whiter than white) back again. Then if you really want your set to run at 25 OLED Light, you’ll know that at least it is linear when at 50 OLED Light, which is how you have to calibrate it based on LG’s defaulting adjusting mode to 100% upon going into adjustment mode.

Most owners will want a rather high OLED Light setting like 80, very few of us are fans of a dim picture. Esp. since with OLED we can still get healthy shadow detail in our darks and crisp, transparent, beyond-inky blacks even at OLED Light 50, due to OLED’s infinite:1 contrast ratio. With OLED, that 100% light level is still linear in its grayscale.

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Robert Jones is a Professional LEVEL II ISF Calibrator. His special talent lies in using the Image Perfection protocol as the final and most crucial step in the ultrafine tuning of High-Definition Home Theater and Front and Rear Projection TV systems. He optimizes and extends the working life of Projection TVs to 20 years and beyond.  Though Bob specializes in Pioneer and Mitsubishi projection TV’s, he repairs and maintains Flat Screen and Flat Panel systems made by most manufacturers. Bob started the popular “Don’t Dump Your CRT-RPTV!” thread in 2006. It has over 13,000 posts spanning more than 400 pages and it is still going strong. These posts can be found at www.AVSForum.com  under the handle “Mr Bob”.  You can reach Bob directly at 510-278-4247 or bob@imageperfection.com.

 

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