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This topic comprises 2 pages: 1 2
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Topic: Color correcting
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 10-15-2017 02:27 PM
quote: Dave Macaulay
There's no point in checking corrected primaries in my opinion. If you get 0.314/0.351 for corrected white, all is as it should be.
That is wrong. If you input the wrong value or your meter hadn't sufficiently stabilized when reading it (easy to do on the USL PCA100) reading the corrected primary colors will spot the error (had it happen).
A common misconception is the belief that if you attain .314/.351 you are on the money everywhere. Color correcting is like using just the bass and treble controls to tune a room. With the white point, you also have a mid-range control too but it is nothing like tuning with several parametric or 1/3 octave EQ.
Just because you check one point doesn't mean the rest are good.
Even worse are the fools that pull the notch filter on the likes of the NC900 and "think" they color corrected it back to DCI because, after all it reads .314/.351 when they are done. That is as stupid as using bass/mid/treble controls to tune out a spike in the response at 10KHz. Yeah, you can move it but it is all relative to everything else you are moving and the spike will still be there when you are done.
For those interested in the whole color correction thing and yet more things to measure, check out the DCI spec sheet, section 8.3.4. It defines the minimum area of the triangle that the projector can reproduce. That once corrected that it should hold its white point over a wide range of stimuli too.
I do have to end this with. Remember, in the film days, you got what you got, unless you were a studio with a pile of reflectors to get what you wanted and nobody really cared in the cinema. It is great we have this new tool to be better and more uniform but there are many factors in putting on a show and getting the perfect color reproduction is just one of them. Most DCinema projectors (xenon, at least) out of the box will be more uniform from unit to unit than film projectors ever were.
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 10-16-2017 08:08 AM
In the film days, another big variable was the print itself. This was especially true in the final decade or so of the film days, when quality control in the mass production labs really deteriorated, and the sensitometry and densitometry checking was simply not done to the standard it had been a generation earlier.
I take Harold's point that having test and measuring equipment made and sold by totally separate entities to the makers and sellers of the equipment being tested is an important check and balance, but I still believe that built-in, automated color measuring would be a step forward for the industry. This shouldn't replace regular checks by a tech using an independently made and calibrated photospectrometer (in the same way that checking the integrity of the CLO sensor is part of the formal maintenance regime as laid down in the service manual), but in multiplex type houses where color calibration by a tech using a $10K Photo Research or Jeti meter isn't done very often and realistically never will be, it would be a boost to presentation quality.
There would be problems implementing it (e.g. port glass - you'd either have to do setup calibrations with the glass both removed and in place, or have the meter in the auditorium and connected by LAN to the projector), but none would be insurmountable.
Though, given that the two main factors that cause the color temperature of a projector's output to change over relatively short-term time periods - the xenon arc bulb and the reflector - will go away if the industry does convert to laser, this may end up being a solution looking for a problem. The problem certainly exists at present, though.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 10-17-2017 09:06 AM
I think another problem with putting auto color correction into projectors is how well they would do it. Barco is the only one of the DLPs that does CLO well. Somehow they are the only ones that figured out you needed a different calibration based on lens zoom and allowed one to have it read properly.
Christie is the only one that has figured out auto xenon adjustment. Barco has it but it is notoriously slow and inaccurate.
An NEC, well, even their light meter can, and often does, mislead one into a lower and less even light output!
So putting the overhead of making the color stable (at least as far as getting out of the projector) is going to be less than ideal and will vary by projector company.
And think about this. So you calibrate the projector using your $8,000 - $20,000 meter and now you are going to have something with FAR less accuracy and stability maintain that calibration? And if it isn't as accurate, then what was the point?
The Qualif people would love to sell you their magic $15,000 or so box that will measure your system each day and apply the appropriate color calibration to ensure you are always spot on. But who is going to dump that sort of cash per-screen? And if you do, don't forget about the meter recalibration costs (plus the labor to mount/unmount the system annually). And for what? Has ANYONE (outside of a studio screening) EVER had a paying customer complain about their color correction (and I don't mean a 2D/3D PCF file issue but actual you were at .318/.349 type color complaint)?
We'd be better served by getting the light levels right. People know when the image is too dark though they won't know the difference between 14fL and 13fL...by the time you get down to 8-9fL, they know it is too dark (and, hopefully, before).
I also hope that this insanity of using flat gain screens goes away. If your screen gain is above 1.3 and flat, you don't have even light. You can make something from nothing. If you don't have enough light with a matte-white screen, the solution is a projector that has more light, not to put in a gain screen. There is no magic there. A gain screen takes the light from the sides/corners and puts it in the middle and ensure that everyone gets a different hotspot. The overall light level goes DOWN with a gain screen, it is just the middle that goes up.
That said, I've come to the conclusion that with low-contrast projectors (all S2K), using a mild gain will have fewer complaints about the low contrast. It isn't that the picture suddenly got contrast, it is that you lowered the gain such that people don't see the "grey" of the S2K chip. Again, the solution is to NOT use the S2K projectors and if you are going to use them, think about the laser versions though that will remove their cost advantage of them.
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