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crt calibration

post #1 of 15
Thread Starter 

I have a number of color grading broadcast monitors. I'm having a nightmare calibrating. As you may be aware, in the broadcast industry it is normal to use blue only mode. However, when I adjust using blue only mode, I get a red which measures 37% of white. I have used smpte test patterns and confirmed results on a spectrometer.

What is going wrong? The image clearly looks too red in comparison to a domestic plasma whose red is set to 21% of white.

Any advice will be welcome.
post #2 of 15
I'm not a pro, but it sounds like you will probably have to adjust the gains and cuts of red. If you can't do it via the user menu, you will have to do it via the service menu.

I can imagine the service menu of a CRT being very dangerous if you don't know how to navigate, though.

You could also just adjust the color control until red measures correctly. I would rather have red fixed and a deficiency of blue than to have overpowering reds..
post #3 of 15
What make/model display do you have? What controls do you have?
If you only have the global Color/tint then use your meter and adjust your color control to reduce the average luminance error until you have the least difference between all 3 colors. Use the tint to reduce the Delta H errors to the lowest value across all secondary colors.
Then view content and make the final teaks. If you have Calman or Chromapure do a saturation sweep to see how the set tracks.
Edited by airscapes - 2/9/13 at 3:02pm
post #4 of 15
Thread Starter 

Sony bvm14m4e and jvc 1050pnd

Both are production broadcast monitors and should theoretically achieve somewhere close to 21% red using blue only mode. As the broadcast industry do not use meters to calibrate monitors, there is only color and phase. Broadcast monitors have precision decoders and standard phosphors.

I need to know why I cannot achive 21% red using blue only mode

post #5 of 15
They're supposed to have precision decoders, but I had a Sony PVM-1390 years ago that had strong red push. It was an NTSC 13" CRT production monitor. Looking through the colored filters from Avia, I could see that if I lined up blue, red was way too strong. Visually, skin tones had the chronic sunburnt look. I checked it with pattern generators and DVD players. I did end up dialing color in a compromise position between what was good for red and what was good for blue, but leaning more toward what was good for red.
post #6 of 15
Thread Starter 
Hmmmmmm...the worry being that we calibrate our home TVs. However, we never really see what the director see, as it is more than likely they have an incorrectly calibrated monitor

It seems standards in the films /broadcast industry have dropped
post #7 of 15
broadcast industry do not use meters to calibrate monitors
That is actually not correct - we have a lot of broadcast customers who use LightSpace CMS for monitor calibration... especially if being used for grading.

It is true that monitors used for general monitoring within the broadcast transmission operation are rarely accurately calibrated, but that's because thay are not used for critical colour monitoring, just basic signal checking.

post #8 of 15
Thread Starter 
True, Steve. However, most of the industry will use proper calibration gear initially, after that it is generally the smpte test pattern. D65 can only be achieved with correct calibration. Proper calibration does not happen enough. In the industry blue only mode is a requisition, if it hasn't got blue only mode a broadcast monitor cannot be classed as grade 1.

Generally, you will hear colorist, within the industry, talk about the blue mode/smpte as the standard calibration technique, unaware of red push, as it is assumed a broadcast monitor with standard phosphor should not exhibit such color anomalies.
post #9 of 15
Generally, you will hear colorist, within the industry, talk about the blue mode/smpte as the standard calibration technique, unaware of red push, as it is assumed a broadcast monitor with standard phosphor should not exhibit such color anomalies.

Sorry, no, that is not correct at all.
I am actually a colourist, with a lot of credits to my name, and Light Illusion provides calibration to many of the grading facilities around the world - both post-production and broadcast.
No professional colourist would ever rely on 'blue only' for calibration of a grading display.


post #10 of 15
Thread Starter 
Sorry, does seem that I genralised all colourist under the same catergory.Steve your a credit to the industry.

So, my next question is, why do we have blue only mode when you can get more accuracy eyeballing an image?
Especially when you have red push at 37% for a pro monitor, what chance had a domestic set? Dve, spears and munsil...etc, all seem to advocate the use of blue filters.
post #11 of 15
No probs - and thanks for the comment.
I really do appreciate that.

The 'blue' only mode works with displays that have fixed gamut and RGB Separation, that is intrinsically accurate.
It wont work on displays that are inaccurate as all you are doing is matching the 100% blue to the component of blue within white.
That is not accurately correcting gamut, just matching it effectively to itself.

Does that make sense?

post #12 of 15
Depending on where in the broadcast chain the monitors were being used prior to you getting them, it's possible they were calibrated to a much warmer color temperature... possibly 3200K or 5500K or 5700K. If that's the case the "21% red" standard derived from d65 calibration does not apply to those calibrations. Presumably the controls of the monitors will support calibration to d65.

The blue-filter method is really imprecise because the filters vary so much, as does the spectral distribution of the phosphors used in various displays. You could make it accurate if you had full control over the filter and phosphors, but that's rarely the case and filters do change over time and have to be replaced to avoid an inaccurate result.
post #13 of 15
Thread Starter 
The monitor is a grade 1 monitor used for colour grading. It is set for D65. It has EBU phosphors. In theory blue mode should be able to get at least 5% near to the correct target. Blue mode will never be as good as proper calibration, but should get an image which is generally good. I generally use smpte. Patterns via DVD or generator, using pal SD colour space (monitor is HD with ebu phosphors)
post #14 of 15
Thread Starter 

I'm back on this again. I have more theories. I'm beginning to think that, for crt and plasma, blue only mode is better than using a meter.it
I guess it is due to apl? I was working on a plasma with decoder controls, using the avs709 decoder test pattern, i adjusted the plasma decoder for best match of all 3 primaries. Result was the same as.blue only mode, red 37% of white. I will try using apl patterns and see the results. Taking into account blue only mode us done with full screen pattern, rather than single window patterns, this is the only explanation.
post #15 of 15
Thread Starter 
Bingo! Chad b was right. The error turned out to be excessive red push on the component inputs. Unfortunately, my dvd player with sdi output is no longer working, so had to make do calibrating via the svhs input. The results werestunning! Used blue only mode and auto color adjust, then confirmed results with meter, which showed all values spot on!
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