Question about using a spectro and colorometer? - AVS Forum
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post #1 of 10 Old 02-23-2012, 07:23 PM - Thread Starter
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I understand that colorometers are faster than spectrometers, and so most calibrators profile their colorometer and then use that as their primary device. I just want to know if speed is the only reason or do spectrometers get inaccurate when reading low light readings?

The reason I ask is that I rented a Colormunki and did two TV's in my house so far. I profiled my Calman X2 Colorometer off of the Colormunki, then used the X2 for my calibration. Once I was done, I check the grayscale and color gamut with the Colormunki. First, I found out the Colormunki is not that slow - slower than the X2 at low light levels, but perfectly managable for the DIY'er. Second, the readings were very close to the same as I got from the X2, but were a little further off in the low light levels of the gray scale. I want to know whether I can just use the Colormunki and adjust the lower part of the grayscale or should I trust that part to the X2 more.

Thanks for any help.
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post #2 of 10 Old 02-23-2012, 08:19 PM
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Originally Posted by rocketlaw View Post

the readings were very close to the same as I got from the X2, but were a little further off in the low light levels of the gray scale.

You seem to hit on the exact reason.

Spectro's accuracy and speed fall of as light levels drop. The lower they are accurate the longer it takes to make a reading.

The CS-2000 in our shop takes ~4 minutes for readings down under 0.1 cd/m. This is because to maintain it's accuracy it has to lengthen exposure time. At the same light level we can get decent readings back from a X2 in 2-4 seconds.

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post #3 of 10 Old 02-25-2012, 09:19 AM
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Originally Posted by sotti View Post

You seem to hit on the exact reason.

Spectro's accuracy and speed fall of as light levels drop. The lower they are accurate the longer it takes to make a reading.

The CS-2000 in our shop takes ~4 minutes for readings down under 0.1 cd/m. This is because to maintain it's accuracy it has to lengthen exposure time. At the same light level we can get decent readings back from a X2 in 2-4 seconds.

So would it be accurate to say that the longer the spectros take, the more accurate they are at low light levels? Is there a way to tell the spectros to take more time to increase the accuracy in Calman?

Also, how would this inaccuracy manifest? If I let the spectros sample 5 to 10 times at low light, and it's readings were stable, could I rely on their accuracy? Or would it maintain high stability and precision but loose accuracy? I would think it would loose precision rather than accuracy...
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post #4 of 10 Old 02-25-2012, 09:29 AM
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Originally Posted by ZandarKoad View Post

So would it be accurate to say that the longer the spectros take, the more accurate they are at low light levels? Is there a way to tell the spectros to take more time to increase the accuracy in Calman?

Also, how would this inaccuracy manifest? If I let the spectros sample 5 to 10 times at low light, and it's readings were stable, could I rely on their accuracy? Or would it maintain high stability and precision but loose accuracy? I would think it would loose precision rather than accuracy...


You can't just turn up the exposure time, eventually you hit the limits of the hardware. The issue is the noise floor of the sensor, once things start to get really dark you have to filter the signal out from the noise.

The CS-2000 has a chilled sensor to keep the noise floor ultra low. So it can crank the exposure time up for even very dark readings.

We do have a low light handler for the i1 Pro inside CalMAN. It allows us to take additional readings at maximum exposure time and average them. I don't have numbers in front of me, but this does improve low level accuracy to some extent at the expense of time.

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post #5 of 10 Old 02-25-2012, 09:37 AM
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Originally Posted by sotti View Post

You can't just turn up the exposure time, eventually you hit the limits of the hardware. The issue is the noise floor of the sensor, once things start to get really dark you have to filter the signal out from the noise.

The CS-2000 has a chilled sensor to keep the noise floor ultra low. So it can crank the exposure time up for even very dark readings.

We do have a low light handler for the i1 Pro inside CalMAN. It allows us to take additional readings at maximum exposure time and average them. I don't have numbers in front of me, but this does improve low level accuracy to some extent at the expense of time.

Yeah, I was impressed with the precision at 10 and 20 IRE this morning on the i1pro Enhanced. But precision and stability isn't the same thing as accuracy. I don't have a better meter than the i1Pro to check with though.
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post #6 of 10 Old 11-29-2012, 02:56 PM
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Quote:
Originally Posted by sotti View Post



You can't just turn up the exposure time, eventually you hit the limits of the hardware. The issue is the noise floor of the sensor, once things start to get really dark you have to filter the signal out from the noise.


The CS-2000 has a chilled sensor to keep the noise floor ultra low. So it can crank the exposure time up for even very dark readings.


We do have a low light handler for the i1 Pro inside CalMAN. It allows us to take additional readings at maximum exposure time and average them. I don't have numbers in front of me, but this does improve low level accuracy to some extent at the expense of time.

Is the maximum exposure when using the LLH 2 seconds (max user option)?

I think what I am wondering is.... If I set the LLH on (which sets the exposure to 2 seconds, per the max user option), then if I don't change the Low Light Mode to more than the default of 2, then is it only taking one reading? since some readings can take quite a bit more than 2 seconds. Or is this just the exposure time, and many readings can be taken, but the meter has to process them all and will output the data as it translates it?

This is the explanation from the additional help file: "Low Light Mode – this setting determines how long the readings are taken, we will take as many readings as possible during this time"
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post #7 of 10 Old 11-29-2012, 03:11 PM
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Originally Posted by tbaudoin View Post

So just checking the switch in CalMAN will help improve the accuracy below xx and impact the speed or is there another setting to adjust as well?

There are 3 settings working in conjunction.
Enabaled/disabled
Threshold in cd/m: how dark you want it to switch on.
Exposure mode: how many samples you want to take when switched on.

I believe the defaults for the meter ship with it enabled with our default recommended threshold and sample size. We err on the side of accuracy, but feel free to tweak as you see fit.

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post #8 of 10 Old 11-29-2012, 03:31 PM
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Sorry Sotti, I was editing as you answered... I think you helped, but I really needed to clarify what I was trying to ask...
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post #9 of 10 Old 11-29-2012, 03:44 PM
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Originally Posted by tbaudoin View Post

Sorry Sotti, I was editing as you answered... I think you helped, but I really needed to clarify what I was trying to ask...

What meter are you specifically asking about?

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post #10 of 10 Old 11-29-2012, 03:57 PM
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Specifically the i1Pro, but willing to benefit from understanding how it impacts the K-10 and C6.
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