Determine DTP-94 white point accuracy? - AVS Forum
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post #1 of 15 Old 05-29-2012, 03:00 PM - Thread Starter
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I am trying to use HCFR and a DTP-94 colorimeter to calibrate my Panasonic PT-AE4000U projector. The PJ is being fed the test patterns from a DVDO iScan VP50Pro scaling hub.

I purchased the DTP-94 (technically an Optix XR that came with a Monaco EZcolor bundle) in 2006 to calibrate my EIZO monitor for processing digital photos. Recently I became curious if it could help calibrate my projector, and discovered that it will, and that it works with HCFR. Although I had previously been satisfied with my PJ's images calibrated by eye, I thought I would give HCFR a go for checking color and gamma accuracy.

After doing a no-light calibration of the probe (properly, I assume), I attached it to a tripod pointing at the screen a few inches away from the 80 IRE pattern. In order to get HCFR to indicate that it is reading 6500K, I have to add a LOT of red contrast in the PJ's picture settings, and subtract quite a bit of green and blue. I have to make similar adjustments to red brightness and green/blue brightness to get a 6500K reading on the 30 IRE screen. (These steps are based on the "getting started with HCFR" instructions at Curt Palme's site.) The resulting screens look nowhere near to a neutral grey, they appear to have too much red.

So I am wondering if my colorimeter has suffered some sort of "drift" since I bought it. My assumption is that the no-light calibration step is designed to compensate for this. However, curtpalme.com indicates that the probes should be periodically sent in for recalibration, so this confuses me. Does this mean they are entering some sort of new calibration matrix into the unit? Is this something a DIYer could do? Is there a simple way to test if the probe is accurately measuring white point?
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post #2 of 15 Old 05-29-2012, 03:23 PM
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Quote:
Originally Posted by morty343 View Post

So I am wondering if my colorimeter has suffered some sort of "drift" since I bought it. My assumption is that the no-light calibration step is designed to compensate for this.

The dark offset, just calibrates the sensor for its current noise floor. It's mostly there to compensate for temperature changes.

Many people have gone through various machinations to try and see if there is a good DIY method for correcting meters, but unfortunately there just isn't.

The only way you can calibrate a probe is you have data from your probe and a more accurate probe on the same display (preferably your display). With that information you can create a correction matrix.

Joel Barsotti
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post #3 of 15 Old 05-29-2012, 03:31 PM
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morty343,

Also note that the AE4000 is red deficient even with the Red Enhanced lamp.

Jason
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post #4 of 15 Old 05-29-2012, 03:48 PM - Thread Starter
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Originally Posted by DaGamePimp View Post

morty343,

Also note that the AE4000 is red deficient even with the Red Enhanced lamp.

Jason

Thanks, but after setting D65 according to HCFR, I would submit that there is far too much red in the resulting greyscale, despite the lamp's reputation. The problem seems much more due to an inaccurate colorimeter.
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post #5 of 15 Old 05-29-2012, 04:06 PM - Thread Starter
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Quote:
Originally Posted by sotti View Post

The dark offset, just calibrates the sensor for its current noise floor. It's mostly there to compensate for temperature changes.

Many people have gone through various machinations to try and see if there is a good DIY method for correcting meters, but unfortunately there just isn't.

The only way you can calibrate a probe is you have data from your probe and a more accurate probe on the same display (preferably your display). With that information you can create a correction matrix.

Thank you,

So, given what I spent for my projector, would you say it's a worthwhile investment to send my DTP-94 to curtpalme.com? It appears they will replace it with a DTP-94 Pro for $150, but it's unclear what they charge for recalibrations of older probes.

Is the new correction matrix "locked" into the probe, sort of like a firmware upgrade?
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post #6 of 15 Old 05-29-2012, 06:04 PM
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Originally Posted by morty343 View Post

Thanks, but after setting D65 according to HCFR, I would submit that there is far too much red in the resulting greyscale, despite the lamp's reputation. The problem seems much more due to an inaccurate colorimeter.

Yes your issue does sound like the colorimeter has drifted. That along with the Red issue on the AE4000 will create a mess, as you discovered (overcompensating red). I recently acquired an AE4000 and have been going through calibration on Dynamic, Color 1 and Cinema 1, you are likely to see frequent interactions from even a single tick of a single setting.

As Joel stated you'll not know with your colorimeter (or any other for that matter) just how accurate you are without a reference. Even a brand new DTP-94 Pro is not likely to be truly accurate with every display type (much like an i1D3, which is even better). The colorimeter tables can help but again the only way to increase accuracy will be to use a spectro or have it professionally calibrated.

Best of Luck,
Jason
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post #7 of 15 Old 05-29-2012, 07:09 PM
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My understanding is that the filters used by the display2 are moisture sensitive. You can extend the accurate life of the colorimeter by storing it with those silica gel packs but they still degrade over time. I wouldn't be surprised if the dtp-94 is the same. So if you got that in '96 and didn't store it in a moisture controlled environment (and probably even if you did) I would expect it to have drifted in that much time.
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post #8 of 15 Old 05-29-2012, 09:49 PM
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Quote:
Originally Posted by morty343 View Post

I am trying to use HCFR and a DTP-94 colorimeter to calibrate my Panasonic PT-AE4000U projector. The PJ is being fed the test patterns from a DVDO iScan VP50Pro scaling hub.

I purchased the DTP-94 (technically an Optix XR that came with a Monaco EZcolor bundle) in 2006 to calibrate my EIZO monitor for processing digital photos. Recently I became curious if it could help calibrate my projector, and discovered that it will, and that it works with HCFR. Although I had previously been satisfied with my PJ's images calibrated by eye, I thought I would give HCFR a go for checking color and gamma accuracy.

After doing a no-light calibration of the probe (properly, I assume), I attached it to a tripod pointing at the screen a few inches away from the 80 IRE pattern. In order to get HCFR to indicate that it is reading 6500K, I have to add a LOT of red contrast in the PJ's picture settings, and subtract quite a bit of green and blue. I have to make similar adjustments to red brightness and green/blue brightness to get a 6500K reading on the 30 IRE screen. (These steps are based on the "getting started with HCFR" instructions at Curt Palme's site.) The resulting screens look nowhere near to a neutral grey, they appear to have too much red.

So I am wondering if my colorimeter has suffered some sort of "drift" since I bought it. My assumption is that the no-light calibration step is designed to compensate for this. However, curtpalme.com indicates that the probes should be periodically sent in for recalibration, so this confuses me. Does this mean they are entering some sort of new calibration matrix into the unit? Is this something a DIYer could do? Is there a simple way to test if the probe is accurately measuring white point?

using a spectro is the only way to check your meter's accuracy on a given display
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post #9 of 15 Old 05-29-2012, 10:33 PM - Thread Starter
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Thanks all,

I contacted Tom at curtpalme.com, and he stated that they will do a recal/upgrade to the probe for $150, but given that the calibration report is software-based, they only offer support for ChromaPure. He did indicate that the numbers in the report can be used to create an (unsupported) matrix in HCFR. As I more of a DIYer and am not necessarily interested in dead-on accuracy (very close is ok), can anyone give me an idea of the steps needed to port a re-profiled probe's numbers into HCFR?
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post #10 of 15 Old 05-30-2012, 08:37 AM
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Quote:
Originally Posted by morty343 View Post

Thanks all,

I contacted Tom at curtpalme.com, and he stated that they will do a recal/upgrade to the probe for $150, but given that the calibration report is software-based, they only offer support for ChromaPure. He did indicate that the numbers in the report can be used to create an (unsupported) matrix in HCFR. As I more of a DIYer and am not necessarily interested in dead-on accuracy (very close is ok), can anyone give me an idea of the steps needed to port a re-profiled probe's numbers into HCFR?

Why not rent a spectro and create your own matrix using hcfr?

Derek

CTO / Founder - SpectraCal Inc.
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post #11 of 15 Old 05-30-2012, 09:38 AM - Thread Starter
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Why not rent a spectro and create your own matrix using hcfr?

Not knowing this was an easy option, I didn't think to consider it. Are there online vendors that rent spectrophotometers (that work with HCFR)? Or will I have to search locally? I am in the Minneapolis area.
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post #12 of 15 Old 05-30-2012, 10:08 AM
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SpectraCal has a nice rental program. See their website. I'd provide a link, but I'm posting from my phone...
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post #13 of 15 Old 05-30-2012, 11:15 AM
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Quote:
Originally Posted by morty343 View Post

Thanks all,

I contacted Tom at curtpalme.com, and he stated that they will do a recal/upgrade to the probe for $150, but given that the calibration report is software-based, they only offer support for ChromaPure. He did indicate that the numbers in the report can be used to create an (unsupported) matrix in HCFR. As I more of a DIYer and am not necessarily interested in dead-on accuracy (very close is ok), can anyone give me an idea of the steps needed to port a re-profiled probe's numbers into HCFR?

Look at the new HCFR thread. There is a spreadsheet that allows you to do this.

http://www.avsforum.com/avs-vb/showp...&postcount=658

Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
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post #14 of 15 Old 05-30-2012, 03:41 PM - Thread Starter
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Thanks all,

It's becoming clear to me (and perhaps other readers) that I have just enough knowledge of the subject to be dangerous. The guide on curtpalme.com's site is very helpful to newcomers, written to make it step-by-step easy, while not delving too deep into math/theory. Because I learn faster by trying something as I'm going along before reading an entire set of instructions, early on I decided to attach my DTP-94 onto a tripod and plug it into my laptop while toggling between the HCFR program and scrolling down the online guide. After viewing my results I realized that I may be working with a probe requiring a "correction matrix", so I started this thread.

The advice/links provided to me so far have been helpful (at a minimum, they helped me realize I was working with the outdated 2.1 version of HCFR ), and they showed me that I probably need to do some more research on the topic, such as to how to integrate probe correction numbers into HCFR, rather than continue to post questions that probably have answers on this and other sites. At the point when I think I've learned enough to make inquiries that aren't too basic, I may post back...
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post #15 of 15 Old 06-07-2012, 06:07 PM - Thread Starter
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I now have had a chance to work with HCFR quite a bit. I also decided to invest in a ColorMunki Display as I did not completely trust my DTP-94, and also because it is designed to handle projectors as well as displays and is reasonably priced. (It unfortunately won't, however, work with Eizo's earlier version of ColorNavigator supported by my CE240W PC monitor, but that is a separate issue.rolleyes.gif)

As it turns out (at least according to the results from the colormunki), the DTP-94 was probably reporting accurately. What I did not originally understand was that RGB levels can be shown to be in balance at D65, but if the gammas of the primaries are out of whack then the greyscale can still have a noticeable bias. My AE4000U is connected to a DVDO iScan VP50 Pro video hub/scaler, which can output the relevant calibration screens, including a continuous 0-255 grey ramp. It was this screen that made me think the projector was outputting too much red. The projector offers the ability to adjust the gamma of each primary on a 9-point graph (or they can all be adjusted at once on a Y graph). When I looked at the individual primary gammas in HCFR and started tweaking them in the projector, I was able to somewhat compensate for red's gamma being much lower than blue or green, but as Jason pointed out, the projector does have a red-challenged lamp and there are trade-offs. In the end what I decided was that I may just have to abandon D65 and use a slightly biased "white" point in order to get a reasonably smooth greyscale, even if it isn't perfectly neutral. For example, using D75 was easier to work with. I saw there is a recent thread dedicated to calibrating this PJ in this forum, so I'll post any other thoughts there. Thanks again to all who replied.
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