The Official ChromaPure thread - Page 4

Divide Y (in cd/m^2) by 3.4262591.

103 cd/m^2 ~ 30 ftL


EDIT: Tom's way is easier when using his SW.

Larry

For PC user without Excel, the free report viewer works fine:
http://www.microsoft.com/downloads/d...DisplayLang=en

My first practice session with ChromaPure was to calibrate a Sharp LC-37D5U. It went very well.
The attached .xls (zipped) shows the results. (the PDF is too large to upload) Use the free xls report viewer (see my previous post)
Now keep in mind that these old Sharp sets are a bitch to calibrate because all the grayscale controls (gains and cuts) are buried in the SM and I had no desire to attempt those at this time. So disregard the grayscale and gamma, they are atrocious.

But this TV has a 3D CMS and that is what I wanted to practice with.
You can see the results. The Chromaticity before and after in particular.

ChromaPure is so easy to use and has a simple learning curve. Many years with HCFR have educated me to the ins and outs of video calibration and Tom's guide is a real help. The ChromaPure help is also very good.

My DPT94 was bundled with MonacoXrite Pro software used many times to calibrate computer monitors. This is excellent software as well with a good work flow and is highly automated. The main components are calibrate and profile. The latter takes only 5 minutes to meter 32 patches and generates an .icm which is automatically loaded at windows boot to the video card lut. Sadly it is not well suited to TV calibration.

The Xrite bundle was puchased October 2004 so the meter is old but has been kept in a sealed bag with dessicant and seems to be in working order as far as I can ascertain.

IMO ChromaPure is well worth the investment.

 

Sharpxls.zip 455.234375k . file

Tom, why did you choose to measure brightness in the Color Decoding module but choose to measure lightness in the Color Manegement module?


Federico

Just wanted to capture both data points.

Tom,

In reading this post http://www.avsforum.com/avs-vb/showt...4#post17878314 Plasma54321 preferences are to determine the Y value by using "Bruces" calculator (url referenced earlier in the thread) and the actual measured x,y coordinates.

How does ChromaPure determine lightness when the x,y primaries are not per 709? Does it recompute a lightness value based on the measured coordinates or does it assume 709 coordinates. What are your thoughts on both methods???

Lightness is just the L in the Luv and Lab color spaces (luminance * 116 ^(1/3)-16). It is brightness that is perceptually weighted.

The issue you refer to has to do with an approach one can take to minimizing perceived color error when the display has oversaturated primaries, but no CMS to correct it (see http://www.avsforum.com/avs-vb/showp...8&postcount=44). The idea is to use the Color control to lower the luminance of the color somewhat beyond the specification to mitigate the effects of oversaturation. The 1976 dE formulas do the same thing, expect they take it too far. CIE94 and CEDE2000 are superior in this regard.

There is another issue that you may be thinking of, which is how to calculate a luminance target for non-standard primaries. ChromaPure offers that in the Options module, but the math too complicated to go into here.

Thanks for the correction.

So, do you recommend using the "Calculate Target" option when calibrating non CMS displays?

If you have no CMS, then using that option may give better results.

Yes that is basically what you state in the help file. I was wondering if you always select that for non CMS displays or if there are exceptions. I somehow don't think you try both and pick the winner.

Once you leave the safe harbor of the video standard under which the content was mastered, there will always be a certain amount of subjectivity involved. Also, if you have no CMS, then I am not sure that it matters. You have no way to adjust color luminance in any case, other than the main color control. In that case, you should use the Color Decoding module, which uses only calculated targets.

Myth No 5 did it for me, here is why:

http://www.avsforum.com/avs-vb/showp...postcount=2078

Especially this:

Will you be supporting the ColorMunki spectro?

I hadn't thought we would, but you are the second person to ask me about this, so I suppose I should take the request more seriously.

What's the advantage of this device over an i1Pro or a Chroma 5?

It's a fast spectrophotometer (plus X-Rite software) with attractive pricing from Amazon (and the usual suspects). There's been some talk about it at Calibration Forums. I can't speak to the X-Rite calibration because generic ones don't come with a report so maybe SpectraCal is doing Spyder3 style binning.

Mine tracks my C5 only dramatically faster (you can do an 11 point run in about a minute) and with negligible reading to reading/run to run variance. It does seem to read a bit high for luminance but I'm still fiddling.

Sounds reasonable. We'll add it to our roadmap.

"Myth #5: Tristimulus colorimeters, such as the Chroma 5, require special calibration tables to work well with LED-backlit LCD displays.

Fact: Not true. The claim that colorimeters, such as the Chroma 5, require special calibration to work with LED displays is an empirical assertion that stands or falls on what the evidence shows. ..."

What about the special calibration table for the i1Pro to work well with LED-backlit lcd displays? Is it really needed?

Tom, what was the reference radiometer used when testing the croma5?

Federico

Spectroradiometers, even the low-end ones, such as the i1Pro, don't have calibration tables for different display devices.

The Orb Optronics SP-100.

Not to be fractious but SpectraCal does imply they're doing something.

You'll have to ask them for specifics on what they are doing.

The i1Pro does not come with any calibration tables for specific display-types (LCD, CRT, etc.). That's the whole point of a spectroradiometer. It doesn't rely upon specially designed filters to mimic human color vision, but rather reads the spectra of light from the display directly and then uses the CIE standard observer functions to convert the spectrographic data into XYZ (and then xyY) data. This process is display-neutral and depends only on the sensitivity and resolution of the spectroradiometer.

Spectracal has stated that they make a 3X3 matrix calibration file for the C-5 instrument referenced to the LED backlight used in the current LCD displays. They say that this generic file is a one size fits all calibration that works well on all of the displays they have measured.

The use of a 3X3 matrix file typically will provide accuracy only on the display which the file was generated from. Use on displays other then the reference can provide a variety of results from ok' to unacceptable.

The calibration of the i1Pro using the LED back light as a reference light source seems to defeat the purpose of having the spectroradiometer calibrated to a full spectrum lamp which is what the device is calibrated with at the factory (integrating sphere with tungsten lamp).

All of our procedures used for adding LCD/LED support to the X-Rite meters including the i1Pro were developed with X-Rite for these very specific needs if you disagree with that then take it up with X-Rite.

Derek, you are saying that the support for the i1Pro were developed by Calman with X-Rite. As Calman, can you explain why i1Pro needs the table to work with backlight leds?

Federico

Derek,

you agreed in a previous post that you utilize the 3X3 matrix calibration methodology for the calibration to the C-5. You also outlined that you had good results and that all of the displays which you tested were essentially the same spectrally. However the fact that the instrument is referenced to a specific display means that the accuracy on a different display is dependent upon how closely that secondary display matches the piece used for the calibration file.

It does not matter who developed the routine and i have no reason to speak with the developer of the methodology. The fact that it is the only process that may be used to improve the instruments accuracy on a specific technology display for accuracy does not by itself make it accurate for all LED backlit LCD displays.

Funny since this is the method used to calibrate all tristim colorimeters even by the manufacturers themselves it is not something we invented. The matrix is a long standing method for tristim colorimeter correction.


Another interesting point and you are correct that if the LED backlights had a different spectrum then our reference LED would not work. But and a big but that is not the case I have been testing LED backlights for over a year now including the LED's themselves from the backlight manufactures and guess what they are the same.

Folks don’t let Cliff sorry “ghibliss” confuse you about how meters specifically the tristim design are calibrated. The manufacturers use reference displays and a reference spectroradiometer to create a matrix for that type of display. Now what makes this process a lot harder to do then what the average person can do is you need to find a display that can be a reference and having access to a reference spectroradiometer. The reference display needs to represent the largest number of displays in the class so the results are accurate on them. An example of this is a LCD with CCFL backlight. The CCFL design can have nearly an infinite combination of spectrums by the choice of phosphors used but the ones used for backlights all have nearly the same spectrum so we can find a LCD CCFL that represents the LCD/CCFL class and use that along with a reference spectroradiometer to create a matrix. In the end the process is very easy and only takes a few minutes what is hard is finding the reference display and maintaining it, having access to a reference spectroradiometer and a lab environment including temperature, humidly and lighting control.

The same method for creating a meter matrix is used in ChromaPure and CalMAN by using a spectro as the reference for your colorimeter you are essentially creating the same matrix a manufacturer does. The difference between this and what the manufacturers do is a reference spectroradiometer, reference display and reference lab. So using software to create a matrix is only guaranteed to be accurate for that display and meter combination.

One of these days I need to write a book on the subject.

Cliff if you wish to further debate me let's start another thread or take it offline. And leave this thread to the ChromaPure customers.

Again not be fractious but we're talking about spectros not tristims and the difference in approach between ChromaPure and SpectraCal with regard to "enhancing" spectros not the theoretical underpinnings of meter/display profiling.

Some sad news. The originator of this thread has passed away. He was a great guy and very kind to us.

http://www.avsforum.com/avs-vb/showthread.php?t=1215480

So sorry for the loss of the thread starter to the family and friends.

I have a question about the EyeOne Pro.

If possible, could you help me understand to what level you would trust a EyeOne Pro? I read in your website that you should only rely on it up till the measurement range which in this case is 0.2cd/m2.

Can I use the data from a EyeOne Pro on a Kuro to adjust gamma up till 0.2cd/m2 accurately?

Another question is, how does Chromapure adjust for low light level accuracy?

I haven't tested the i1Pro's luminance accuracy down that low. However, to measure gamma you have to go all the way down to 10% stim. Assuming 35 fL peak output and a 2.22 gamma, that means you have to measure down to 0.7 cd/m2. Although that's within its rated range, I wouldn't rely on it. If you have a Kuro Elite or KRP, put it into gamma 2 mode and test it. Is the gamma linear down to 10%? It should be.

The approach we decided to take is to recommend using the i1Pro as a reference only to create an offset and rely upon an inexpensive colorimeter (such as the Display 2) for very low light performance. Both the Display 2 and the Chroma 5 are reasonably accurate for luminance down to below 0.05 cd/m2. This is a more expensive option, but it ensures much better performance than what is obtainable with the i1Pro alone, so we believe that it is worth it.

This is a point that bears emphasizing. Although the color performance of inexpensive meters, such as the Display 2, is not as good as the i1Pro, their luminance performance is remarkably accurate down to surprisingly low levels. Furthermore, once color corrected by a known reference, they maintain their accuracy down to very low levels as well. See
http://www.avsforum.com/avs-vb/showp...&postcount=255

Thanks Tom.

Another question, if the Y readings are suspect at low light levels, how about the x,y readings. Can they be trusted on a EyeOne Pro?

Also does ChromaPure do anything to ensure that low light levels below a certain threshold are handled differently? I looked briefly, but I apologize for the next question, does it take "many readings" and average out below a certain light threshold?