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Author Topic: i1 Profiler monitor QA odd results ?  (Read 4442 times)
Rhossydd
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« Reply #20 on: April 04, 2011, 01:25:05 PM »
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I agree with gromit and the ruler analogy. Without a higher grade, known reference instrument, you can’t possibility known how well the i1 did in measuring the colors.
So where does the i1 pro fit in the range of absolute accuracy for measuring colour ?
Presumably there's data in existence as to how good they absolutely can be, how consistent they are from reading to reading, how much they vary from sample to sample and how they're likely to change over their lifetime.
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digitaldog
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« Reply #21 on: April 04, 2011, 01:28:59 PM »
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So where does the i1 pro fit in the range of absolute accuracy for measuring colour ?
Presumably there's data in existence as to how good they absolutely can be, how consistent they are from reading to reading, how much they vary from sample to sample and how they're likely to change over their lifetime.

That’s an impossible question to answer. Compared to a $20K spectroradiometer? Compared to other devices in its price range? Which colors within color space? And its not just the instrument that’s a factor here. Its the software and entire process of calibration and profiling that makes validation using one instrument for the process less than effective.
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Andrew Rodney
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Rhossydd
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« Reply #22 on: April 04, 2011, 01:50:03 PM »
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That’s an impossible question to answer.
No it isn't.
Just in the same way you can compare your ruler to a known standard, you can get it to measure a known colour.

Maybe a 20k instrument might be accurate to 0.01 DE and consistent to 0.005 from measurement to measurement and only drift no more than 0.2DE in two years. That might be necessary for industrial process control.
On teh other hand, i1 Pros might only get accurate to 0.6 DE*, accurate to within 0.15DE from reading to reading* and drift about 1DE over two years, that migth still be a valuable standard if you were trying to see how accurate a colleague's laptop display had been calibrated or how a print has faded in daylight.

This data must be known, even if it isn't in the public domain.
We might be pleasantly surprised if we knew the facts.

* these numbers would fit the data I've collected from my own i1 Pros
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digitaldog
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« Reply #23 on: April 04, 2011, 01:59:10 PM »
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No it isn't.
Just in the same way you can compare your ruler to a known standard, you can get it to measure a known colour.

The standard hasn’t been defined. Nor the method for analyzing colors through the display system and profile (for validation).

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Maybe a 20k instrument might be accurate to 0.01 DE and consistent to 0.005 from measurement to measurement and only drift no more than 0.2DE in two years.


For what colors? All?

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This data must be known, even if it isn't in the public domain.

Such data is usually specified. You can find some data for the EyeOne Pro. Does your instrument produce this? For all colors one might measure? That’s not defined.
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Measurement geometry: 45°/0° ring illumination optics, DIN 5033
Light source: Gas filled tungsten (Type A)
Physical filters: No or UV cut (Filters not exchangeable)
Inter-instrument agreement: Average DE*94 0.4, max. DE*94 1.0 (Deviation from X-Rite manufacturing standard at 23°C for single measurement mode on 12 BCRA tiles (D50,2°)
Short-term repeatability: DE*94 <= 0.1 (D50,2°), with respect to the mean CIELab value of 10 measurements every 3 seconds on white
Data format: Spectral radiance (mW/nm/m2 /sr); Luminance Y (cd/m2)
Measurement range: 0.2 ... 300 cd/m2
Short-term repeatability: x,y: +/- 0.002 typical (CRT 5000°K, 80 cd/m2)
« Last Edit: April 04, 2011, 02:02:07 PM by digitaldog » Logged

Andrew Rodney
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Rhossydd
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« Reply #24 on: April 04, 2011, 02:52:41 PM »
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The standard hasn’t been defined.
? not sure what you mean by this. There's enough standards around in colour science to work to. It just has to be stated.
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For what colors? All?
You can just specify a range for which any standards chosen to apply, eg a known colourspace like ColormatchRGB . Just like saying a car speedometer might be accurate to +/- 2mph from 20mph to 80mph
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Such data is usually specified. You can find some data for the EyeOne Pro. Does your instrument produce this?
See you can find these sort of things out...................... in minutes ;-)
Actually my i1s might fall slightly outside that criteria. I'm seeing a higher error rate with the older spectro, not surprising seeing it's nine years old and hasn't been back to X-Rite for re-calibration. The newer one is pretty close to that spec, but without access to the same reference samples it would be bold to make too many claims for it.
What is apparent is that error rates are rarely going to exceed visible tolerances. So using them for real world verification should be acceptable.
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digitaldog
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« Reply #25 on: April 04, 2011, 02:57:10 PM »
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? not sure what you mean by this. There's enough standards around in colour science to work to. It just has to be stated.

Go ahead.

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Just like saying a car speedometer might be accurate to +/- 2mph from 20mph to 80mph

So you believe that a Spectrophotometer, and a car, have the same degree of accuracy over the same span (in your example, its the same from 20-80,mph?).

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Actually my i1s might fall slightly outside that criteria. I'm seeing a higher error rate with the older spectro, not surprising seeing it's nine years old and hasn't been back to X-Rite for re-calibration.


A procedure that some recommend once a year....

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The newer one is pretty close to that spec

You got that data how?

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but without access to the same reference samples it would be bold to make too many claims for it.

Indeed.
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Andrew Rodney
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Rhossydd
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« Reply #26 on: April 04, 2011, 03:21:05 PM »
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Go ahead.
I'm not the expert here. I'm just saying that it ought to be possible.
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So you believe that a Spectrophotometer, and a car, have the same degree of accuracy over the same span (in your example, its the same from 20-80,mph?).
It's perfectly possible to say over what range of speed a speedometer will work to a specified accuracy. Why can't a similarly appropriate set of variability over a known range be specified for a spectro ?
You can insert any other form of measuring device and variable, It's what the science of measurement is based on.
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A procedure that some recommend once a year....
Yes, it's not ideal, but I'm pretty certain that not many owners make the investment in annual re-calibration of their i1. The clue was that when I asked X-Rite they didn't immediately know how much it would cost or how long it would take, rather a give away that they're not dealing with that service very frequently.
It would be fascinating to know how the ones they do re-calibrate have drifted over time and if they still meet the criteria you've quoted, I wonder if they check ?
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You got that data how?
Consistency of readings can be done by repeatedly measuring the same targets and comparing the results. I've done it a few times when I've been interested enough and had some spare time.
i1 to i1 is harder as I've only access to two instruments, but again doing a similar test to above you can start to get a rough idea of what's going on.
I'm not defending it as definitive data, but it's more than I've read of anyone else doing.
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gromit
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« Reply #27 on: April 04, 2011, 04:31:43 PM »
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What is apparent is that error rates are rarely going to exceed visible tolerances. So using them for real world verification should be acceptable.

Try this. Create an image the width of the screen at 100% with the same gamma you're calibrating to and fill with a gradient from black to white. Hold down the shift key to ensure the fill is horizontal. (Bill Atkinson's "LAB Grays Test Image" and "Grays Test Image" are excellent for this purpose, if you can find them.)

Now calibrate and profile with your i1Pro. Look at the image above and make an assessment of how smooth the ramp is, how neutral through the range it is. (You may want to turn off Open GL as this has a tendency to screw things up.) Now calibrate/profile to identical target settings with MultiProfiler and examine the ramp again. Are there differences? Which is better? Could it be that, for neutrals at least, the eye is more discerning than the instrument/process you place so much faith in? Doing a test like this will answer these questions for yourself.
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Rhossydd
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« Reply #28 on: April 05, 2011, 02:51:46 AM »
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Try this..... make an assessment of how smooth the ramp is
Been there done that, but that's testing a different parameter of monitor performance. It doesn't tell you if colour is accurate.

Do you not see that colour accuracy might be important to some users ?
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gromit
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« Reply #29 on: April 05, 2011, 03:04:16 AM »
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Been there done that, but that's testing a different parameter of monitor performance. It doesn't tell you if colour is accurate.

As expounded above, neither will your i1. The gray ramp is just one of a number of tests to run. Personally, I've found negligible difference in colours between MultiProfiler and the best hardware calibration I can do.
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Rhossydd
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« Reply #30 on: April 05, 2011, 03:15:33 AM »
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As expounded above, neither will your i1.
No, the previous discussion has just highlighted that it's possible that an i1 may not give absolute accuracy. However it's also possible it will give give extremely accurate results and, if performing to it's manufactured specification, ought to be more accurate in colour assessment than the human eye.

You might not value anything more than your own display 'looking' right and maybe matching your prints, but others will benefit from being able to make objective comparisons of display colour accuracy. Being able to accurately measure the output of a display can, over time, can also help detect deteriorations in the output quality that wouldn't be noticed by eye alone.
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digitaldog
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« Reply #31 on: April 05, 2011, 09:09:16 AM »
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Being able to accurately measure the output of a display can, over time, can also help detect deteriorations in the output quality that wouldn't be noticed by eye alone.

That’s trending, a useful function some products provide (and again assume the instrument is consistent in delivering its data). An inaccurate but consistent instrument can provide trending to the user. Trending doesn’t tell us anything about accuracy, that’s a different metric.
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Andrew Rodney
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gromit
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« Reply #32 on: April 05, 2011, 06:04:40 PM »
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However it's also possible it will give give extremely accurate results and, if performing to it's manufactured specification, ought to be more accurate in colour assessment than the human eye.

Photography/printmaking is a visual medium, not a branch of number theory like you/many here seem to think. If the results look good and you didn't waste any/much paper getting there, where's the harm in this? People obsess too much about accuracy, numbers, gamut volume etc, with typical soulless results. You'd be better off developing your visual skills (which will immediately tell you if something is amiss) rather than treating the whole exercise as a science project.
« Last Edit: April 05, 2011, 06:23:49 PM by gromit » Logged
Rhossydd
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« Reply #33 on: April 06, 2011, 04:02:04 AM »
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Photography/printmaking is a visual medium, not a branch of number theory like you/many here seem to think.
If you won't understand that part of photography and print making, and in particular it's process control, relies on the ability to measure and replicate results why bother reading forums on the science of photography ?
You've added nothing of value to this thread. Don't waste our bandwidth.
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gromit
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« Reply #34 on: April 06, 2011, 06:35:08 AM »
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If you won't understand that part of photography and print making, and in particular it's process control, relies on the ability to measure and replicate results why bother reading forums on the science of photography ?

You just need to get things into perspective. Colour management is a tool, not an end in itself. The only reason I contributed to this thread was to correct your understanding of what monitor validation is, and its shortcomings, something you still seem to be struggling with.
« Last Edit: April 06, 2011, 06:57:35 AM by gromit » Logged
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