X-Rite EyeOne Pro / I1 Pro Recertification Now Available from SpectraCal! - Page 6 - AVS Forum
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post #151 of 156 Old 03-15-2014, 01:25 AM
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Originally Posted by gwgill View Post

Why do you assume this is a guess ? Rather than guessing yourself, how about doing a little research (ie. try googling "2 10 degree standard observer") before sowing more confusion.

1) Because I'm pretty sure I've seen the "specification" in question written as +/- 0.002(ish) x,y at D50, 80cd/m^2 ... *somewhere* ... probably on the original i1Pro information pages at x-rite-dot-com a/o the old GMB site. smile.gif

2) I was momentarily confused by the similar "syntax" to the above on the certification paper.

3) Thanks to the good folks here at AVS, the "confusion" was cleared up quite quickly.

4) Unlike some others around here, I'm willing to admit a mistake and even correct it if necessary.

5) I did do some "googlin'" (aka research) but came up empty ... by which time Mr. Iron Mike had confirmed Ted's original post.

6) Given the direction of recent "discussions" here, I wasn't emotionally willing to take Ted's post at face value without independent confirmation. Plus, I had that "false memory" thing going. smile.gif

7) As a DIY'er who is only interested in the practical application, I have never delved into the minutia of *how* dE is calculated much less the differences between the half dozen or so dE formulas ... or why we apparently need half a dozen or so dE formulas. All I really *need* to know to calibrate my display is to make the dang number as small as possible without "crossing the (RGB) streams" or screwing up the EOTF in the process. smile.gif

8) It's the Internet, these things happen, I apologize for my confusion re: (D50, 2°). Get over it. Move on. smile.gif
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post #152 of 156 Old 03-15-2014, 02:47 AM
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PS: Back to the original discussion ... sort of. And this is just me thinking out loud ... so apologies in advance ... skip if you wish. smile.gif

I "suspect" the reason that no one has tried to put an actual number on "the" absolute accuracy of the i1Pro in emissive mode is pretty simple. It's an almost impossible problem to solve (reliably) except in the case of the "reference" monitor under "reference" conditions vs "the" reference spectro. Which we've already established is no guarantee of performance in "the real world."

Conversely, in reflective mode, the characteristics of the i1Pro's lamp is well known as well as the characteristics of the calibration tile. Although i suspect (again) the lamp may eventually vary over time. Still, enough variables are known to be able to make a reasonable estimate.

Given that *every* i1Pro is (or was) checked against the reference display and spectro (and presumably had it's dE "adjusted to zero" in the process ) before it left the factory, why shouldn't we expect it to be able to track that reference spectro (or another one that traces back to it) almost perfectly under replicated reference conditions .... at least at the reference points that were used in the initial adjustment? To me then, it seems perfectly logical to get one's i1Pro back from "re-certification" with super-low dE numbers. Unless, of course, it was treated badly or had some kind of spontaneous failure. Perhaps I'm missing an elephant somewhere, but I just don't see how these "super low" dE results vs. reference is evidence of anything other than the i1Pro in question is apparently still functioning as designed/expected. wink.gif

In any case, to me, this i1Pro vs. CS-2000 a/o Jeti 1211 premise is a bit of a false choice and always has been. The real dilemma is i1Pro vs "Value added Colorimeters," and even that isn't so much a choice between either/or ... it's a question of when will you find you need more "confidence" than a table based colorimeter alone can provide. Then you have the decision of whether the i1Pro will be "good enough" or will you need to make the quantum leap to Jeti + levels. That's roughly a $9000 or more decision. So .... probably pretty easy choice(s) for the DIY'er ... and the "Professional" alike.

So in short, you either *need* a Spectro ... or you don't. .... If you *need* a Spectro then you either need 5nm (or better) accuracy ... or you don't ... and there's only one way to be sure you get it if you need it. wink.gif Simple, No? smile.gif

I really don't get all the angst, sturm und drang (and hours wasted on the internet) over this. smile.gif
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post #153 of 156 Old 03-16-2014, 06:32 PM
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Originally Posted by HDTVChallenged View Post

I "suspect" the reason that no one has tried to put an actual number on "the" absolute accuracy of the i1Pro in emissive mode is pretty simple. It's an almost impossible problem to solve (reliably) except in the case of the "reference" monitor under "reference" conditions vs "the" reference spectro. Which we've already established is no guarantee of performance in "the real world."
It is a fair criticism that X-Rite's specification for the i1pro appear to have no absolute tolerance specifications, only inter-instrument agreement and repeatability.
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Conversely, in reflective mode, the characteristics of the i1Pro's lamp is well known as well as the characteristics of the calibration tile. Although i suspect (again) the lamp may eventually vary over time. Still, enough variables are known to be able to make a reasonable estimate.
The reflective specifications are not that impressive - a white tile is the least demanding of it's linearity, wavelength accuracy or absolute spectral accuracy.
Lamp aging within it's expected lifetime is not typically an issue for reflective measurement, since it is nulled out by the calibration process. Aging or degradation of the white reference may be a more pertinent issue. [ I have seen some interesting changes in a lamps thermal response with more extreme age, that can lessen accuracy though.]
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Given that *every* i1Pro is (or was) checked against the reference display and spectro (and presumably had it's dE "adjusted to zero" in the process ) before it left the factory,
Why do you say that ? Do you have specific knowledge of the i1pro calibration process ?

I don't actually know of a mechanism for "adjusting its dE to zero", since it is a spectrometer, not a colorimeter. Yes, you convert a spectrum to an XYZ, but the accuracy of the latter is not a simple function of the accuracy of the former. Typically spectrometers are calibrated for linearity of the sensor with regard to light level, wavelength calibration and spectral level calibration. Something like the i1pro2 also has a stray light calibration table to account for cross contamination of a particular wavelengths readings by other wavelengths of light, but from the contents of this table I conclude that it is a very general correction, not created per i1pro2 instance.

My suspicion is that any attempt to tweak the the main emissive calibration curve to improve the dE accuracy for a particular display would have a negative effect on the spectral accuracy when measuring other light sources, which is not a desirable thing in a general purpose spectral instrument.
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why shouldn't we expect it to be able to track that reference spectro (or another one that traces back to it) almost perfectly under replicated reference conditions .... at least at the reference points that were used in the initial adjustment?
These are spectrometers, not colorimeters. There is more going on here than delta E when measuring displays.
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post #154 of 156 Old 03-17-2014, 12:09 AM
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Why do you say that ? Do you have specific knowledge of the i1pro calibration process ?

No. But if you're going to go through the trouble of "verifying" it against a reference, why not spend a couple of more minutes to "tweak" the spectral data. No, I don't know if they bother or if they just slap all the parts together and "hope for the best." Yet in theory, the integration routines could be tweaked, and so could the actual raw sensor data. In short, I don't see any reason that the i1Pro couldn't be tweaked. Furthermore, numerical integration isn't really all that hard, and since you *can* access the raw spectral data, I also find it odd that no one has ever attempted to "profile" i1Pros at the spectral level in software. (Yes, I realize that kind of negates the point of having a spectro. ) smile.gif It *is* my understanding that x-rite *can* take a i1Pro that doesn't meet "standards" and "adjust" or "repair" it so that it does meet "standards." Hence my logically derived assumption that it could be done before it leaves the factory.

But you bring up some other interesting points that I've been ruminating upon. I think it's relatively safe to assume that the diffraction grating and sensor array alone probably functions equally well/accurately in both reflective and emissive modes ... within a given luminance range of course. So my "thinking" is that the i1Pros are probably at least as accurate in emissive mode as in reflective within that luminance range on whatever display they are used as a reference, other displays, perhaps not so much. wink.gif Of course, your mileage may vary on anything that's *not* the reference display. Hence, why I said it's probably an almost impossible problem to state a *reliable* "absolute" emissive accuracy specification ... and indeed, for the same reasons, it might be a game of wack-a-mole to "fix" the accuracy for the reference monitor. Furthermore, imagine what would happen if x-rite were to say something like 2dE94 "max" deviation from whatever instrument and some motivated internet denizen took a random reading, under random conditions and got a result that was 2.5 dE off. biggrin.gif

In any case, it's probably worth noting that I'm sure the i1Pro was *originally* envisioned primarily as a tool for "reflective" targets (print media,et al.) as opposed to a monitor calibration device. At the time the i1Pro made it's first appearance, CRTs still ruled the landscape, particularly as computer monitors. Colorimeters were at least "adequate" for monitor profiling but totally useless for print . So, it also wouldn't surprise me that X-Rite and GMB before, would have concentrated on reflective "specs" and just say, 'Oh, yeah you can use it to profile monitors too.' wink.gif

All that being said, In 2014, choosing a monitor/display calibration measuring instrument is less of an accuracy issue and more of an economic issue. The fact remains that if you don't want to spend at least $9000 on a spectrophotometer/radiometer you have only *one* choice: (unless you want to try the ColorMunki Photo.) So again, all of the angst over i1Pro accuracy is a ... wee ... bit ... pointless. It is what it is. smile.gif

Tangentially Related Editorial Opinion Follows:

Honestly, at this point, I don't see any self-respecting professional calibrator going the i1Pro route. If you are going to charge me for a service, you had best demonstrate that you are committed to getting the most accuracy out of my display and that means you'd probably better have at least Jeti or something of similar (or better) quality in your tool box. OTOH, having *only* a colorimeter (even a nifty $6000 one) is a non-starter (for me.)

I'm just trying to keep things in perspective here. Remember, I'm a dinosaur from the age when optical-comparators were state-of-the-art and D65 +/-500°K was "good enough." wink.gif
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post #155 of 156 Old 03-17-2014, 01:23 AM
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No. But if you're going to go through the trouble of "verifying" it against a reference, why not spend a couple of more minutes to "tweak" the spectral data.
Who are you referring to ? SpectraCal have stated that they verify against their own reference derived from sampling a number of i1pro's. They admit they don't have the capability to recalibrate the instrument itself (ie. they don't know how to set the spectral calibration tables stored in the instruments EEprom, or are not prepared to do a full calibration.)

As for X-Rite, well I think you have things in reverse order. During manufacture the instrument will be calibrated using various test jigs and standard sources so as to be capable of return accurate spectral readings, and then there would typically be a QA verification step at the end.
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No, I don't know if they bother or if they just slap all the parts together and "hope for the best."
Do you really think anything like that happens for an instrument sold for around $1000 ? As I've already mentioned, there are several per unit calibration tables in the i1pro, and the i1pro2 has a few more. They certainly don't just "hope for the best."
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Yet in theory, the integration routines could be tweaked, and so could the actual raw sensor data.
You can't tweak the integration routines - they are set by CIE standards. By definition you can't tweak raw sensor data - that's what's meant by "raw". If you have the knowledge and the reference equipment, an i1pro can certainly be recalibrated by re-creating the spectral calibration tables. That's what happens when you send it back to X-Rite for recalibration.
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In short, I don't see any reason that the i1Pro couldn't be tweaked. Furthermore, numerical integration isn't really all that hard, and since you *can* access the raw spectral data,
Spectral data isn't raw - it's been converted from the raw sensor values by the driver using the spectral calibration tables stored in each instruments EEProm.
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I also find it odd that no one has ever attempted to "profile" i1Pros at the spectral level in software. smile.gif It *is* my understanding that x-rite *can* take a i1Pro that doesn't meet "standards" and "adjust" or "repair" it so that it does meet "standards." Hence my logically derived assumption that it could be done before it leaves the factory.
Why do you assume this is not the case ?
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But you bring up some other interesting points that I've been ruminating upon. I think it's relatively safe to assume that the diffraction grating and sensor array alone probably functions equally well/accurately in both reflective and emissive modes ... within a given luminance range of course. So my "thinking" is that the i1Pros are probably at least as accurate in emissive mode as in reflective within that luminance range on whatever display they are used as a reference, other displays, perhaps not so much. wink.gif
That's not a safe assumption, since they are calibrated in different ways. Emissive measurement has an absolute calibration curve that's set in the factory. Typically this would be created by measuring a reference light source with the instrument and then creating a correction curve from the (wavelength calibrated) sensor reading to the known (or reference instrument measured) light source spectrum. The reflective measurement curve is actually that of the white reference (yes, each white reference is measured at the factory and the results stored in the instruments EEProm). Before doing a reflective measurement, the instrument is calibrated by measuring the white reference. So reflective measurements are probably slightly more accurate than emissive measurements. On the other hand, emissive measurements don't have to worry about FWA./OBE or the illuminant being possibly unknown.
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Of course, your mileage may vary on anything that's *not* the reference display.
*What* reference display ? There simply doesn't have to be one - this is a spectrometer, not a colorimeter!
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Hence, why I said it's probably an almost impossible problem to state a *reliable* "absolute" emissive accuracy specification ... and indeed, for the same reasons, it might be a game of wack-a-mole to "fix" the accuracy for the reference monitor. Furthermore, imagine what would happen if x-rite were to say something like 2dE94 "max" deviation from whatever instrument and some motivated internet denizen took a random reading, under random conditions and got a result that was 2.5 dE off. biggrin.gif
Typically spectral instruments refer to color specification against a standard illuminant, such as illuminant A, not a display (ie. check out the Minolta CS2000 and JETI specbos 1211). It appears that X-Rite have omitted such a specification though.
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In any case, it's probably worth noting that I'm sure the i1Pro was *originally* envisioned primarily as a tool for "reflective" targets (print media,et al.) as opposed to a monitor calibration device.
What makes you think that ? It's predecessor (the Spectrolino) also had emissive measurement capability, and there was even a display only version of the i1pro called the Eye-One Monitor.
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At the time the i1Pro made it's first appearance, CRTs still ruled the landscape, particularly as computer monitors. Colorimeters were at least "adequate" for monitor profiling but totally useless for print .
You think so ? Why don't you go and check out the DTP51, an instrument used extensively in print, by those who couldn't afford a DTP41!
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So, it also wouldn't surprise me that X-Rite and GMB before, would have concentrated on reflective "specs" and just say, 'Oh, yeah you can use it to profile monitors too.' wink.gif
There is no reason to think this, and many reasons to think the contrary.
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Honestly, at this point, I don't see any self-respecting professional calibrator going the i1Pro route. If you are going to charge me for a service, you had best demonstrate that you are committed to getting the most accuracy out of my display and that means you'd probably better have at least Jeti or something of similar (or better) quality in your tool box. OTOH, having *only* a colorimeter (even a nifty $6000 one) is a non-starter (for me.)
"Perfect is the enemy of good". So it seems that you have decided that since an i1pro isn't as perfect as a $9000 or $30000 instrument, that it's not worth using.

All I can say is that I'll pick an i1pro over any colorimeter out there when it comes to measuring a display with a spectrum that the colorimeter hasn't been calibrated for. At least I'll know it's going to be within 1-2 dE worst case, rather than 3 - 5 - 10 for some of the colorimeters out there.
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post #156 of 156 Old 03-17-2014, 09:26 AM
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Oy vey! Where to start. Clearly you've misinterpreted several points I was trying to make. Let me try to clarify:
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Originally Posted by gwgill View Post

Who are you referring to ?

XRITE and GMB before them. smile.gif
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As for X-Rite, well I think you have things in reverse order. During manufacture the instrument will be calibrated using various test jigs and standard sources so as to be capable of return accurate spectral readings, and then there would typically be a QA verification step at the end. Do you really think anything like that happens for an instrument sold for around $1000 ? As I've already mentioned, there are several per unit calibration tables in the i1pro, and the i1pro2 has a few more. They certainly don't just "hope for the best."

Exactly my point. smile.gif
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You can't tweak the integration routines - they are set by CIE standards. By definition you can't tweak raw sensor data - that's what's meant by "raw". If you have the knowledge and the reference equipment, an i1pro can certainly be recalibrated by re-creating the spectral calibration tables. That's what happens when you send it back to X-Rite for recalibration. Spectral data isn't raw - it's been converted from the raw sensor values by the driver using the spectral calibration tables stored in each instruments EEProm.
Why do you assume this is not the case ?

Again. Exactly the point I was making ... perhaps my terminology was not precise enough. smile.gif What I meant was that you'd probably want to "calibrate" the results at each spectral measurement data point ... which appears to be what you're saying above.
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That's not a safe assumption, since they are calibrated in different ways. Emissive measurement has an absolute calibration curve that's set in the factory. Typically this would be created by measuring a reference light source with the instrument and then creating a correction curve from the (wavelength calibrated) sensor reading to the known (or reference instrument measured) light source spectrum. The reflective measurement curve is actually that of the white reference (yes, each white reference is measured at the factory and the results stored in the instruments EEProm). Before doing a reflective measurement, the instrument is calibrated by measuring the white reference. So reflective measurements are probably slightly more accurate than emissive measurements. On the other hand, emissive measurements don't have to worry about FWA./OBE or the illuminant being possibly unknown.

And yet, the hardware itself is exactly the same. The only differences being the "reference target. And how the spectral data is "interpreted." My point was simply that the i1Pro lamp is probably *not* a perfect illuminant source and thus adjustments would have to be made to account for that. Which seems to be the point you're getting at above. If, therefore, you're going to make those adjustments for reflective mode, why not do the same to account for "imperfections" in the reference monitor in emissive mode. (See below.)
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*What* reference display ? There simply doesn't have to be one - this is a spectrometer, not a colorimeter!
Others have implied that both SpectralCal and X-RITE run their i1Pro calibration(s) a/o QA checks against a reference "Spectro" (specifically a CS-2000, currently) using color/white "patches" or fields displayed on a specified "reference monitor" as the reference target. If there is any mistake there, it's in the fact that I took that statement at "face value." smile.gif

Edit: The point I was trying to make in the previous post was that *if* the above statement is true, then it makes perfect sense that the i1Pro would be *most* accurate (perhaps even super-accurate) when compared to the CS-2000 while using that "specified reference monitor" to display the calibration targets, since presumably that's also how the "integration table" was originally set up (calibrated) at the factory.
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"Perfect is the enemy of good". So it seems that you have decided that since an i1pro isn't as perfect as a $9000 or $30000 instrument, that it's not worth using.

No, I'm just saying that if I already have i1Pro level accuracy, I'm not going to pay anyone to come in and calibrate my display unless they have an a significant hardware advantage over what is sitting in my closet. smile.gif

Furthermore, having a Jeti (or the like) would go a long way towards demonstrating that one is committed to the "craft" and that they aren't just trying to make a few quick bucks on the down-low with a $200 instrument that's had a few extra tables added. And while it's true, I've never been to an ISF or THX class and my eyes will glaze over when you start talking about 2° and 10° observer functions ... yada ... yada, after nearly 20 odd years of calibratin' "stuff" I'd put my actual calibratin' skills (on any one of my personal displays) up against any "pro." Hubris? ... perhaps ... but from my perspective the only thing a "pro" would possibly bring to the table is better measurement equipment. .... OTOH, if you picked a random display that I've never seen before, I might flail around for a few days until I get a handle on all it's "quirks." But that's really ok too. I have the luxury of "time," whereas a "professional" doesn't. Then again there's the question of whether the "pro" would know my display(s) as well as I do. Some of them date back to the Jurassic age. wink.gif

I call that my principle that one doesn't need to know how to solve the thermodynamic model of an internal combustion engine to be able to change said engine's spark plugs. At the end of the day, it's just lefty-loosy, righty-tighty ... but gently now, don't over-torque. wink.gif Clearly, more in-depth knowledge is required if you're designing the engine, or writing calibration software. Thankfully, at this point, I don't need to do either of those things. So, taking the time to learn all the color-science minutiae would actually be counter productive (in my case.) smile.gif
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All I can say is that I'll pick an i1pro over any colorimeter out there when it comes to measuring a display with a spectrum that the colorimeter hasn't been calibrated for. At least I'll know it's going to be within 1-2 dE worst case, rather than 3 - 5 - 10 for some of the colorimeters out there.

Clearly, I have no issues with the above statement. smile.gif

PS: Sorry for all the edits ... I'm going to have to start proof reading these novellas "offline."
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