RE: Comparison of 2 spectros using Delta e (Fons Put)
RE: Comparison of 2 spectros using Delta e (Fons Put)
- Subject: RE: Comparison of 2 spectros using Delta e (Fons Put)
- From: Fons Put <email@hidden>
- Date: Mon, 17 Jan 2011 14:51:07 +0100
- Acceptlanguage: nl-NL, nl-BE
- Thread-topic: Comparison of 2 spectros using Delta e (Fons Put)
Back in 2008, we carried out a study on the inter instrument agreement of spectrophotometers. You can find a summary on our website:
http://www.graphicbrain.com/studies-by-vigc/spectrophotometer-nightmare/
What could you learn? I think following conclusions could be important:
1. Each brand of spectrophotometer has it specific behaviour
2. The light source of the spectrophotometer is an important component regarding to the accuracy: for example, gas filled tungsten light is not the best choice for accurate measuring of dark violet/blue colors.
3. The white calibration patch should be in good condition to achieve a minimum accuracy.
4. Make a distinction between proces control (delta E) and visual assesment (delta E 2000 or others) to communicate color differences
Regards,
Fons Put
Senior Consultant
Flemish Innovation Centre for Graphical Communication
________________________________________
Van: colorsync-users-bounces+fons.put=email@hidden [colorsync-users-bounces+fons.put=email@hidden] namens email@hidden [email@hidden]
Verzonden: zaterdag 15 januari 2011 21:02
Aan: email@hidden
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Today's Topics:
1. Re: Comparison of 2 spectros using Delta e (Terence Wyse)
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Message: 1
Date: Fri, 14 Jan 2011 15:02:19 -0500
From: Terence Wyse <email@hidden>
Subject: Re: Comparison of 2 spectros using Delta e
To: ColorSync User List <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; CHARSET=US-ASCII
On Jan 14, 2011, at 2:02 PM, david wollmann wrote:
> Hello everybody,
>
> I've been doing an exercise here comparing two different instruments, an i1Pro and a DTP41. Both devices have the UV filter. I made a target of the it8 basic chart since I can fit all the patches in the area of an 8x10 inch print. I then printed both at the same time on some 24 inch wide fine art paper using an Epson 9800.
>
> The Delta E 94 values are
> Total - 1.63
> Best 90% - 1.50
> Worst 10% - 2.81
>
> The worst 10% are mainly in the cyans and a few light yellows and one green patch.
>
> I guess my question is what all can learn from this?
That inter-instrument agreement is an issue! It doesn't surprise me that a (former) Gretagmacbeth instrument, the EyeOne Pro, and the XRite DTP41 don't agree all that well. The "spectral head" and optics on these instruments are quite different. You'll find better agreement among Gretabmacbeth devices and among X-Rite devices....but not so much to each other.
While you said you printed them at the same time, I would make sure you read *the exact same chart*. Obviously, the DTP41 requires a special layout to be read in strip mode...so I would print the DTP41 chart, measure it, and then with the EyeOne Pro in "spot" or "patch" mode instead of strip mode, read the chart perhaps 3-5 times (in different spots within each patch obviously) and average the results and then compare that.
The other option would be to print your current charts several times in differing orientations (4 prints at 90 degree intervals) to compensate for subtle coverage/inking differences on your 9800. At the very least, print as many as you can across the 24" width and measure/average all of them. Believe it or not, patch layout makes a difference AND differences will show up across the width of the printer.
> Since this is only a comparison between two devices with no standard reference how would I determine which spectrophotometer is giving me more accurate readings?
Not easy....maybe impossible. There was a Gretagmacbeth program called NetProfiler that was an effort to resolve these disagreements but it was only designed to work with GMB SpectroEyes.
You could use a standard reference such as the "Lab Reference Card"...
http://www.printtools.org/pt/color-reference-cards/lab-reference-card
...but that's designed to be used with hand-held spectros. You could measure it using your EyeOne Pro but it's not formatted to work with the DTP41. (they do offer a 36mm patch size version but without an image or any further information, it's unclear whether it's formatted to work with the DTP41 or not).
The only way to get some sense of which spectro is more accurate, you'd need to introduce a 3rd or 4th spectro into the mix....even then, you're only going to reach a *consensus* between the different spectros, not which one is the most accurate in an absolute sense.
There's a new thing XRite came up with, XRGA, that attempts to reconcile the difference between legacy XRite and Gretagmacbeth instruments and their different calibration standards. You can find out more here:
http://www.xrite.com/product_overview.aspx?ID=1336
I haven't looked into XRGA enough to know whether it resolves inter-isntrument disagreements or not.
>
> My subjective evaluation, passed on the screen representation of the lighter tone patches, is that the i1 is "cleaner."
Not sure how you evaluated this (assigned profiles made with each spectro to the image or what?) but if the raw measurements are telling you that the EyeOne Pro is measuring lighter or whatever, a profile made from this instrument would have the opposite affect in the final print. IOW, if the spectro is measuring lighter and this profile is used as a destination profile, the printed result would be darker since the profile conversion would attempt to "correct" for the lighter appearance of one spectro vs. another. Only way this would NOT be true if both source and destination profiles were make with the same instrument. Make sense?
Regards,
Terry
______________________________________
Terence Wyse, WyseConsul
Color Management Consulting
G7 Certified Expert
FIRST Level II Implementation Specialist
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