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Re: Colorsync-users Digest, Vol 4, Issue 449

Hi Mark,

I'll try to answer your questions in order...but there really aren't simple answers. Factors such as optical geometry and polarization often have much bigger impact on measurement accuracy than any of the spectral issues.

1. In the absence of that scientific instrument you are searching for in the X-Rite's basement, is it valid to conclude from your comments that an instrument like the EyeOne Pro will provide a better spectral description of a monitor and therefore a more accurate profile, all OTHER things being equal?

I don't think that you can make a general comment about a spectro being better than a colorimeter in every instance. It depends highly on the spectral structure of the source and the characteristics of the spectro itself. It also is highly dependent upon what you are trying to measure. Generally a colorimeter will measure into the darker regions better than a spectro. A spectro can certainly measure dissimilar sources with smaller differences relative to a reference spectrophotometer, than a colorimeter. The biggest issue with a spectro is the bandwidth of the device. A product like our i1 has a relatively large bandwidth (I'm at home and don't have the spec in front of me so I won't quote it) A great deal of effort is spent in the calibration of the device characterizing the operating characteristics as it measures a number of different references, both emissive and reflective. It is still very difficult to get an i1 to match a minolta CS1000 or pr650 measurement on an arbitrary display. It is also difficult to get a CS1000 and pr650 to match on every display. As the gamut of a display starts to approach the spectral locus, the situation becomes very tenuous. If I was measuring a wide dynamic range, wide gamut display, I would personally pick a colorimeter. That colorimeter would be calibrated by spectral reference device. If I was trying to get displays of greatly different spectral characteristics to match (CRT to LCD), I would probably want a spectro photometer. So as a generalization, wide dynamic range, known emissive characteristics, -> colorimeter. Smaller dynamic range, arbitrary spectra, -> spectrophotometer.


2. Will the spectrophotometer always be a better instrument when comparing the spectral qualities of different types of monitor - CRT, LCD, LED...

As I said above, if I was comparing devices or trying to calibrate different technologies to the same aim, I would likely default to a spectro. I would argue that things start to get very difficult when trying to compare absolute measures of Yxy, particularly with the shorter wavelength greens used in many wide gamut displays. On LED displays, we have to consider that the center wavelengths change with temperature. This is a real serious issue when comparing measurements between instruments. You really do have to wait for 30 minutes to an hour before doing any serious measurements of an LED output. 

Regards,
Tom


Message: 1
Date: Sun, 09 Dec 2007 08:10:00 +1100
From: email@hidden
Subject: Re: LED displays: some comments and observations.
To: email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1

Tom,

Just to recap... If I remember rightly the discussion about LEDs sprouted from the Samsung XL20 and the possible discrepancy in profiling that may arise from using two different colorimeters - the Huey and the i! Display. I reflect on the notion that gained currency recently (at least in some quarters) that colorimeters, in general did a better job than a Spectrophotmeter when profiling monitors because of their 'tristimulus architecture'. (Hope that doesn't sound like B. S. but without a technical background it's the best I can do!).

1. In the absence of that scientific instrument you are searching for in the X-Rite's basement, is it valid to conclude from your comments that an instrument like the EyeOne Pro will provide a better spectral description of a monitor and therefore a more accurate profile, all OTHER things being equal?

2. Will the spectrophotometer always be a better instrument when comparing the spectral qualities of different types of monitor - CRT, LCD, LED...

Mark Stegman




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