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R2-29 report 2004-06-08.ppt/Bp © METAS - 1

m ae t s metrology and accreditation s witzerland

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Dr. Peter BlattnerSwiss Federal Office of Metrology and Accreditation

METAS

R2-29 (2nd report) Characterization of Imaging Luminance

Measurement Devices (ILMDs)

video photometer, imaging photometer, CCD luminance meter



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Conclusion of the 1st report

•from metrological point of view ILMDs are complex systems (traceability, software validation, etc)

•the parameters defined by CIE 69-1987 are not sufficient to characterize ILMDs

•there is some interest from industry to have some guidelines on how characterize ILMDs

Prepare a Technical Report on methods for the characterization of imaging luminance measurement devices

TR:



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Progress since the last meeting

Discussions with several users and manufacturers:

• more products/manufacturers on the market• increasing number of devices were sold• more quantities that are measured/deduced

-> new applications

• some inconsistencies are found between different users in some specific cases



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Quantities derived with ILMDs (1)

• Luminance distributions-> Display, lamps, filaments

-> tunnel lightening

© TechnoTeam GmbH



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• geometrical parameters (angles,…)

•“partial” vertical illuminance

•Physiological glare



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- >Analysis of complex sceneries

© TechnoTeam GmbH

• Illuminance distributions

• UGR



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• luminance coefficients - > Analysis of non

uniform surfaces

• angular dependant luminance distribution

-> near field goniophotometry

• (color coordinates)

- > colorimetry



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Discussions with users

•Some differences in measurements of the same sample were found between different users having different systems (differences up to 20%)

Explication: - Measurement task: measurement of luminance distribution of displays with LED backlights.

This is inherit to ILDMs: partial filtering is not applicable and there is only a limited number of glass fiters available.

© TechnoTeam GmbH

One has to life/dealwith that problem !

The situation is even worse when grayfilters have to be used

•Most users are „happy“ with the system they were using

However: best possible f1‘ that can be done on ILMDs is in the order of 2.5%



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Discussions with manufacturers

•There is a limited interest from industry to have some

internationally agreed guidelines on how to characterize

ILMDs.

•The characterization problems are solved mostly within

the industry.

•Some procedures are part of the “in-house” knockledge

of the manufactures.

•One manufacturer is strongly in favor for a CIE-TC (and

would like to chair a possible TC).



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•Close R2-29, new TC to generate a „User‘s guide“

•Close R2-29, new TC to generate guide for characterizing ILDMs

•Close R2-29, no action (yet)

Some of the problems are not specific to ILDMs but to LDMs

Only a few number of manufacturers are concerned

How to go on?

What to do with the parameters in CIE 69-1986 that are not applicable or missing?



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• deviation of relative spectral responsivity from the V(l) function - > f1‘

• UV response, IR response -> u, r

• directional response -> f2(g)

• effect from the surrounding field -> f2(u)

• linearity error -> f3

• error of display unit -> f4

• temperature coefficient -> a

• fatigue -> f5

• modulated radiation -> f7

• polarization -> f8

• range change -> f11

• error of focus -> f12

• lower/upper frequency limit -> fl, fu

properties of luminance meter as defined by CIE publication 69-1986



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properties of video camera system

• number of pixels (total, effective, output)• cell size• frame rate• shutter speed• noise• dynamic range• photo response non-uniformity (PRNU)• dark signal non-uniformity (DSNU)• defective pixels• optical imaging parameter (MTF, distortion, etc)



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CIE publication 69-1986: inconsistencies, missing parameters

gloss trap

measurement field

Examples:

• measurement of the effect of the surrounding field

• spatial homogeneity

(shading: depends on aperture, focusing distance)

• cross talk between neighbor pixels

(blooming, smearing,data compression, etc)



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other problems associated with ILMDs

• timing problems (integration time : 0.01 msec - 1 sec)

• dark current (resp. drift of dark current), depends on temperature,

position

• fixed aperture/ focus versus variable aperture/ focus

• image compression

• straylight

• dynamic range

• polarization

and finally

• data acquisition, manipulation, and evaluation made by a computer. There

is always a mathematical transformation between the luminance value and

the pixel value, typically

luminance(x,y,t) = (pxl (x,y,t) - dark(x,y) - dark(t)) * calibration * shading (x,y) * nonlinearity (pxl)

luminance(x,y,t) = pxl (x,y,t) * calibrationideal:

real:

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