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IS0
IN TERN AT I ON A L ORGAN IZATl O N FOR STAND AR D IZATl ON
IS0 RECOMMENDATION
R 782
MICROCOPY
MEASUREMENT OFTHESCREEN LUMINANCE OF MICROFILM READERS
1st EDITION
July 1968
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 782, Microcopy - Measurement of the screen luminance of
microfilm readers, was drawn up by Technical Committee ISO/TC 46, Documentation, the Secretariat
of which is held by the Deutscher Normenausschuss (DNA).
Work on this question by the Technical Committee began in 1954 and led, in 1967, to the
adoption of a Draft IS0 Recommendation.
in March 1967, this Draft IS0 Recommendation (No. 1056) was circulated to all the IS0
Member Bodies for enquiry. it was approved, subject to a few modifications of an editorial nature,
by the following Member Bodies :
Belgium Hungary
Portugal
Romania
Brazil India
Sweden
Canada Ireland
Israel Switzerland
Chile
Czechoslovakia Italy Spain
Denmark Japan U.A.R.
France Netherlands United Kingdom
Germany Norway U.S.A.
Greece Poland
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in July 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 782-1968 (I
IS0 Recommendation
R 782 July 1968
MICROCOPY
MEASUREMENTOFTHE SCREEN LUMINANCE OF MICROFILM READERS
INTRODUCTION
The screen luminance of a microfilm reader is an essential factor of eye comfort. However, while
certain essential requirements of the human eye as regards luminance can be defined physiologically,
it is more difficult to characterize a microcopy reader screen simply by one or more luminance values
corresponding to these physiological requirements.
The experts hesitated in particular between two very different methods of measurement of screen
luminance. .4 first method could consist in taking luminance measurements perpendicularly to the
screen and over its entire surface; a second method could consist in futing the measuring instrument
opposite the centre of the screen and taking the luminance measurements by swivelling the instrument.
In practice, and especially with translucent screens, the results obtained with each of these two
methods are fundamentally different. Moreover, the first one is not always practicable, owing to the
geometrical layout of the apparatus.
ïo approximate as closely as possible to the actual conditions of use of the readers, it seemed
necessary to combine the two methods by splitting the surface of the screen into separate areas
and examining each area according to precisely stated rules.
The width of 21 cm given to these areas was not futed at random. Physiologically it represents,
margins included, the expanse which can normally be scanned by the eye of an observer glancing at
a written text.*
of 33 cm between screen and measuring instrument corresponds to the normal reading
The distance
distance for a text of the width specified above.
Finally, it was not deemed essential to reproduce the exact conditions of binocular reading because
the method adopted covers slanting measurements. While involving a far smaller complication, this
feature permits indirectly analysing the differences in luminous perception which may be experienced
by the two eyes when observing a single point from different angles.
The proposed method of measurement cannot alone solve the problem of adapting the luminance of
microcopy reader screens to the physiological requirements of the human eye. At a later stage, mini-
mal luminance values will have to be determined, as well as the maximal values of the luminance
logarithmic differences (see clause 4.2.1) on one and the same screen.
The results obtained with both opaque and translucent screens are comparable within each category
but differ more from one category to the other.
However, the method will allow comparison of the performance of various readers available on the
market and should lead to improved equipment.
*
See IS0 Recommendation R 216, Trimmed sizes of writing paper and certain classes of printed matter,
standardizing a width of 210 mm for writing paper and some types of printed matter.
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ISO/R 782-1968 (E)
1. SCOPE
This IS0 Recommendation describes a method of measurement associating with various points of a
microcopy reader screen
data representing luminance values and expressing the impression of luminance produced
(a)
on an observer facing the screen;
data representing luminance logarithmic differences and expressing the impression of
(b)
luminance uniformity produced on an observer facing the screen.
2. FIELD OF APPLICATION
2.1 This IS0 Recommendation applies to microfilm reading apparatus having translucent or built-in
opaque screens. It does not apply to apparatus using virtual (aerial) images, nor to apparatus in
which the conditions of clauses 3.4 and 3.5 cannot be followed. Moreover, this IS0 Recommen-
dation does not apply to apparatus for reading microcards.
2.2 If the screen is not built into the apparatus, the measurements described in this IS0 Recom-
mendation should be made only on a screen the characteristics and position of which conform
to normal conditions of use, as specified by the manufacturer.
2.3 In particular, apparatus known as office apparatus, in which the image is formed on a sheet of
white paper laid on a table, may be either classed with built-in opaque-screen readers or assessed
by measuring the intensity of illumination they can provide, under conditions which have to be
agreed by the parties concerned. if the method of likening the apparatus to a built-in opaque-
screen reader is used, it is the manufacturer's responsibility to supply, in support of performance
claims for his apparatus, the sheets of paper which enable them to be verified.
3. METHOD OF MEASUREMENT
3.1 Measuring instrument
Whether the screen be opaque or translucent, the measurements should be made with a lumi-
nance-meter.The angle of acceptance fl of the luminance-meter is the angle between the two
straight lines EF and EG, E being the point on the screen located in the luminance-meter axis,
F and G two points of the luminance-meter aperture (see Fig. 1).
Screen E
lu minunce-me ter
I
FIG. 1 - Diagram showing the definition of the angle of acceptance
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ISO/R 782-1968 (I
3.1.1 The angle of acceptance of the luminance-meter should preferably be 2" 45'. If the lumi-
n
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