3. The calibration must be performed with an apparatus for the determina-
tion of diffuse density which is in accordance with the standards.
L. The individual properties of the density measuring instrument must be
known in order to be able to correct in particular non-linearities
of the receiver.
To the objection that for many measuring tasks the knowledge of the rela-
tive density values appears sufficient, the following be replied:
&. if possible internationally uniform measuring methods and
measures should be applied;
b. non-linear measuring properties of densitometers and micro-
densitometers falsify the relative density values as well.
| At last be demonstrated by means of the following tabulation which amount
‘9 of errors were found in the computation of the gradation y in the de-
scribed experiments. The gradation is an indispensable quantity for all
continuing computations, e.g. in the derivation of reflection features
of topographical objects from image densities. The same applies to in-
vestigations on modulation transfer characteristics of photographic
images.
Table: Errors of gradation y (in per cent of the theoretical value).
The step wedges printed onto the diverse film types were prints
of the Kodak step tablet no.3. The gradation was evaluated from
the diffuse densities of the original step tablet no.3 and the
prints. For one time y was determined from the reference measure-
ments after DIN 4512 with the apparatus of the PTB, the other
time y was evaluated from the results of the measuring instruments
investigated. The dots (°) are errors < 3%, at (-) no evaluation
was performed.
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11
