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The Kodachrome transparencies were projected, one at a time, with a Kodak Master Model Projector. The screen luminance was about 15 ft-L.
The Ektachrome transparencies were displayed on an illuminator having a viewing-panel luminance of 400 ft-L, in a normally lighted room, and were judged by fifteen observers, who again used the form shown in Fig. 1 for recording judgments.
Interpretation of Data
The present report is confined to a study of the curves in Figs. 3 through 8, which were derived from the judgment data, showing tone-reproduction quality as a function of the logarithm of the camera exposure. Camera exposure has been defined2 as follows:
where Ee is camera exposure, t is time expressed in seconds, and /is the aperture ratio. Since / is dimensionless, camera exposure has the dimension of time and is expressed in seconds. A camera exposure of 1 sec can be obtained, for example, by exposing for 1 sec at //I, 4 sec at//2, 16 sec at//4, etc.
The values of quality for each camera exposure were obtained from the judgment data by averaging the ordinates measured on the judges' sheets, and the curves in Figs. 3 through 8 were plotted. The materials represented by these curves are as follows:
A. Eastman Plus-X Panchromatic Negative Safety Film, Type 5231.
B. Eastman Background-X Panchromatic Negative Safety Film, Type 5230.
C. Kodachrome Film, Daylight Type.
D. Kodak Ektachrome Film, Daylight Type.
Figure 2 illustrates the measurements which were made on all the sets of curves, and which will be described below.
It presents two hypothetical curves showing the relationship between quality
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Log EC
Fig. 2. Hypothetical curves showing methods of measuring latitudes, relative speeds and relative exposure indexes of two materials used to photograph the same scene. These values for this scene are respectively the antilogarithms of (a) the widths of the curves at 95% of the peak value, (b) the distance between the left ends of the horizontal lines at this level, and (c) the distance between the midpoints of these lines.
and log camera exposure for two materials, X and F, when used to photograph the same scene. The scene characteristics which might affect the maximum quality, exposure latitude, and optimum exposure on each material have been taken into account by the judges in their quality ratings from which these curves were obtained. A direct comparison between the properties of the two materials revealed by these curves can therefore be made without further consideration of the scene characteristics. A number of similar sets of curves will provide increasingly useful information about the relative performance of the two materials.
An obvious conclusion which can be drawn from an inspection of the curves in Figs. 3 through 8 is that, since the curves are fairly smooth, quality varies uniformly with log camera exposure. This is something which might not be predicted from a casual inspection of the judgment data, since there were very large differences of opinion among the judges, both as to the quality of the reproduction of any given scene and the
Sorem: Effect of Exposure on Tone-Reproduction
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