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HANDBOOK OF PHOTOGRAPHY 



quadrant for the resultant D-logio E characteristics of the developed positive material 

 printed from the negative, the fourth quadrant for the variation of the eye response 

 when viewing the subject and when viewing the positive-print reproduction, and the 

 first quadrant to compare the resulting visual sensation when comparing the positive 

 reproduction with that of the original subject. This diagram is shown in Fig. 30. 



Starting from the scale of subject brightness (logio B scale) which determines the 

 exposure and exposure range, we find the H and D characteristics of the developed 

 negative as given in the second quadrant. True tone rendition is obtained on the 



Relative SubJec+iVe 

 Contrast Curve 



Positive characteristic 



Reproduction 

 — Actual 



J-— ^/Negative characteristic 



Fig. 30. — Four-quadrant diagram illustrating the method of determining correctness 

 of tone reproduction. This diagram provides a method by which the final print can be 

 compared with the original subject; it does not take into account tone variations which may 

 be desired for aesthetic purposes. 



straight-line portion of this curve. From the D-logio E curve of the negative, we 

 arrive at the same characteristic of the printing material (third quadrant) through the 

 process of printing or making the positive. Here again, true tone rendition is obtained 

 over the straight-line portion of the characteristic curve of the positive material. 

 However, the curvature of the characteristics of the printing material are such as to 

 exaggerate, rather than compensate, for tone distortions occurring in the negative. 

 Finally, by viewing the positive or print by reflected light, we obtain the scene bright- 

 ness through the brightness characteristic of the human eye which translates the scene 

 brightness into visual sensations. By comparing the visual sensations thus produced, 

 with the subject brightness, we obtain the curve in the first quadrant, which represents 

 the distortion characteristics of the final print reproduction. If this characteristic is a 



