From Todd and Zakia’s Photographic Sensitometry: The Study of Tone Reproduction p. 286:
“The densities of the aim reflection print are about 0.25 below the 45 degree reference line. The slope of the midtones is slightly greater than 1.0 – between 1.1 and 1.2. Prints with midtone slopes less than 1.1 are characterized by viewers as flat. The slope of the extreme shadows is nearly 1.0. These observations confirm the belief that shadow detail must be maintained for such (pictorial) subject matter if the print is to be satisfactory, whereas highlight detail is far less important.”
“For portrait photography, the aim curve is to the right of the one shown in Fig XIII-3 and the slopes are increased in the highlight and midtone region, at the expense of the shadow reproduction. No doubt this change arises from the importance of skin tone reproduction.”
Tone Reproduction - Photograhic Sensitometry.jpg
Right is darker and left is lighter.
It would appear general pictorial and portrait photography require preferred reproduction curves that are almost opposite in appearance. So if the preferred curve in Digital Color Management is for portraiture, that would explain why I thought it looked inverted.
The reference line in Digital Color Management does reflect the original subject values, but the reference line used with my program and in most books, isn’t exactly meant for the same purpose. Strobel et al Photographic Materials and Process, p. 356. “The 45 degree reference line is arbitrarily located so that its lower point corresponds to a diffuse white object in the scene and the minimum density of the photographic print material. If the luminance in the scene were produced exactly in the print, the resulting tone reproduction would have a slope of 1.00, matching that of the reference line. In fact, the average curve for first-choice prints is located 0.2 to 0.3 density units below the 45 degree line except in the highlight region, where the curve cannot go below the minimum density of the paper. The curve shows low slope in the highlight and shadow regions, but has a gradient of 1.1 to 1.2 in the midtone area. This indicates the print’s highlights and shadow regions are compressed compared to the original scene, while the midtones have been slightly expanded in contrast. The results in all cases were remarkably similar to that shown in Fig 11-1. Whenever the departure from the desired slopes was greater than 0.05, the observers invariably judged the prints as being unacceptable in contrast, indicating very narrow tolerance levels. Consequently, it appears that the desired objective tone reproduction in black and white reflection print are essentially independent of the characteristics of the original subject.”
Tone Reproduction - Photograhic Materials.jpg Tone Reproduction - Photograhic Materials 4 quad.jpg
And from Photographic Theory of the Photographic Process 3rd ed, p 467: “Whenever the density level of the prints was great enough so that the curves closely approached the 45 degree reference line, the prints were unanimously rejected because they appeared too dark.”
Last edited by Stephen Benskin; 03-09-2013 at 09:56 AM. Click to view previous post history.