There’s a lot not covered. The quote in post #45, is only the basic conclusion. A good section of the chapter goes on to support the statement. It even discusses how the eyes response to different levels of illuminance and different luminance ranges.
Now, here’s the example of a referred print tone reproduction curve from The Theory of the Photographic Process.
Preferred tone reproduction curve - preferred print.jpg
Notice the luminance range of 2.20. This is considered the statistically average luminance range. It also doesn’t include specular highlights and accent or cavity blacks. More on this later.
From the text’s discussion of the above example, “The tone-reproduction curve in Figure 22.2 is an average of the curves obtained for the first-choice prints in the experiments of Jones and Nelson, and Jones and Condit, who made and studied several thousand black-and-white prints of approximately 170 outdoor scenes. Fifteen to twenty prints differing in contrast, density, and tone reproduction curve shape were produced for each scene. The prints were viewed with an illumination of 100 footcandles and judged for subjective quality by a number of observers.”
“For scenes having unusually long log luminance ranges (2.5 – 3.0), the tone reproduction curves for the first choice prints were slightly to the left of the curve shown in Figure 22.1 (above). For scenes having unusually short log luminance ranges (1.5 – 1.9), the corresponding curves were slightly to the right of this curve. Scenes of normal log luminance ranges (2.0 – 2.4) gave curves that were essentially identical with the curve shown in the figure.”
Slightly later in the chapter, “Consequently, the characteristics of the human eye rather than those of the photographic paper appear responsible for the necessity of making reflection-type black and white prints about 0.25 less dense than the hypothetical print, represented by a 45 degree line, that would reproduce the luminance ratios or log luminance differences of the original scene…The eye is apparently able to compensate adequately when the luminance differences are about one-fiftieth those of the original scene, and thus make the photograph look like a sunlit scene, but not when the luminance differences are one-hundredth of those of the original scene. The slope of 1.15 required in the middletone region of the curve is also probably related to the characteristics of the eye. The reproduction gradient in the highlight region is sacrificed in order to fulfill the need for a middletone gradient greater than 1.0.”
I hope it's becoming apparent why I constantly encourage people to understand theory. Chapter 20 in The Theory of the Photographic Process 3rd edition is entitled The interpretation of Sensitometric Results. After all, what good are curves if you don't know how to read them?
Last edited by Stephen Benskin; 03-07-2013 at 08:49 PM. Click to view previous post history.