Your country’s flag on a sunny day: Easy enough to say how it should reproduce in a color photograph. But in black-and-white? There is no hard-and-fast rule about the shades of gray most appropriate to a colored image. Over a period of many years beginning in the early forties, that issue was the subject of some fascinating research by men such as L.A. Jones, C.N. Nelson, H.R. Condit and others. The topic was termed “tone reproduction” and was concerned with how scene elements of varying luminance were best reproduced as shades of gray in a black-and-white photograph.
These gentlemen selected 170 outdoor scenes and used a telescopic photometer to meticulously characterize the luminance of various elements in the scenes. They made many photographs of each, varying film, development, and camera settings, and made dozens of (straight) prints with various papers and printing times. The prints were examined in typical room light (about 100 foot-candles) by many observers and rated for “quality.” Each print was also characterized by a tone-reproduction curve that related luminances of its scene elements to the reflection densities at which they were reproduced in those prints. Surprisingly (or perhaps not), the prints ranked highest for quality all had astonishingly similar tone-reproduction curves. That preferred tone-reproduction curve, three versions of it, are reproduced here. The three curves correspond to three values of Dmax, typical of papers of the era. We have included a straight line of unit slope, which was long anticipated to be the preferred curve, as it spaces reflection density in direct proportion to log scene luminance.