Solving Digital Photography Contrast Problems

The registration capacity of negative emulsions is superior to that of photographic paper, because the negative describes the tones of the original scene with transmission densities, while with paper reflection densities are used, were the range is much more constricted. If we set the exposure latitude of a negative of normal contrast in five exposure values (32:1), it is precisely because this is the maximum exposure latitude of paper . With the contrast control we try to maintain the density interval of the negative in some limits that make the printing as different tones possible.

Now: in a low characteristic contrast emulsion, this maximum relationship of densities is given for a exposure level interval greater than 32:1, and in a high contrast film, for an smaller interval..

Nonetheless, besides our control, an image frequently exceeds this maximum contrast we can register on paper. When this happens, we loose detail in the lights or in the shadows because it's density in the negative differs too much from the correct exposure zone and, in the print, the zone appear indistinctly black or white. In other cases, an image is made up of zones of different and very separate densities, or by zones of similar densities who's difference we'd like to accentuate.

In a large amount of cases like these it is necessary to intervene in the distribution of grays we have not only through the characteristic contrast but also with a selective exposure of the different zones of the image

The limitation of the exposure level that the different zones of the print receives is called shading . This technique lets us modify the distribution of the tones once we have chosen a paper of a determined characteristic contrast. It is usually used when the zone to be corrected is very limited. Once the exposure level is obtained for the different zones, a mask is made with dark cardboard cut in the appropriate shape for the shades; then we cover them with the appropriate mask and make the exposure even longer. We have to avoid the outline of the cardboard forming a noticeable outline on the paper, which is achieved by holding the mask a few centimeter above the paper and softly moving it to cause a degradation from one zone to another. Nonetheless, this system has it's limits since it is not possible to alter the contrast very much without the shading becoming evident on the borders.