Chapter 5: How Film Works
Figure 5.8: This graph shows where the reference tones on a gray card lie along the green curve of a color emulsion. If we project the gray card exposure down to the bottom scale, we see that the gray exposure becomes the zero point and the white is 21/3 stops brighter than gray.
Figure 5.9: An overexposed gray card.
steps between white and black. Certain high-contrast fi lms used for mattes and titles are pretty close to being just black and white with no gradations at all. In a lowcontrast fi lm, the curve is much flatter and will contain many variations of gray along a large exposure range with less density at the top. Most negative fi lm has this lowcontrast feature and has a gamma of around 0.65. The rounded-off number 0.65 is derived by dividing the rise over the run in the straight line of the curve. So if the negative fi lm goes up in density from 1.00 to 1.19 over a one-stop increase of 0.30 on the exposure line, that is a rise of 0.19 divided by the run of 0.30, or 0.63, which is the gamma, or contrast, of the fi lm. The fi lm that the print will be made from is a higher contrast fi lm of about 2.0. The reason for this seemingly peculiar mismatch is that a low-contrast negative can capture a much broader range of light than a higher contrast fi lm. Film can capture a range of light spanning 8–10 stops
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