Measure Relative Intensity (Contrast) in a Digital Camera

It's worth it to stop and observe the contrast of the scene we have framed, independently of the general brightness, high or low. The variation of reflected light intensity we measure with a photometer in the different zones of a frame may be very large. The backlights, lateral or pinpoint lights, the depth, the relief, the different reflectance of materials, are usually sources of large variations. Diffused or frontal light, the homogeneity of the surfaces referring to the orientation, reflectance and texture give way to a much less accentuated contrast.

Our sight allows us to observe scenes whose zones can have very different brightness. Nonetheless, the latitude of the photographic materials and the digital systems is infinitely less (4.3.2, 4.8.2 and 4.9.2); the latitude expresses the maximum contrast that the emulsion or the digital camera can register with detail; the latitude of the film is variable according to the type and developing, and we can express it as an interval of an amplitude of n exposure values. Measuring the intensity of the different zones of the frame we can express the contrast of a scene as an interval of a determined number n of

exposure values or also as the relation between extreme brightness. Generally, the expression of the contrast is made in the form of 2 n :1, were n is the number of exposure values (or “diaphragms”) of the interval's amplitude. For example, a scene with a brightness interval of three exposure values is usually indicated more frequently as 8:1 (the lights have an intensity eight times - three exposure values- greater than the shadows).

Whatever it is, when comparing the brightness interval of the scene with the exposure latitude we will be able to have a clear idea of what will happen with all the zones of the frame in any exposure level (4.3.1.2).

This is the foresight of the image not how we see it, but how the film sees it, and lets us know before shooting if what we want to make it possible, something that with a digital camera we can see directly on the screen; the foresight in the case of film and the digital camera's viewfinder provides us a clear criteria to reach the correct exposure value; in case what we're pretending isn't possible, we are always able to modify the frame, the point of view and the illumination .