Camera Film Underexposure: Digital Camera Basic Theories

The minimal density we can see on a negative corresponds to the density of the base of the film (or of the unexposed emulsion), which we can see in it's borders. From that level on, the densities of the different zones of the image depend on the density formed on the emulsion. A transparent zone on a negative (maximum density on a slide) indicates insufficient exposure ( underexposure ), inferior to the minimal level for density to be formed on the emulsion ( underexposure limit ). The zones of the image that received a slightly greater exposure than that limit appear as very light densities, similar and hard to distinguish from one another. These zones of the image appear like that because it's corresponding zones in the scene were gloomy, but, above all , because the exposure value selected implies an insufficient exposure level for that part of the image. The corresponding zone of the original scene probably had details and tones we could see, but when passed to our photographic image have disappeared. Underneath a minimal exposure level the density is NOT proportional to the brightness.

Overexposure

The maximum density of a zone on the negative image (transparent on a slide) indicates: excessive exposure level, above the corresponding maximum density the emulsion can give. Above this level all brightness of the scene are registered also with the maximum density, and therefore undistinguishable (burned on a slide). Even if on the original scene there were different high lights, there overexposure has destroyed the detail. We have lost the description of the lights framed in the scene.

Correct Exposure

Between those two extremes we can observe a variety of densities proportional to the different brightness of the scene: precisely the ones that, when making the photograph, received an exposure level above the minimum and below the maximum. In this brightness interval of the scene, and as consequence of the exposure value selected when shooting, we have a detailed reproduction of the tones, we have an image.