Part of the equation left totally out of the question is that negative film has a wider dynamic range than the vast majority of the papers used to make photographic prints.

For example, in the time when Ansel Adams did his most significant work, the monochrome films he used had around 10-11 stops of dynamic range, but the papers available for him to print on were limited to around 6-7 stops. For modern color film, the dynamic range is a little reduced compared to B&W film, but so is the dynamic range of color papers compared to B&W papers.

Where does this latitude for exposure come from: is it in the film, in the developing process, or in the printing process?

Yes, yes, and yes. Some of it is from all three parts of the process.

Film

Film itself works by chemistry. The rate at which chemicals react to being exposed to light varies based on how much of the chemicals in the emulsion have already reacted to light. As film is exposed, it takes longer and longer to double the amount of silver salts that have reacted to light. This is because the longer the film is exposed, the amount of unreacted chemicals in the emulsion per unit area becomes less and less as the portion of the emulsion that has already undergone a chemical reaction in response to light is no longer able to absorb more photons.

So the closer an area of a film is to full saturation, the more light it takes to push it even closer. This is what is often referred to as the "shoulder" of film response curves. Digital, in contrast, is purely linear all the way to the saturation point, so it is much easier to clip highlights with digital than with film.

One easy way to understand this is to consider the Schwarzschild effect, sometimes referred to as reciprocity failure. For conventional B&W and color films exposed for longer than one second or so, doubling the exposure time does not make the image twice as bright. To do that the exposure time must be extended, sometimes rather significantly. Just how much more time is needed varies from one film to the next. Manufacturers of film usually publish data sheets that, among other things, specify the needed adjustment for long exposures when using a specific film they produce.

Development

Altering exposure times and development times can increase or decrease the overall contrast of an image. If a scene with a wide dynamic range is shot, that dynamic range can be compacted into fewer stops by reducing contrast. If a scene with a limited dynamic range is shot, that limited dynamic range can be stretched by increasing contrast.

Printing

Developing the latent image on an exposed piece of film is only half the process, though. The other half is using that developed negative to produce a print. Making a print from a negative uses light in much the same way that capturing a latent image on a piece of film does. The exposure of the photosensitive paper can be controlled by the amount of light used. The amount of light allowed to reach the paper is controlled by several things:

• The intensity of the light
• The density of the developed negative
• The amount of time the light is on and shining through the negative and striking the surface of the photosensitive paper.

In addition, darkroom techniques such as dodging and burning can be used to develop specific areas of the photo paper for longer or shorter amounts of time than the overall print. This is usually accomplished in the darkroom using masks shaped to block some of the light shining from the enlarger head onto the photo paper. With contact prints, the masks block the light before it reaches the negative.