Similar. You intentionally underexpose the film when you shoot, pretending that it has a higher ASA rating than it actually does. You then increase the time a

Similar. You intentionally underexpose the film when you shoot, pretending that it has a higher ASA rating than it actually does. You then increase the time and/or the temperature when developing the film, to compensate for the underexposure. You end up with a correctly-exposed image, but at the cost of extra grain, extra contrast, etc.