A negative is an image on a strip of transparent cellulose based film, in which the lightest areas of the emulsion appears the darkest and vice versa. The colors are also reserved into their respective complementary colors in case of color negatives. By projecting the negative onto a photographic paper with an enlarger, a positive print can be created. The result of the second reversal is achieved because the paper is also darkened in proportion to its exposure to light which restores light and dark to their normal order.
Bracketing is a general technique of taking a multiple shots of the same subject by using different camera setting. When the exposure of the scene is very dynamic, bracketing technique comes handy. By taking the same subject with different exposures and stitch them together in post, a picture with a higher dynamic range can be achieved.