Highlight headroom is the measure of how much additional

dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base- ...

a given photographic medium (such as

film A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...

or digital image sensors) has to record the detail within the brightest parts of a scene. As an example, consider a photograph of a white

wedding dress A wedding dress or bridal gown is the dress worn by the bride during a wedding ceremony. The color, style and ceremonial importance of the gown can depend on the religion and culture of the wedding participants. In Western cultures and Anglo-S ...

against a white background. With limited highlight headroom, it will be hard to appreciate the intricate details within the fabric of the dress. The higher the available headroom, the more subtle shades of white will be captured. In practice, photographers are often faced with photographing outdoors on a cloudy day, but with the sun shining through a gap onto the subjects forehead. This can often lead to a bright reflection which records as bright white. If this bright spot (called a highlight) lies at the edge of the persons outline (from the camera's perspective) then it may end up blending into the cloudy sky if there is insufficient highlight headroom. This is a particular problem with

digital camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices ...

s which often have a smaller

than film. Digital sensors typically have an abrupt cut-off at the peak white level; sensor output typically increases linearly with incident light level until a peak white level, after which higher light levels result in the same peak output from the sensor. The response of film when the incident light is near the white level of the film is more gradual.

References

Science of photography {{Film-term-stub