Common Terms

Terminology in photography has changed slightly since the rise of professional digital cameras to include information on digital equipment such as light sensors, as well as techniques for using computer software to enhance images. The definitions below represent common terms used in general and crime scene photography. For additional glossary terms see the SWGDE and SWGIT Digital & Multimedia Evidence Glossary or the All Things Photography website.

Ambient Light - Light already existing in an indoor or outdoor setting that is not caused by any illumination supplied by the photographer.

Aperture - opening in the camera that lets in the light.

Aspect Ratio - The ratio of width to height in photographic prints; a ratio of 2:3 in 35 mm pictures produces photographs most commonly measuring 3.5 × 5 inches or 4 × 6 inches.

Camera Angles - Various positions of the camera (high, medium, or low; and left, right, or straight on) with respect to the subject, each giving a different viewpoint, perspective or visual effect.

Capture - The process of recording data, such as an image, video sequence, or audio stream.

Color Correction - To correct or enhance the colors within an image.

Contrast - The difference in darkness or density between one tone or another.

Cropping - Removing portions of an image that are outside the area of interest.

Depth of Field - The area between the nearest and farthest points from the camera that are acceptably sharp in the focused image.

Evidence Quality Photos - Images of sufficient size and quality to allow comparison and examination by a qualified forensic expert.

Exposure - The quantity of light allowed to act on photographic material; a product of the intensity (controlled by the lens opening) and the duration (controlled by the shutter speed) of light striking the film or sensor.

F-stop - Lens setting number indicating the size of the aperture that allows light into the camera. It is an inversely proportionate number, so that f/1.8 indicates a larger opening than f/5.6.

Filter - A colored piece of glass or other transparent material used over the lens to emphasize, eliminate, or change the color or density of the entire scene or certain areas within a scene.

ISO Speed - The sensitivity of a given film or sensor to light, indicated by a number such as ISO 200. The higher the number, the more sensitive or faster the film or sensor.

Lens Speed - The largest lens opening at which a lens can be set. A fast lens transmits more light and has a larger opening than a slow lens. For example, f/1.8 would set a larger opening than f/5.6 and would, therefore, be a faster lens.

Raw File - The data captured by a digital camera sensor before it is converted into an image file by software, either inside the camera or on a stand-alone computer.

Resolution - In a digital photograph, the number of pixels which make up the image.

Scale - The relative size of an object as compared to other objects in general proximity. Also refers to a measuring device or set of marks to indicate object size in a photograph.

Shutter - Blades, a curtain, plate, or some other movable cover in a camera that controls the time during which light reaches the film.

Working Copy - A copy or duplicate of a recording or data that can be used for subsequent processing and/or analysis.

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