PHOTOGRAPHY GLOSSARY "D"

Dark Frame. A noise reduction process where a camera takes a second exposure of a black frame after the camera takes a long exposure image. The image noise is easily identified in the black frame shot and is then electronically removed from the actual image. This helps to reduce the amount of hot pixels that normally show up in long exposure shots from digital cameras.
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Decompression. Process by which the full data content of a compressed file is restored.
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Dedicated Flash. An Electronic Flash Unit that is made to be used directly with a specific make or model of a camera. Canon, Nikon Minolta and Olympus for example, all have electrical contacts in the hotshoe which passes TTL (through the lens) metering and AF range information to and from the flash unit or speedlight. You cannot interchange flash units and cameras. I.e. a Nikon speedlight on a Canon camera.
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Depth of Field. (DOF). The range of items in focus in an image. This is controlled by the focal length and aperture opening of a lens. A large or wide aperture gives a shallow depth of field (not much range in focus) and a smaller or narrow aperture give a large depth of field (more range in focus).
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Digital Film. Quite simply that. Solid state flash memory cards in place of emulsion film.
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Digital Zoom. A digital magnification of the centre 50% of an image. These give less than sharp images because the new zoomed image has been interpolated. Don't be swayed by the incredible 500% zooms on some cameras, the images won't be really acceptable. The optical zoom gives much more clarity to an image.
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Digitisation. The process of converting analogue information into digital for use by a computer.
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Dioptre Adjustment. This adjusts the optical viewfinder's magnification factor to suit the eyesight of the cameras user. There should be a knob or dial near the viewfinders eyepiece, however, not all cameras have this feature.
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DOF. Abbreviation of Depth of Field.
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Download. Term used for the transference of image data from the camera to your computer. Can be done via a serial port or the faster USB port. Downloads can also be done via Bluetooth or Infra-red without the need for cables.
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DPI. Dots per Inch. This is a measurement value used to describe the resolution of a display screen or that of a printer
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DPOF. Digital Print Order Format. This allows you to embed printing information on your memory card. You just select the photographs that you want printed and how many prints to be made. Some photo printers such as Pictbridge use this information at print time.
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DSLR. Digital Single Lens Reflex (SLR). Camera with interchangeable lens.
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Dye Sub. Dye sublimination is a printing process where the color dyes are thermally transferred to the printing media. The printers use CMYK color format. The paper is run in and out of the printer 4 times, once for each color (C, M and Y) and a fourth time when a protective overcoat is applied. Dye sub is continuous tone printing, it prints tiny square dots each of which is denser in the centre and lighter on the edges. The dyes are transparent so different colored dots can be printed on top of each other to form any one of 16 million colors.
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Dynamic Range. This is a measurement of the accuracy of an image in color or grey level. More bits of dynamic range results in much finer gradations being preserved.

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