Photographic Glossary-D

D/log E curve
A graph of density (D) against the logarithm of exposure (log E) Used in sensitometry to compare the sensitivity of different emulsions to light.

The CIE Standard Illuminant that represents a colour temperature of 5000 K. This is the colour temperature that is most widely used in graphic arts industry viewing booths.

The CIE Standard Illuminant that represents a colour temperature of 6504 K.

An early photographic process (invented in 1839) where the impression made on a light-sensitive silver-coated metal plate is developed by mercury vapor. Each is an original since no duplication process exists.

Material used to cover the photographer's head and camera to block surrounding light in order to better view the image on the camera's ground glass viewing screen.

A light tight area used for processing films and for printing and processing papers; also for loading and unloading film holders and some cameras. For image purist, the cycle of photograph is not complete if the darkroom process is not handled personally.
A room or small area that can be made completely lightproof, so it can be used for working with photographic film, paper, or other light-sensitive materials.

Many medium and large format cameras allow for the "backs" to be switched midroll to allow for varying films to be used. In order to change backs a dark slide is placed between the film and the outside world preventing fogging of the film.

Data compression
Digital cameras don't have the massive amounts of storage a computer does, yet they create files that can be quite large. Because of this, the camera compresses used, the better the image. The more compression used, the more images can be stored.

Data Disk
A circular, rotating disk at the end of Advanced Photo System film cassettes that functions as a circular bar code, communicating the film speed, type and exposure length through a sequence of reflective bars to an optical sensor in the camera.

The number that make up a digital file.

A database is a collection of data that is organized so that its contents can easily be accessed, managed, and updated.

Daylight Balance
Most film available on the market today is Daylight Balanced. Unless the film specifically states that it is balanced for other lighting conditions, it will probably be designed for daylight. This film will produce natural colors when exposed under natural (outdoors) conditions or under normal flash. When shot under tungsten lighting (incandescent light bulbs) there will be a reddish yellow tint to the photo and when shot under fluorescent lighting there will be a green hue.

Daylight film
Film balance to give correct rendition when shooting under average daylight and flash illumination, approximately 5500K.

DC (Defocus Image control)
A new type of lens family introduced by Nikon, designated as DC lens. Mainly for portrait photography. The lens enables to control background and foreground blur precisely, resulting in strikingly attractive portraits.

When a image or other digital data set is compressed and stored, it is not usable until it is decompressed into it's original form.

Dedicated Flash
A fully automatic flash that works only with specific cameras. Dedicated flash units automatically set the proper flash sync speed and lens aperture, and electronic sensors within the camera automatically control exposure by regulating the amount of light from the flash. A simple glance can differentiate by identifying the multiple contacts on the hot shoe (the place where the flash is mounted). Electronic flash that must be used with specific cameras to automatically adjust the camera's exposure controls to produce the correct exposure.

The setting in a computer program which will take effect if no change are made.

Sharpness of an image ( as seen by the clarity of detail ) formed by an optical system. The clarity of detail in a photograph.

Blends the pixels along the edge of a selection to seamlessly merge it with a new background.

Process of eliminating magnetism, such as with a colour monitor face plate, to eliminate distortion.

Delayed action
Mechanism delaying the opening of the shutter for some seconds after the release has been operated. Also known as self-timer.

The distance between two colours in the CIELAB colour space, used to indicate colour differences and to establish quantitative colour tolerances.

Describes a negative or an area of a negative in which a large amount of silver has been deposited. A dense negative transmits relatively little light.

An electronic device for measuring the amount of light transmitted through or reflected from a sample, such as the gray percentage values in halftone films. An instrument used for measuring the optical density of an area in a negative or print.

The ability of a negative to allow light to transmit through it is a function of the density of the negative. This is based on the density of silver oxide in the negative causing light to not be able to transmit through a negative. A very dense negative will be very light and lacking detail when printed. The blackness of an area in a negative or print that determines the amount of light that will pass through it or reflect from it. Sometimes referred to as contrast. The relative amount of silver in various areas of film or paper after exposure or development therefore the darkness of a photographic print or the light-stopping ability of a negative or transparency.

Depth Of Field Preview
Some cameras contain a button or lever that, when depressed, will "stop down" a lens to the aperture set to allow the user to see the depth of field that will be seen in the photo at that aperture setting. Most focusing is done with the lens open, or at the lowest aperture setting possible. Focusing is done easier at this stage. Many of the automatic SLR cameras today do not have the DOF preview feature while many of the older manual cameras do have it.

Depth of field scale
Scale on a lens barrel showing the near and far limits of depth of field possible when the lens is set at any particular focus and aperture.

Depth of Field
The zone of acceptable sharpness in front of and behind the subject on which the lens is focused; extends approx. one-third in front of and two thirds behind the in-focus subject; dependent on three factors: aperture, focal length, and focused distance; the wider the aperture, the longer the focal length, and the closer the focused distance, the less the depth of field, and vice versa; in comparison to a normal lens, wideangle lenses have inherently more depth of field at each f-number and telephoto lenses have less. Since this element is very important, another simpler way to explain is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. Depth of field depends on the lens opening, the focal length of the lens, and the distance from the lens to the subject or can explain as in simpler term as the zone of sharpest focus in front of, behind, and around the subject on which the lens is focused; can be previewed in the camera - very handy for critical work.

Depth of focus
Depth of focus refers to the zone in front of and behind the focal plane in which the blurred image point is smaller than the acceptable circle of confusion. An image, if it is not on the focal plane but within the depth of focus, is distinguished as a sharp image although it is, in fact, slightly blurred. Depth of focus depends on the f-number and the acceptable circle of confusion. The focal length of the lens does not affect the depth of focus. The distance range over which the film could be shifted at the film plane inside the camera and still have the subject appear in sharp focus; often misused to mean depth of field. Also see "depth of field" section.

Derived Image (Derivative Image)
An image that has been created from another image through some kind of automated process, usually involving a loss of information. Techniques used to create derived images include sampling to a lower resolution, using lossy compression techniques, or altering an image using image processing techniques.

Removal of halftone dot patterns during or after scanning printed matter by defocusing the image. This avoid moiré patterning and colour shifts during subsequent halftone reprinting.

Straightening an image that as been scanned crookedly, or straightening type that is slanted.

To remove or reduce speckles or dust spots introduced during scanning or image processing.

a click stop in the shutter release button, a place where the mechanism is designed to register specific information such as exposure or focus before the button is fully depressed.

A solution containing a number of chemicals that will convert a latent image on a exposed photographic material to a visible image. A solution used to make visible the image produced by allowing light to fall on the light-sensitive material. The basic constituent is a developing agent which reduces the light-struck silver halide to metallic silver. Colour developers include chemicals which produce coloured dyes coincidentally with reduction of the silver halides.

Developing Tank
A light tight container used for processing film, a darkroom's essential accessory. A light-tight container, made of plastic or steel, in which film is developed. The exposed film is loaded into the tank in complete darkness, and temperature controlled chemicals are added at precisely timed intervals to make the image and stable.

1. The entire process by which exposed film or paper is treated with various chemicals to make an image that is visible and permanent.
2. Specifically, the step in which film or paper is immersed in developer.

Device driver
Software that tells the computer how to communicate with a peripheral device, i.e. printer, CD-ROM.

Device profile
A representation, in the CIE model, of the colour rendering characteristics of any input, display or output device.

Describes a colour space that can be defined only by using information on the colour-rendering capabilities of a specific device.

Describes a colour space that can be defined using the full gamut of human vision, as defined by a standard observer, independent of the colour- rendering capabilities of any specific device.

An adjustable device inside the lens which is similar to the iris in the human eye; comprised of six or seven overlapping metal blades; continuously adjustable from "wide open" to "stopped down"; controls the amount of light allowed to pass through the lens and expose the film when a picture is taken; a]so controls the amount of depth of field the photograph will have; in lenses designed for single-lens reflex cameras, there are basically two types of diaphragms: Lens opening. A perforated plate or adjustable opening mounted behind or between the elements of a lens used to control the amount of light that reaches the film. Openings are usually calibrated in f-numbers. The more blades used will have a more natural and rounded spots.
There are two types of diaphragms:
Automatic: The most popular type; controlled by a single aperture ring; during viewing and focusing, the diaphragm remains wide open, allowing the maximum amount of light to go to the viewfinder for a bright and easy-to-focus image; at the instant of exposure, it stops down automatically to a particular aperture and then reopens to full aperture immediately afterward.
Manual Preset: Used in some specific lenses like, PC-Nikkor lenses for Nikon for instance; controlled by two separate rings; the preset ring is first set to the desired aperture, then the aperture ring is rotated to stop down the diaphragm manually for metering or prior to taking pictures. The part of the camera that governs the size of the aperture. The most common type is the iris diaphragm- a system of curved, overlapping metal blades that form a roughly circular opening similar to the iris of the eye. It varies in size to control the amount of light.

Dichroic head
An enlarger head that contains yellow, magenta, and cyan filters that can be moved in calibrated stages into or out of the light beam to change the colour balance of the enlarging light.

Diffraction filter
A colourless filter inscribed with a network of parallel grooves. These break white light up into its component colours, giving a prism-like effect to highlights.

When light is obstructed by an object and the wave front is changed, interference occurs between components of the altered wave front. The pattern formed by interference is called the diffraction pattern. Many components are designed to yield very specific diffraction effects (diffractive optics, gratings). Other components attempt to counteract this process to determine more information about the obstructing medium (electronic imaging).

Diffuse Lighting
Lighting that is low or moderate in contrast, such as on an overcast day. Light that has lost some intensity by being reflected or by passing through a translucent material. Diffusion softens light, eliminating both glare and harsh shadows, and thus can be of great value in photography, notably in portraiture.

A material that softens light passing through it. The effect is to soften the character of light. The closer a diffuser is to a light source the less it scatters light. Softening detail in a print with a diffusion disk or other material that scatters light.

Diffusion disk
A flat glass with a pattern of lines or concentric rings that breaks up and scatters light from an enlarger or camera lens and softens detail in a photograph.

Diffusion enlarger
An enlarger that illuminates the negative by scattering light from many angles evenly over the surface of the negative. detail is not as sharp as with a condenser enlarger; negative blemishes are minimized. An enlarger that scatters light before it strikes the negative, distributing light evenly on the negative. Detail is not as sharp as with a condenser enlarger; negative blemishes are minimised.

Diffusion-Condenser Enlarger
An enlarger that combines diffuse light with a condenser system, producing more contrast and sharper detail than a diffusion enlarger but less contrast and blemish emphasis than a condenser enlarger.

Digital camera
Instead of using film, this kind of camera records data in "pixels," small squares of light of varying hues that can be directly loaded into and interpreted by a computer.

Digital Duplicates
Reproductions of an image that are produced by scanning the original analog image to produce a digital image file, and then imaging the digital file using some variety of digital printing or recording device.

Digital envelope
A digital "container" that surrounds an image with information (or metadata) in a file. Such information might be used to find the image, guarantee its authenticity, or limit access to authorized users. An envelope adds additional "overhead" to a file in excess of the actual "data" of an image.

Digital film
The analogous component in digital cameras to film in optical cameras. This usually consists of some type of semiconductor memory, with or without additional components, usually in the physical form of a removable cartridge.

Digital Halftone
The use of fine pixels to create the halftone pattern that is then written to film, direct-to-plate or direct-to-press for printing.

Digital- image filtering
Processing on an image performed by combining or comparing individual pixels with their neighbors. Many interesting and useful effects can be obtained, such as sharpening, blurring, edge detection, and embossing.

Digital imaging
A method of image editing in which a picture is recorded as digital information that can be read and manipulated by a computer, and subsequently reformed as a visible image.

Digital internegatives
Internegs that are produced by digitally scanning the original transparency to create a digital file, and then imaging the digital data using a film recorder to record the image onto a negative film stock.

Digital printer
A printing device that is capable of translating digital data into hardcopy output.

Digital Signal Processors (DSP)
Microprocessor chips specially designed to convert, modify and manipulate streams of digitized signals in real time. These chips allow for faster telephony, faxing, and audio and video capture and editing.

Digital Zoom
Rather different from Optical Zoom.  With Digital Zoom the image is magnified by spacing out the pixels electronically, and as such is really very little different from blowing an image up to a larger size using a software package on your PC.  Digital Zoom has a detrimental effect on image quality, so depending on your application, you need to be careful how you use it.  

A system whereby information is represented by binary digits, or "bits." Binary information has two states, "0" and "1,"or "on" and "off," and can thus be easily processed by electronic systems. Analog information can be converted to and from digital information via devices called "Analog to Digital Converters" or "Digital to Analog Converters." Digital information does not suffer from the degradation and noise problems prevalent in analog circuits.

Digitizing tablet
A mouse replacement comprised of a "pen" and flat panel wired to the computer. Pen movements on the tablet are reproduced on the computer screen and pressing the tip of the pen against the tablet mimics pressing the mouse button. Some tablets may be pressure-sensitive in illustration programs like Photoshop -- a harder pressure makes a thicker line. Wacom brand pressure-sensitive tablets are favored over the mouse by many graphic artists.

To convert an image into binary code. Visual images are digitized by scanning them and assigning a binary code to the resulting vector graphic or bit-mapped image data.

Is the reduction in the strength of a liquid by mixing it with an appropriate quantity of water.

Deutche Industrie Norm (Film speed rating defined by the Deutscher Normenausschuss (German standards organisation).). Numeric rating used to describe emulsion speed for German Made photosensitive materials. Just as the same as ASA and ISO numbers.

Light sensitive electronic components used in image capture. They function as one-way valves that sense the presence or absence of light and create a digital signal that the computer converts into pixels values.

Diopter correction
This is like a focus adjustment that matches the focus of the camera's optical viewfinder to the user's eyesight. This way, users don't have to wear their glasses when using the camera. As some of the viewfinders are quite small and difficult to use with your glasses on diopter correction can be a welcome option for eyeglass wearers.

Optical term for the power of a lens. Photographically, it is typically used to indicate the magnification and focal length of close-up lenses.

Direct light
Light shining directly on the subject and producing strong highlights and deep shadows.

Direct Memory Access
The ability to use memory without a software interface.

Direct photo printing
A feature of some photo printers that allows users to transfer a memory card from a camera directly to a printer, enabling the images on that card to be printed without a PC.

Direct positive print
Made from a transparency without an internegative on a direct positive colour paper. A high contrast positive image slide made only from camera ready originals with no negative required.

Directory folder
In a graphical user interface, an icon resembling a yellow file folder where other files are stored for data organization. Directory folders are used to represent any drive or directory contents in the system.

The spelling variation of "disk" referring to compact discs such as Photo CD or other CD-ROM.

Disk drive
A device that can contain a fixed or removable spinning disk used for storage of digital data.

Light rays of different wavelengths deviate different amounts through a lens causing a rainbow effect around points and edges. The property of materials which have a refractive index that varies according to the wavelength of light, i.e., bend the rays of some colors more than others; a prism placed in the path of a ray of white light bends the blue and violet rays more than the orange and red, so that it spreads out or "disperses" the colors as a continuous spectrum.

Display technology
The type of technology used for desktop displays, such as CRT (cathode ray tube) or LCD (liquid crystal display). Other forms of display technology include LED (light-emitting diode) and gas plasma.

A phenomenon in which straight lines are not rendered perfectly straight in a picture. There are two types of distortion--barrel distortion and pincushion distortion. Distortion cannot be improved by stopping down the lens. Even if the other possible aberrations were totally eliminated, images could result that still have a distorted appearance. For an example, an rectangle may appear as a barrel or pin cushion-shaped object. A lens aberration which does not affect the sharpness of the image, but alters the shape of objects; the inability of a lens to render straight lines perfectly straight; does not improve by stopping down the lens; there are two types of distortion
Barrel: Straight lines are bowed in at the edges of the picture frame resembling the sides of a barrel; present in small amounts in some wideangle or wideangle-zoom lenses, but uncorrected in fisheye lenses.
Pincushion: The opposite of barrel distortion; straight lines are bowed in toward the middle to resemble the sides of a pincushion; present in small amounts in some telephoto and telephoto-zoom lenses.

Altering the values of adjacent dots or pixels on a digital output device to create the appearance of a increased number of tonal values or colours.

Diverging lens
A lens which causes rays of light coming from the subject to bend away from the optical axis.

DMA (Direct Memory Access)
Allows the I/O subsystem to access main memory for the transfer of data.

Maximum density. The greatest density in an image. Also, the greatest density possible for a particular film or paper.

Minimum density. The smallest density in a image. Also, the smallest density possible for a particular film or paper.

Dodge ( Dodging )
In photographic printing, to dodge a print is to reduce the exposure in a section of the image to make that area lighter. Compare this to the technique of burning. Holding back the image-forming light from a part of the image projected on an enlarger easel during part of the basic exposure time to make that area of the print lighter.

An area of a network over which administrative control is exercised. The primary domain is the file server for all clients.

DOS ( Disk Operating System)
The main system software that tells your computer how to work.

Dot gain
A printing defect in which dots prints larger than intended, causing darker colours or tones.

Dot pitch
The distance between the dots on a computer monitor, typically 0.2 to 0.3 millimeters. The closer the dots the sharper the image on the monitor.

The smallest raster element of an image. Many dots together produce one pixel. Meaning, for example, that in the specification "8 bit depth", three "layers" of 256 dots each are on top of one another to produce one pixel.

Dots per inch (dpi):
Measure of output device resolution and quality. For example, the number of pixels per inch on a display device. Measures the number of dots horizontally and vertically.

Dots, halftone
Minute, symmetrical individual subdivisions of the printing surface formed by a half-tone screen.

Double Exposure
Two pictures taken on one frame of film, or two images printed on one piece of photographic paper. Some cameras can have double exposure level depressed with multiple exposures one even with a motor drive. Two pictures taken on one frame, or two images printed on one piece of photographic paper.

The process of receiving data from another digital source.

The reduction in resolution of an image, necessitating a loss in detail.

To reduce the file size of an image, by lowering the resolution and/or reducing the square measurement of the file.

Dots per Inch. A measurement of resolution or fineness for a printer or scanner. A dot is the smallest unit that can be displayed, scanned, or printed. If a device has a resolution of 300 dpi, it means there are three hundred dots horizontally and three hundred dots vertically. The higher the number of dots per inch, The greater the amount of detail that can be present in the image. If all other image-quality factors are equal, the more dots per inch the better. However, with greater dpi, comes larger file-size and/or longer display and printing times.

Drag and drop
The process of moving text, graphics, or photos to different locations in a document.

DynamicRandomAccessMemory. A particular type of RAM that requires constant attention from the computer in order to retain data in storage.

Drive speed
The speed (RPM) That a drive mechanism rotates. Faster drive speeds allow for faster data transfer.

A software utility designed to tell a computer how to operate a external device. For instance, to operate a printer or a scanner, a computer will need a specific driver.

Drop-in-Loading (DIL)
Film cassette loading feature in all Advanced Photo System cameras that virtually eliminates film-loading problems by automatically accepting the leaderless cassette and thrusting the film forward to the first unexposed frame without any user intervention.

Drum scanner
A high-quality image-capture device. The image to be capture is wrapped around a drum that spins very fast while a light source scans across it to capture a digital version of the image.

Dry mounting tissue
A thin paper coated with adhesive on both sides for permanently adhering a photograph to a support. The adhesive is softened by heat and hardens when it cools.

Drying cabinet
Is a vented cabinet equipped with suspension clips for drying films.

Drying marks
Are marks on the film emulsion caused by uneven drying and resulting in areas of uneven density, which may show up in the final print.

DSP (Digital Signal Processor)
Chips that are designed to facilitate digital video and audio, along with accelerating image processing.

D-type AF Nikkor lenses (Only apply to Nikon)
AF Nikkor lenses that send Distance Information to some of Nikon's top cameras, Used for 3D Color Matrix Metering or 3D Multi Sensor Balanced Fill Flash (with Nikon SB 27/SB 26/SB 25 Speedlight). Some third party lens manufacturers are catching up to supply with compatible functions lenses too.

Dual processors
Two central processing units in the computer.

A copy of a slide or transparency made without an internegative or special duplicating film. Frequently used as an intermediate image for other print subjects.

The ability of a scanner to scan both sides of a sheet simultaneously. Requires two scanner cameras and often two processing boards.

" Digital Video Disk " An optical storage medium that can store up to 4.7 Gigabytes ( single layer ), 8.5 GB (double layer ), 9.4 GB (double sided, single layer ), or 17 GB (double sided, double layer ). Transfer rates and seek times are similar to those of CD-ROM for currently available drives. The DVD spec included higher level specs for audio and video capabilities.

DX Data Exchange
Electrical coding system employed in 35 mm format film that communicates film speed, type and exposure length to the camera.

Digital Index. Coding on the film cartridges used to transmit information in relation to film speed, the length of film and the exposure latitude to the camera. Most films - except some technical films are DX coded - means you need not to worry about wrong setting of the ISO setting of film speed anymore, reducing chances of mistakes. Common speed ISO 25 to 6400 - depends on camera models.

A checkered or bar code on some film cassettes. The checkered code can be automatically scanned by suitable equipment for such information as film processing equipment for film type, processing procedure, and so on.

Dye transfer
A method of making color prints or transparencies that gives the maximum control of color, balance and contrast. One of the most permanent color processes. This process is also known as Polaroid transfer. During the development stage of the Polaroid image the layers of the image are pulled apart to allow the colors from the chemicals to be applied to a foreign substance such as silk, wood, or other fabrics.

Dye-sublimation printer
A type of continuous tone printing process a vibrant 300ppi colour print. The pixels are printed by a thermal print heat that sublimates (vaporizes) the dye from a coloured saran wrap like ribbon onto the dye-sublimation paper. The hotter the element on the thermal printed head, the darker the spots of colour.

Dynamic range
The ability of a scanner to register a wide range of tonal values--something from near white to near black. A scanner with good dynamic range is able to map input shades correctly to output shades, making images look brighter and giving them more visible detail. Generally the number of bits determines the maximum dynamic range.