Definition of Terms used in Digital Imaging.
Anti-Aliasing Filter
Also called a low pass optical filter. Blurs light slightly as it passes through. Prevents moire pattern caused by the regular pattern in the sensor interacting with a regular pattern present in the subject being photographed. (Like a window screen.)
Aperture
The opening through which light passes when the camera shutter release is triggered. The aperture is designed so the size of the opening can be altered. The aperture size controls depth of field. A small aperture results in a large depth of field, a large aperture results in a shallow depth of field.
Aspheric Lens
Glass element that does not spherical profile. Used to address spherical aberration. (A lens assembly that contains an aspheric lens may be referred to as an aspherical lens.)
Blown Highlights
Areas that have been overexposed so that the area is rendered as pure white. All details in the area have been lost.
BMP
Bitmap. Microsoft's raster image file format. Usually no compression involved when this format is used.
Bokeh
From the Japanese word boke meaning "blur" or "haze". Refers to how a lens renders out of focus objects. Bokeh can add or detract from image aesthetics.
CCD
Charge coupled device. Term describing one of the two technologies used by image sensors found in digital cameras.
Clipping
Loss of detail due to over or under exposure.
CMOS
Complementary metal oxide semiconductor. Term describing one of the two technologies used by image sensors found in digital cameras.
Color Temperature
Numerical description of a light source based on the light produced by an incandescent black body. The value assigned is based on the temperature to which the black body has to be heated to produce a light that matches the light source in question.
Color Rendering Index
Sun light and incandescent light sources produce light across all wavelengths. Other sources fail to emit certain wavelengths. The CRI provides information on how much of the visible spectrum is produced by an artificial light source. (A CRI of 95 is close to full spectrum.)
Depth of Field
The area of an image (front to back) that appears to be in focus. A shallow depth of field helps isolate the subject by blurring objects in front of and behind the subject.
Diffusor
Object used to scatter light from a strong light source. This softens the shadows cast by the photographer's subject.
DSLR
Digital Single Lens Reflex. SLR camera that uses an electronic sensor in place of film. Information is stored in a digital format, usually on a storage card.
F-Stop
Description of the aperture size in comparison to the lens's focal length. (Numbers treated this way are known as ratios and can be written as fractions. The f-stop number would be the divisor. This means the aperture at f-2 is larger than f-3. 1/2 is larger than 1/3.) Depth of field increases along with the f-stop number.
Full-Frame
Describes a digital camera sensor that is the same size as a 35mm negative. Cameras with full-frame sensors can use lenses designed for film SLR cameras with no impact on image output,
GIF
Graphics Interchange Format. Image file format developed by CompuServe. Limited to 256 color palette. Supports animation. Uses lossless compression method. Not suited for photographs but well suited for web graphics and computer games.
Grain
Term related to film photography. Grain occurs when the individual granules used by the film to capture light become apparent in the end product. This effect is sometimes desired and can be replicated when using digital photography.
ILC
Acronym for Interchangeable Lens Camera. Cameras with removable lenses. This makes the camera more versatile as the lens can be changed for best results.
ISO
Number used to measure film's light sensitivity. Light sensitivity increases along with the ISO number. Higher ISO films can take pictures under lower light conditions, but the amount of grain increases. The ISO number has been adopted for digital sensors. The sensor's light sensitivity can be altered simply by changing a setting on the camera.
JPEG
Compression method used when saving image data. Lossy method that will effect image quality. More compression equates to more quality lost. File formats that use JPEG compression include .jpg, .jpeg, .jpe, .jfif and .jif. Digital cameras often save files in one of these formats. (Sometimes the only format offered.)
Image Sensor
Chip in a digital camera or camcorder responsible for converting light into an electrical charge that is then used to create a digital image. The sensor size has an impact on image quality. Bigger is better when it comes to image sensors.
Lens
In photography, "lens" is used to describe the device used to focus light on the image sensor or film. These actually contain multiple glass glass elements. (Technically, each element is a lens and the entire device is better described as a lens assembly but nobody actually does that.)
Low Pass Filter
See Anti-Aliasing Filter
Macro
Strictly defined, refers to the ability to focus close enough to a subject to render it life sized on the image sensor. Usually loosely used to refer to extreme closeups.
Memory Card
Storage device used by digital cameras. Comes in multiple sizes. Compact flash (CF) is the largest and primarily used in large format (professional) cameras. Secure Digital (SD) and Micro SD are usually the type used by consumer digital cameras.
Metadata
Defined as data that describes other data. In digital photography, metadata is the information saved by the camera along with the actual image. This information can include date, time, ISO setting, f-stop setting and any exposure adjustment.
MILC
Mirror-less Interchangeable Lens Camera. Camera that does not include the mirror used by SLR cameras. Framing image is usually done with electronic viewfinder or with LCD screen. Removing mirror allows for shallower body design and lighter camera.
Moire
Artificial pattern that occurs in an image. Caused by the regular pattern used in the camera's color filter interacting with a regular pattern present in the image when the picture was take. Addressed by using a low-pass optical filter or anti-aliasing filter.
Neutral Density Filter
Glass filter placed over the camera lens. Used to reduce the amount of light entering the camera without affecting color. This increases exposure time. Useful for creating artistic motion blue effects.
Noise
Improperly rendered pixel(s). Pixel or group of pixels may be too bright, too dark or wrong color. This causes a distracting spot on image. Small amounts of noise may only be visible when image is viewed at larger sizes.
Pixel
An individual dot used to create an image. Rendered as a square when magnified on a computer screen.
PNG
Portable Network Graphics. Image format designed to replace GIF. Uses a lossless compression algorithm. Supports palette-based images (like GIF) and full-color RGBa images. Supports transparency settings. Well suited for web graphics. (Old browsers may not support.) No native support of animation.
Polarizing Filter
Filter that blocks light with a certain orientation. Can effect the color of the sky or alter the appearance of reflections.
Prime Lens
Camera lens with fixed focal length. Opposite of a zoom lens. (Can also refer to the primary lens when multiple lenses or optical devices are used at the same time.)
RAW
File format used to save minimally processed data from image source, including digital cameras. File must be processed before it can be printed. The file extension depends on the manufacturer of the device used.
Resolution
Resolution refers to amount of detail in an image. Expressed in pixels-per-inch for images viewed on a computer screen and dots-per-inch when printed. (Monitors usually have a resolution of 72 ppi, printers usual print at 300 dpi. An image will be much smaller when printed than when viewed onscreen due to the resolution difference.)
Rule of Thirds
Composition guideline. Divide an image into three horizontally and vertically. The Rule of Thirds holds that the focus of interest is best placed where one of the areas where the horizontal and vertical dissecting lines meet. (Also holds the horizon line is best placed at the 1/3 of 2/3 mark.) Developed by John Thomas Smith.
Shutter speed
The amount of time the aperture is open. (Some digital cameras don't have an actually shutter. In these cameras the "shutter speed" is the amount of time over which the sensor collects data.)
SLR
Camera designed so the view-finder shows an image seen through the camera's lens. Historically done by placing a mirror in front of the film or sensor.
Spherical Aberration
Optical effect caused by light bending more at the lens outer edge than at its center. The light rays do not strike the film or sensor at the same point, causing parts of the image to be out of focus or other image defects.
TIF/TIFF
Tag or Tagged Image File Format. File format for storing images. Patent currently owned by Adobe. Widely supported flexible format. Many RAW file formats are modified TIFF files.
Vignette
Image where the edges are darker or lighter than the rest of the image. Helps draw the viewer into the image. Can be natural effect or the result of image editing.
Zoom Lens
Camera lens with variable focal length.
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