Glossary of Scanning and Digital Imaging Terminology

There is a great deal of technical terminology to understand as you learn about scanning your photos, slides or negatives. We have put together this glossary to serve as a reference to understand these terms.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A:

Anti-Newton Glass. Glass that is treated to reduce or eliminate newton rings. The treatment creates a very fine roughness on the glass surface, similar to anti glare or museum glass used in traditional framing. Useful in scanners where film must be held flat for scanning and hence must be in contact with the glass.

Aspect Ratio. The ratio of an image's width and height. For example, 35mm film has an aspect ratio of 3:2 (36mm x 24mm), standard TV is 4:3 and widescreen TV is 16:9.

B:

Bit Depth. A measure of the number of colors or shades of gray that can be represented by a pixel. Commonly, digital images use 8 bit representations for each of three color channels - Red, Green and Blue, or RGB. Hence these images are referred to as "24-bit color". Higher-end scanning and photo equipment may produce images with up to 16 bits per color channel, or 48-bit color. (Note that some equipment and software works with images represented by 4 color channels - see CMYK.)

Black Point. A reference point that defines the darkest part of an image. In photo editing software such as Photoshop, or in scanning software such as Vuescan, the black point can be adjusted. Compare to white point.

C:

Calibration. The act of setting hardware and software to produce images with known color and density values. In scanning, this is achieved through two techniques. The first is to assure that the images displayed on the screen are "correct" by adjusting the monitor and the computer so that they are in agreement. This is normally done with the help of a piece of hardware that is attached to the monitor to measure the light and color output. The second is to measure the behavior of the scanner by scanning a known "target" (i.e., a piece of film with known contents) and analyzing the output so that scans made with the equipment may be adjusted for the characteristics of the scanner hardware.

CCD. Charge coupled device. One of two main types of image sensors. Commonly found in flatbed and film scanners. A CCD converts light into electrical signals in order to produce a digital image.

CD. Compact Disc. A digital, optical recording media with a capacity of approximately 640MB. May be used in multiple formats: (1) to store audio for playback in standard CD players, or (2) to store data for use in a computer. Compare to DVD.

CMYK. Cyan-Magenta-Yellow-blacK. A digital image representation format where pixels are represented by 4 values, or color channels. Each color channel may be an 8 bit or 16 bit value, or bit depth. This representation is commonly used in high-end printing equipment and many publishing workflows. Contrast with RGB.

Color Channel. For RGB images, there are three color channels, Red, Green, and Blue, each expressing how bright the corresponding color is for each pixel in the image. In CMYK images, there are four color channels.

Color Profile. A color profile specifies how a device deviates from a color space. The profile provides software with a mapping from colors perceived by the device to a standard, well-defined color space definition. Software can use this mapping information to correct the color when displaying, printing or otherwise working with the image. See color space and ICC profile.

Color Management. The art and practice of assuring that colors are properly represented and displayed on all input and output devices. Good color management practices assure that printed images will match images displayed on the monitor and images from scanners or cameras will be properly displayed on both. Many hardware and software tools and techniques are used to assure this uniformity of color presentation and representation.

Color Space. A mathematical model of how color is represented. Color spaces define what colors may be displayed; color spaces may vary in "size" - the number or variety of colors that can be represented. The primary color spaces photographers use are sRGB (smallest space), AdobeRGB (medium space), and ProPhotoRGB (largest space).

Compression. In digital images or video, the act of making the digital file smaller. This reduction in size may result in the loss of some data from the image or video (i.e., a reduction in quality) if the compression algorithm that is used is "lossy". Common compression techniques used on digital images are JPEG, LZW and ZIP.

Contrast. An measure of the difference between the darkest and lightest areas of an image. Sometimes used to describe the difference in brightness between various objects in an image (e.g., foreground and background).

Cropping. The act of trimming a photo along the edge or edges to reduce it's size. Cropping may be done in a manner that retains the original aspect ratio, or it may change the aspect ratio.

D:

Depth of Field. The span of distance over which a lens can sharply focus on a subject. In scanners, this distance is rather small; hence film or photos must be held flat during scanning to achieve good focus across the entire image.

Digitize. The act of converting something (an image, sound) to digital form. Scanning is a technique to digitize film or photos.

DMax. A measurement of the darkest detail that can be scanned by a scanner while still showing visible detail in the dark areas. When scanning slides, the DMax value of the scanner is important because slides (if well shot and developed) have a high dmax value. Negative films are more forgiving.

DPI. Dots per inch. A measurement of the density of pigment on a printed or displayed image or document. This term is sometimes incorrectly used to describe the density of points that a scanner picks up from a scanned object (the term PPI, or pixels per inch should be used instead). Compare to PPI.

Drum Scanner. A high end scanning technology that uses fluid immersion (wet mounting) and photo multiplier tube scanning technologies. Provides very high resolutions. Very expensive to employ and very difficult to do well. With the prominence of digital image capture for publication, the drum scanning industry is significantly smaller than it was in past years. Compare to film scanner and flatbed scanner.

DVD. Digital Video Disk. A digital, optical recording media with a capacity of approximately 4.2GB. May be used in multiple formats: (1) to store video for playback in standard DVD players (i.e., the kind you attach to your TV), or (2) to store data for use in a computer. Compare to CD.

Dry Mount. Scanning film without immersing it in a fluid. This is the standard method used by consumer flatbed and film scanners, as well as mid- and high- end film scanners. Compare to wet mount.

E:

F:

File Formats. A standard that defines the meaning of the data in a file. With regards to digital images, see TIFF, JPEG, PNG and GIF.

Film Scanner. A scanner designed and constructed to scan film only. The optics and transport hardware, as well as the image sensor and supporting electronics are optimized to scan film, not documents or other materials. This results in higher quality scans compared to a flatbed scanner. Compared to a drum scanner, results are not as good, but costs are very significantly less. Compare to flatbed scanner and drum scanner.

Flatbed Scanner. A scanner with a flat glass bed for scanning documents. Some flatbed scanners include a transparency adapter with allows for the scanning of film by shining light through the film during scanning. Results for scanning film with flatbed scanners are generally mediocre. Compare to film scanner and drum scanner.

G:

Gamma. a measurement of the midtone contrast in an image or on a display. Changes in gamma values (e.g., using the levels tool in Photoshop) will affect the balance of the midtones, but does not effect on pure white or black.

Gamut. The range of colors that may be represented by a particular color space. Some color spaces can represent a large range of colors and are therefore called wide-gamut. Also refers to the range of colors that an output device can produce.

GEM. GEM is the brand name of a software program developed by Kodak for reducing the effect of grain and noise in digital images.

GIF. A digital image file format. It is commonly used for small graphic images on the Internet. It is rarely used for larger photographs. 8-bit per pixel, 256 colors in a lossless compressed format. Compare to TIFF, JPEG, and PNG.

H:

Highlight. The brightest, or lightest parts of an image. Compare to shadow.

Histogram. A graphical representation of the tones from shadows (darks) to highlights (lights) in an image. many digital cameras and most image editing software will display a histogram (usually with representations of each color channel) to allow the user to judge the exposure, contrast, and color balance characteristics of the image.

I:

ICC Profile. A standardized representation of the meaning of the data values in a digital image. An ICC profile contains both a color space and a color profile representation. An ICC profile is used by the computer to display the colors in the image properly by adjusting the values displayed according to the profile.

ICE. ICE is the brand name of the software and hardware developed by Kodak to reduce the effect of dust and scratches in scanned images.

Image Size. A measurement of the dimensions in pixels of a digital image. This should not be confused with file size - the measurement of the size of a file in bytes/kilobytes/megabytes.

Interpolation. The act of changing resolution of an image in a way which requires the software to estimate the value of pixels in the resulting image. In some cases, this results in inaccuracies in the resulting image.

J:

JPEG. A digital image file format. It is commonly used for images on the web and from digital cameras. It is a compressed file format; the level of compression can be adjusted to trade off image quality for file size. See TIFF, PNG and GIF.

K:

L:

Lossless Compression. One of the many compression algorithms that reduces file size without any loss of data. That is, the original file can be reproduced exactly from the compressed file. Common lossless compression algorithms used on image files include LZW and ZIP. Compare to lossy compression.

Lossy Compression. One of the many compression algorithms that reduces file size with the effect of losing some data in the file. That is, the original file can not be reproduced exactly from the compressed file. The common image file format using a lossy compression algorithm is JPEG. Compare to lossless compression.

LZW. A lossless compression algorithm commonly used with TIFF files. LZW is an acronym based on the names of the inventors: Lempel, Ziv and Welch. This algorithm is designed to be fast but may not achieve the most compression possible. Compare to ZIP.

M:

Metadata. Extra data that is embedded in a digital image file, in addition the image data. Metadata is used to annotate an image with information such as creation dates, copyright information, locations, etc. Metadata is usually embedded using two standard data formats - EXIF and IPTC. Most photo software can read and write this data.

Midtones. The tones in an image that are between the dark and bright values. Some definitions of the term place numerical constraints on the values included in the midtones "bucket". However, there is no standardized definition.

N:

Newton Ring. An effect seen when film is scanned when it is in contact with standard glass. It appears as concentric rings around the point of contact. The effect is undesirable. It can be reduced through the use of anti-newton glass.

Nikon 5000 ED. The current 35mm film scanner from Nikon. Capable of scanning at 4000 PPI. Can scan 35mm slides, 35mm negatives and APS film.

Nikon 9000 ED. The current medium format film scanner from Nikon. Capable of scanning at 4000 PPI. Can scan 120 format film, as well as 35mm slides, 35mm negatives and a host of other formats (narrower than 60mm) with appropriate adapters.

Nikon Scan. A software package to scan images from Nikon film scanners. Delivered with all Nikon scanners. Compare to Vuescan and Silverfast.

Noise. Noise is an unwanted signal characteristic of electronic circuits. This noise comes from many different electronic effects, including thermal noise and manufacturing quality issues and semiconductor defects. In digital imaging, including scanning, noise is evident in random color variations seen primarily in areas of uniform color (such as a blue sky) or very dark areas (for slides) or light areas (for negatives). Film grain can tend to make noise more apparent. Several techniques exist for reducing noise in scanned images, including multiple pass scanning and noise reduction software such as, for example, Noise Ninja or GEM.

O:

Optical Resolution. The physical resolution at which a scanner can capture an image. This may be less than the stated resolution of the scanner, especially in flatbed scanners which commonly employ interpolation to provide the illusion of much higher resolutions. Additionally, the presence of a high-resolution sensor does not necessarily mean that the optics and mechanical structures of the scanner can provide the resolution that the sensor is capable of producing. Again, many flatbed scanners have these issues.

P:

Pixel. The representation, in a digital image, of a single point of light and color. Commonly, a pixel is represented by three 8-bit values, one each for the red, green and blue components of the color.

Photoshop. A digital image editing software package from Adobe. The most commonly used such software. Available in full (Photoshop CS3) and reduced functionality (Photoshop Elements) versions.

Posterization. A banding effect that may be seen after some edits of digital images, particularly in areas of roughly uniform color, or very gradual color gradation (such as a blue sky which gets slightly darker as it approaches the horizon). Higher bit-depth images (i.e., 16-bit scans) can help to avoid this problem. It is rarely a problem for minor edits on well scanned images even for 8-bit pixel values.

PNG. An open source, lossless compressed digital image file format. Used widely on the web, but rarely for digital images from cameras of scanners. Compare to TIFF, JPEG, and GIF.

PPI. Pixels-per-inch. A measurement of the density of samples in a scanned image. Modern film scanners resolve from 2000-6000 PPI. The commonly used Nikon film scanners at 4000 PPI. Compare to DPI.

Q:

R:

Resolution. Generally, a measurement of the number of pixels that make up an image. The higher the number of pixels in an image, the higher the resolution, and the larger the file size. In scanning, sometimes used to refer to the scanning PPI of the scanner.

RGB. A digital image representation format that uses three color channels, Red, Green and Blue, to represent each pixel. Each color channel may be an 8 bit or 16 bit value, or bit depth. RGB is the common image format for most digital cameras, as well as images on the web. Compare to CMYK.

ROC. ROC is the brand name of a software program developed by Kodak for reducing the effect of color shifts caused by fading in scanned images from film or print. It can be amazingly effective for some faded images.

Rotation. Transforming digital image data to skew the image, most often in 90° increments. Rotations in 90° can be done lossless (without image degradation) for all file formats.

S:

Saturation. The extent to which one or two of the three RGB color channels (or one, two of the C, M, of Y channels in CMYK color channels) predominate in a pixel. As color channel values equalize (approach the same value), a pixel's color becomes desaturated -- more gray, white or black, depending on the value of the channels.

Sepia. In traditional photo printing, a gold toning bath can produce a reddish-brown color in the print, referred to as sepia. This can be emulated in digital photography.

Scanner. A piece of hardware for capturing images from film, print or paper. Types of scanners include film, flatbed and drum scanners.

Shadow. The dark parts of an image. Compare to highlight.

Sharpening. The process of increasing the contrast at specific points in an image where lighter and darker areas touch. Lines, edges, and other details in an image can be excentuated or exaggerated through sharpening producing the effect of focusing the image.

Silverfast. A commercial software package to scan images from flatbed and film scanners. Compare to Vuescan and Nikon Scan.

T:

TIFF. A digital image file format. TIF files can be uncompressed, or compressed using LZW or ZIP compression algorithms. Commonly used for higher end photo applications where the artifacts from JPEG compression are to be avoided. Compare to JPEG, PNG and GIF.

Transparency Adapter. Some flatbed scanners include a transparency adapter, which allows for the scanning of film by shining light through the film during scanning. In many cases this "adapter" is built into the lid of the scanner; only a cover needs to be removed to expose the area containing the light used to shine through the film.

TWAIN. A standard for acquiring images from image scanners, allowing scanning an image directly into the application (such as Photoshop). For some workflows, this is an important optimization.

U:

Unsharp Mask. A common sharpening technique that first blurs an image then subtracts the original image from the blurred image to yield a image of enhanced sharpness. Sounds like magic, but it is a basic filter theory that embodies a high frequency filter that accentuates edges. Used conservatively, this technique works very well on scanned images; used too aggressively it may unwanted introduce image artifacts.

V:

Vuescan. A widely used, commercial software package to scan images from flatbed and film scanners. Compare to Silverfast and Nikon Scan.

W:

Wet Mount. Scanning film by immersing it in a fluid. This is the standard method used by drum scanners. The fluids used are very volatile and the technique is quite difficult to do well. Compare to dry mount.

White Balance. (Alternatively, color balance, neutral balance.) Adjustment of the relative amounts of individual color channels such that neutral (gray) colors are reproduced correctly.

White Point. A reference point that defines the brightest part of an image. In photo editing software such as Photoshop, or in scanning software such as Vuescan, the white point may be adjusted. Compare to black point.

Workflow. A defined process by which a goal is attained In digital imaging, usually refers to the processes of acquiring, adjusting and outputting images (and all the minor steps to achieve these goals). An efficient, high quality workflow takes a great deal of experience and effort to develop.

X:

Y:

Z:

Zip. A lossless data compression method used regularly with digital images, particularly those in TIFF format. Compare to LZW.