Affine Warp: A first-order spatial warping transformation, such as translation, rotation, or scaling.
Aliasing - Little jagged edges or "stair-steps" found on curves and non-vertical, non-horizontal lines in an image.
Analog - an analog signal is capable of having a continuously varying value. As opposed to digital.
Analog to Digital Converter (ADC) - a device that senses an analog signal and converts it into a proportional representation in digital form.
Artifact(ing) - Misinterpreted information from a JPEG or compressed image. color faults or line faults that have a visible negative impact on the image. Artifacting is most easily noticed on a highly compressed JPEG image.
Aspect Ratio: The ratio of an image's width to its height.
Bilevel image - another term for a binary image.
Binarization: Process which maps each pixel to one of two values based on a threshold value. For example, any pixel with an intensity above the threshold value is mapped to white and any pixel below the threshold value is mapped to black, or vice versa.
Binary Image - an image where pixel intensities take only two possible values, either zero or non-zero.
Bit - the smallest unit of digital information, having the value 0 or 1 only. The term is a contraction from ‘binary’ and ‘digit’. A binary image is a 1-bit image, whilst a grayscale image may be stored as an 8-bit image.
Bit Depth - this refers to the number of bits used to store a color. The greater the bits, the greater the colors. A pixel with 8 bits per color can display a total of 256 unique colors. 24-bit images can display over 16 million different colors.
Bitmap - the method of storing information that maps an image pixel, bit by bit. There are many bitmapped file formats, BMP, PCX, PICT, JPEG, TIFF, GIF, PNG, and so on. Most image files are bitmaps. Also known as a raster image.
Blob - a term sometimes used to describe a region of connected pixels of the same type.
Blob Labeling: The process of identifying the blobs in an image.
Blur Filter: A filter produced by replacing each pixel in an image with the average value of all of its neighbors.
Brightness Contouring: A condition caused by too little brightness resolution. Makes gradual brightness changes appear abrupt instead. For example, if you change the number of brightness levels from 16 to 8, the image will appear as if it were a "paint by number" painting or poster.
Brightness Slicing: A double contrast enhancement which produces a binary image by assigning pixels with intensity values below a lower threshold and above a higher threshold a value of black and pixels with within the upper and lower threshold ranges a value of white.
Byte - a unit of digital information, consisting of eight bits. A byte can have 256 different combinations of bits. Much computer hardware is geared to handling information in bytes. Coincidentally, in many applications, a byte is sufficient to represent the information about the gray level of a pixel.
CMYK - Cyan, Magenta, Yellow, Black. These are the printed colors typically used to create color prints. Most color printers - Ink-Jet, Laser, Dye-Sublimation, Thermal, and Crayon printers - use these as their printer colors. This is one of the color management problems for computers, since converting RGB files to CMYK files may cause unwanted color shifts. When used by a printer, CMYK is also known as reflective color since it is printed on paper or reflective films.
Compression - techniques used by imaging devices and software to reduce image storage requirements without objectionably affecting the appearance of the image.
Color Space: A means of describing a color. CMYK, RGB, and HSV are all examples of color models
Configuration File: A file that contains preferences of an application, such as language and default units used.
Contrast Enhancement: The amount of light/dark differences in the colors in an image. Zero contrast is medium gray.
Convolution: A filter calculates for each pixel a weighted average of its neighbors. The weights are stored in a kernel or convolution mask. Used to implement a common class of image processing filters, like high and low pass, and edge enhancement.
Convolution Kernel or Mask: The set of values that are used as weights for calculating the weighted average of a pixel in a convolution operation.
Digitization: The sampling of an analog signal at specific intervals to create a digital image.
Downsampling: Reducing the number of pixels in the result image by using a transformation such as scaling. For example, sampling only every other pixel in an image to produce a result image half the size of the original.
Dynamic range - the ratio between the brightest and dimmest gray level acceptable to an imaging system.
EPS - Encapsulated Postscript, a computer file standard set by Adobe Inc. for printers, which represents a mathematical definition of shapes, lines, color and space. This standard is one of the most accurate ways to define a font or image, but creates files of very considerable size. EPS files also add page description information to the files. Although forms of EPS are used on all computers, not all EPS files are the same, nor are they transferrable between programs.
Even Field: Lines 0, 2, 4, 6, etc. in an interlaced video frame.
Filter - a function which alters an image in some way, such as changing the brightness, rotating the image, etc.
Fourier Transform: Frequency space transform that decomposes a spatial image into a set of sinusoidal frequency components.
Frame Grabber: A hardware device that is capable of acquiring, storing and displaying digital images.
Frequency Domain: Domain in which an image's contents are described by the frequency of changes in intensity in the image.
GIF - Graphic Interchange Format, originally used by CompuServe for storage of graphical images in lossless compressed form. This was developed for use with images of up to 256 colors or shades (up to 8 bits) and is effective with low-noise or graphical images. This format was widely used in the late 80s for image transfer. GIF 89 is the most recent GIF standard and allows multiple images within one file, selection of area for transparency as well as other features. The primary use of this format has been on the Internet. However, it has become obsolete and the compression used is patented. A better format is PNG. For more information, go to http://burnallgifs.org/.
Gray(scale) image - an image often referred to as "black and white," although there are more colors than just black and white in it.
Gray level - the brightness associated with a region or point in an image.
Gray level histogram - in digital image processing, "histogram" refers to the distribution showing the number of pixels which have a particular intensity value.
Histogram: A statistical analysis of the number of pixels at each brightness level in an image.
Histogram Equalization: Re-mapping the intensity values in an image to balance them.
Histogram Sliding: Adding or subtracting a constant value to or from each pixel in an image to produce a lighter or darker image. (See also Offset)
Histogram Stretching: Multiplying each pixel in an image by a constant value to increase or decrease the dynamic range of the intensity values. This increases or decreases the contrast. (See also Gain)
HSI/HSL - Hue, Saturation, Intensity (or Luminance). An abbreviation for all of a color's characteristics: hue (the pigment); the saturation (the amount of pigment); and intensity (the amount of white included).
Hue - the name of a color such as red or blue.
Image arithmetic - although a digital image can be thought of as a 2-D array or "matrix" of values, mathematical equations involving images do not always follow the rules of matrix algebra. Thus, if i and j are the row and column of a particular pixel in an image A with intensity A(i,j), then the sum of images A and B, A+B is an image C where: -
C(i,j) = A(i,j) + B(i,j)
for all pixels. However the product of the two images A and B, A*B is an image C where:-
C(i,j) = A(i,j) * B(i,j)
for all pixels, rather than the formal definition of a matrix product.
Although storage of intensities in "integer" format, with discrete values, is normally adequate for representing the original image, intermediate values during calculation may fall outside the range even though the final result is still within range (e.g. during a Fourier transform). Care has to be taken with integer arithmetic to preserve precision through an arithmetic operation. In these cases floating-point arithmetic may be used.
Image processing - operations designed to enhance an image or make it more useful.
Intensity: The brightness value assigned to a pixel in a digital image.
Interlacing: A technique used in video where the odd lines are transmitted first (the odd field) and then the even lines (the even field). Used in NTSC television and in RS-170 video cameras.
Laplacian Filter: An omni-directional edge-enhancement filter.
Low-Pass Filter: A filter that emphasizes low-frequency details in an image.
Lossless compression - image and data-compression applications and algorithms, such as Huffman Encoding, that reduce the number of bits a picture would normally take up without sacrificing any image quality.
Lossy compression - methods of image compression, such as JPEG, that reduce the size of an image by sacrificing some pictorial information.
Luminance - the black and white or brightness portion of a color.
Median Filter: A filter where a pixel is assigned the median value of its neighbors.
Megabyte - 1048576 bytes or 1024 kilobytes, abbreviated as MB. It is used to refer to size of files or media such as hard drives where capacities are too great to be expressed directly in bytes or kilobytes. Refers to amount of information in a file, or how much information can be contained on a Hard Drive or Disk.
Merge: An element that combines two input images by logical or arithmetic operation into a single result image.
Monochrome image - an image displayed in shades of a single color, normally gray.
Offset: A value to be added to each pixel to increase or decrease the intensity value of all of the pixels in the image.
Pixellation - See Aliasing
Plugin - a type of program method which was first popularized by Adobe Photoshop and is now a de facto standard for all major imaging programs. Plugins allow a user to add or remove a function from a program without changing the entire program.
Pointset - a set of connected pixels which can be used to describe that feature, e.g. the boundary of a feature.
Posterization: See Brightness Contouring.
Raster Image- One method for storing an image. Information is stored as a series of pixels, sometimes compressed. See Vector.
RGB - an additive color space that forms colors by mixing various ratios of red, green, and blue. Computer monitors and digital cameras use these primary colors to create all the hues seen on the monitor and saved in files.
Saturation - designates the purity of a color. Pastels have a low saturation, for example.
Signal-to-Noise ratio (S/N ratio) - the ratio between the level of signal (or significant information) and the level of noise. Often used rather loosely to indicate the extent of information of interest as opposed to spurious detail in an image. In this context, noise is predominantly the fluctuations due to counting statistics.
Sobel Filter: An omni-directional edge detection filter which is accomplished by first adding together the results of a horizontal filter and a vertical and then taking the square roots of those values.
Square Pixel: A pixel that has an aspect ratio of 1:1 (i.e. equal dimension both horizontally and vertically). Most monitors have a 4:3 aspect ratio and and the pixels displayed in them are not square.
TIFF - Tagged Image File Format. A bitmap file format for describing and storing color and gray scale images.
TWAIN - An common interface for image acquisition developed by a group of software developers as a standard for communications between imaging devices, such as scanners and digital cameras, and the computer. TWAIN provides for easy import or acquisition of images from a range of devices into software applications that support the standard.
Computers in Microscopy, D. M. Holburn http://www-g.eng.cam.ac.uk/rms/glossary.html
Glossary, Datacube Inc. http://www.datacube.com/