1-bit image
An image comprised of pixels that contain only a single bit of information. Each pixel is either on or off. Normally, "on" is white and "off" is black.
24-bit image
A 24-bit image contains pixels made from RGB triplets.
4-bit image
An image file format that allows 4-bits per pixel. This image can contain up to 16 (24) different colors or levels of gray.
8-bit gray level
This indicates 8-bit grayscale. 8-bit gray level is used to distinguish between 8-bit indexed color (8i) and 8 bit grayscale. An 8-bit gray level DIB image is one where each pixel in the bitmap is unchanged by its palette when displayed. Each palette entry is the same as its index.8-bit image
An image where each pixel has 8-bits of information. An 8-bit pixel contains one of 256 possible values. There are two common types of 8-bit images: grayscale and indexed color.In a grayscale image, each pixel takes one of 256 shades of gray and the shades are linearly distributed from 0 (black) to 256 (white). An 8-bit grayscale image does not require a palette but may have one.
An indexed color image is always a palette image. Each pixel is used as an index to the palette. These images can have up to 256 different colors. This includes hues as well as shades. Indexed 8-bit images are good for low color resolution images that do not need processing. They are 3 times smaller than full-color RGB images, but because the pixel values are not linear, many image-processing algorithms cannot work with them. They must be promoted to 24-bit for image processing.
8-bit indexed
This indicates 8-bit indexed color. 8i is used throughout this manual to distinguish between 8-bit grayscale (8-bit gray level) and 8-bit indexed color. An 8-bit indexed color DIB is one where each 8-bit pixel value in the bitmap is used as an index to the palette.The palette dictates which RGB color the pixel displays. These images are compact ways of storing color images. However they are difficult to process because the bytes that make up the pixel can no longer be ordered with any certainty.
Absolute coordinates
Absolute coordinates refer to a common origin, for example, the upper left corner of a display screen. This is the opposite of relative coordinates.ACCUAPI
Accusoft Application Program Interface.Additive primary colors
Red, Green, Blue - the 3 colors used to create all other colors when direct, or transmitted light is used (as in a video monitor). They are called additive primaries, because when these three colors are superimposed they produce white.Aliasing
Aliasing is the appearance of jagged lines caused by digital sampling of curves or diagonal lines. Aliasing is most prevalent in low resolution, low color depth images.Anti-aliasing
Anti-aliasing is a process by which the effects of aliasing are reduced by blending the colors of pixels along sharp borders.Area Of Interest. An area of interest is a rectangle within an image defined as two points within the image. An AOI can be written as (x1,y1)-(x2,y2). All AOIs are parallel with the image's axes.
Application Programmer's Interface. The set of routines that make up a library or toolkit. Some times called a binding.
Artifact
An artifact is a shape that appears in an digitized image that was not in the original, but was created during sampling or image processing steps. The jagged edges produced by aliasing are a type of artifact caused by sampling, while the specks near edges in JPEG images are an artifact caused by the DCT compression algorithm.Aspect Ratio
There are two kinds of aspect ratio that you need to be aware of when working with 2D images; the image aspect ratio and the pixel aspect ratio.
- The image aspect ratio is the ratio of the width of the image to the height of the image.
- The pixel aspect ratio is the shape of the pixels in the image. ScanFix® Xpress requires a pixel aspect ratio of 1:1, to prevent distortions from occurring during morphological operations. A 1:1 aspect ratio means having horizontal and vertical resolutions the same; if they are not, the image should be scaled before any morphological operations are performed.
A curve created from endpoints and two or more control points that serve as positions for the shape of the curve. Originated by P. Bezier (~1962) for the use in car body descriptions.
A raster operation that moves a block of bits representing a portion of an image or scene from one location in the frame buffer to another. Usually written as "bit blt".
A hypothetical 2-D plane containing a single bit of memory for each pixel in a image. If each 8-bit pixel is thought of as a stack of 8 coins, and an image as many rows and columns of these stacked coins then the 3rd bit plane would be the plane consisting of the 3rd coin from each stack.
An image is a bitmap if it contains a value for each of its pixels. This is the opposite of vector images where a small set of values generate an object.
A bitonal image is an image that consists of only two colors, black and white. Bitonal images are commonly dealt with in document imaging processing, because:
- They provided the minimum amount of data needed to represent text.
- They compress efficiently and losslessly.
- They are readily broken down into groups of connected pixels which can be manipulated.
BMP
The Microsoft Windows Bitmapped file format is based on the Microsoft Windows internal bitmap data structures. The BMP format is very widely used and it is quick and easy to read. Although most BMP files are uncompressed, a type of run length encoding is supported.The smallest rectangle that fits around a given object. In imaging, the rectangle is usually rotationally restricted to be parallel to both image axes.
Box Filter
Box filters are used for smoothing, and provide fast, aggressive smoothing to the image. A box filter, or average filter, is a convolution filter with a matrix of all 1's, which has the result of outputting the average pixel value for the window. However, large box filters also tend to produce visibly boxy results due to the use of a rectangular window.BPP
Bits per pixel. The color depths supported by ScanFix® Xpress are: 1 bpp for bitonal images, 8 bpp for gray, and 24 bpp for color.Brightness
The intensity of a pixel, usually expressed in the range of 0 (black) to 255 (white or fully bright color). Brightness of a color image may be defined in a number of ways, depending on the colorspace used.
Commission Internationale de l'Eclairage. (International Commission of Illumination). A standards organization which provides specifications for the description of device independent color.
A function that is passed to another function as a parameter. The function receiving the call-back function can call this function. This is used to change the behavior of a given routine without knowing beforehand what it is expected to do.
A 2-dimensional equally spaced grid iron that uniquely assigns every point in the plane, (one and only one), co-ordinate pair; (x, y). In imaging, each point is usually referred to as a pixel and the x and y values take on integer values. Most images use the top-left as the (0,0), or origin.
CCITT
CCITT is the most widely used compression scheme for transmitting binary (black and white) image data. CCITT was established by the International Telegraph and Telephone Consultative Committee. The Group 3 and Group 4 CCITT compression standards are widely used for transmitting fax data. CCITT compressed images are typically stored in the TIFF image format.An image blending function that replaces pixels of a specified hue range with pixels from a second image. This is often referred to the weatherman effect because most weather forecasters use a solid blue or green background to make it look as if they are standing in front of a huge weather map. It is important to remember that it is the hue that is used in the blending function and not the intensity or saturation.
The clipboard is a windows data structure used to exchanged data between applications. It is a common area where applications place data and others can access it. These operations are usually referred to as Cut (place data in) and Paste (take data out).
Cyan, Magenta, Yellow, (K) black. Computer monitors are additive, but color printers are subtractive. Instead of combining light from monitor phosphors, printers coat paper with colored pigment that removes specific colors from the illumination light.
CMY is the subtractive color model that corresponds to the additive RGB model. Cyan, magenta, and yellow are the color complements of red, green, and blue. Due to the difficulties of manufacturing pigments that produce black when mixed together, a separate black ink is often used and is referred to as K (`B' is already used for blue).
Color Depth
The color depth of an image, expressed in bits per pixel (BPP), is the amount of space needed to store the information to describe the color of a single pixel. ScanFix® Xpress supports bit depths of 1, 8 and 24 BPP.Color Space
A colorspace is a means of representing a set of colors, typically by mapping a subset of the realm of visible colors onto a three dimensional space so that each possible color can be represented by a set of three values. There are many different colorspaces which serve different purposes. ScanFix® Xpress uses the RGB (Red, Green, Blue) and HSV (Hue, Saturation, Value) colorspaces.Comb
A comb is a set of boxes, with closed or open tops, that are used on forms, where each box is typically intended to be filled with a single character. The "teeth", or short vertical lines in the combs, are removed during the comb removal function, leaving only the contents of the boxes.An image processing method for saving valuable disk and memory space by reducing the amount of space required to save a digital image. The graphics data is rewritten allowing it to be represented by a smaller set of data. Do not confuse this with encoding.
The ratio of a file's uncompressed size over its compressed size.
A 2-dimensional blob, for example, a region of interest (ROI), where at least one tangent is drawn that touches the blob at two different locations, and there is a point on the tangent between the two contacts that does not touch the blob.
In simpler words, if a rubber band could be snugly wrapped around a concave blob there would be places where the rubber band lifts off and does not touch the blob. Concave is the opposite of convex.
Container
The container for the component. An object implementing the IContainer interface that represents the component's container, or a null reference (Nothing in Visual Basic) if the component does not have a site.Continuous Tone
A continuous tone image is one where all the colors in the gamut are evenly distributed, allowing blending of pixel values. Bitonal and paletted images are not considered continuous tone, but 8-bit grayscale and 24-bit color images are.Contrast
Contrast is the difference between the darkest and the lightest valued pixels in a given region of an image. Contrast does not apply to bitonal images, which have only pure black and pure white pixels. Contrast is very important in color and gray images, because low contrast data can be difficult to read and process.A 2-dimensional blob, for example, a region of interest (ROI), where every tangent that can be drawn touches the blob at a continuous stretch of the blob's surface with no gaps.
In simpler words, if a rubber band could be snugly wrapped around a convex blob there would be no places where the rubber band lifts off and is not touching the blob. Convex is the opposite of concave.
An image processing operation that is used to spatially filter an image. A convolution is defined by a kernel that is a small matrix of fixed numbers. The size of the kernel, the numbers within it, and a single normalizer value define the operation that is applied to the image. The kernel is applied to the image by placing the kernel over the image to be convolved and sliding it around to center it over every pixel in the original image.
At each placement the numbers (pixel values) from the original image are multiplied by the kernel number that is currently aligned above it. The sum of all these products is tabulated and divided by the kernel's normalizer. This result is placed into the new image at the position of the kernel's center. The kernel is translated to the next pixel position and the process repeats until all image pixels have been processed.
As an example, a 3x3 kernel holding all `1's with a normalizer of 9 performs a neighborhood averaging operation. Each pixel in the new image is the average of its 9 neighbors from the original.
Convolution Filter
A convolution filter alters each pixel's color based on its current color and the colors of neighboring pixels within the filter window, using a matrix of values to determine the weight given to each pixel in the area. When a pixel is processed, its color value is multiplied by the coefficient in the center of the matrix, and any pixels within the window are multiplied by the corresponding coefficients in the matrix. The sum of the products, divided by the Divisor, provides the output value for the center pixel. The convolution filter is typically used for sharpening, softening, and edge enhancement.A pair of numbers that represent a specific location in a two-dimensional plane, for example, an image or on a map.
An image processing method for removing the region near the edge of the image, but keeping the central area.
DCT
A DCT, or discrete cosine transform, is a method of turning sampled data into a collection of cosine waves of varying frequencies. The DCT is most commonly used in the JPEG compression format, where it is used to convert blocks of pixels into waves, and then remove low amplitude elements that do not contribute significantly to the image. The remaining frequencies are stored, and by reversing the DCT, convert the waves back into pixel values can be used to reconstruct a visually similar image. The DCT is typically used as a lossy compression format, which yields very high compression ratios with little loss in quality of the restored image.DCX
An image format containing multiple PCX images. A DCX file can contain a maximum of 1024 images.DDB
Microsoft Device Dependent Bitmap. The actual in-memory information used to display an image.When an image or other digital data set is compressed and stored, it is not usable until it is decompressed into it original form.
DEP
Data Execution Prevention (computer security).Despeckle
A process intended to remove specks from an image. See Speck.The co-ordinates of the coordinate system that describe the physical units that defines the computer screen.
Software written to work on a specific set of hardware platforms. Since these routines make use of physical device attributes, they may behave differently on other devices, although they will most often not work on other devices.
A set of low-level software routines that work with and control a specific hardware device. The names and functions are often standardized across many similar devices. This allows higher level software to use the hardware as a generic device. This frees the higher-level software from dealing with the particulars of specific devices and allows devices to be interchanged.
Software or data structures that are designed to work with or on a wide set of hardware platforms.
DIB
Microsoft Device Independent Bitmap. An alternative file extension used by the Microsoft Windows Bitmap.DICOM
Digital Imaging and Communication, a standard for handling digital medical images.Difference of Gaussian
See Unsharp Mask Filter.Dilate
Dilate is an operation that "grows" objects in an image. In ScanFix® Xpress, the bitonal image processing definition is used, which means that the dilate operation makes black objects get larger, and white objects get smaller.Dispose
Releases the resources used by the Component.Dithering
A technique used in computer graphics to create the illusion of varying shades of gray on a monochrome display or printer, or additional colors on a color display or printer. See also Dot Shading and Halftoning.Dynamic Linked Library. A compiled and linked collection of computer functions that are not directly bound to an executable. These libraries are linked at run-time by Windows. Since Windows is in charge of managing (loading, linking, and removing) the DLLs, they are available to all executables currently running. Each executable links to a shared DLL saving memory by avoiding redundant functions from co-existing. DLLs allow a new level of modularity by providing a means to modify and update executables without re-linking. Just copy a new version of the DLL to the correct disk directory.
Dot Shading
Dot shading refers to the use of halftoning or dithering to create an area of lighter color in a printed document. Dot shaded regions are commonly found in printed forms, and provide special difficulties in removal. ScanFix® Xpress offers a function designed specifically to remove the dots from dot shaded regions in bitonal images. For continuous tone images, a Gaussian filter will often convert dot shading into a solid color.Dots Per Inch. The number of printer dots that can be printed in one inch. The printer's resolution is defined by the number of dots per inch: lower resolution = less dots per inch, higher resolution = more dots per inch.
In an image, an edge is a region of contrast or color change. Edges are useful in machine vision since optical edges often mark the boundary of physical objects.
A method that isolates and locates an optical edge in a digital image.
An edge map is the output of an image-processing filter that transforms an image into an image where intensity represents a change in the contrast (optical edge) of the original image.
Eight-way Connected
Eight-way connected refers to a method of grouping bitonal pixels into an object. An eight-way connected object is one in which pixels that meet on the diagonals are considered connected. See also, Four-way Connected.The format for storing uncompressed data (binary, ASCII, etc.), how it is packed (e.g. 4-bit pixels may be packed at a rate of two pixels per byte), and the unique set of symbols used to represent the range of data items.
An image-processing algorithm that redistributes the frequency of image pixel values allowing equal representation for any given continuous range of values. In an ideal world, an equalized image has the same number of pixels in the range from 10-20 as it does from 200-210. However, since digital images have quantized intensity values, the range totals are rarely identical but usually close.
Erode
Erode is an operation that "shrinks" objects in an image. In ScanFix® Xpress, the bitonal image processing definition is used, which means that the erode operation makes black objects get smaller, and white objects get larger.EXIF
Exchangeable Image File (Japan Electronic Industry Development Association, JEIDA), compressed image format used in digital cameras.
A specification for holding computer data in a disk file. The format dictates what information is present in the file and how it is organized.
An image-processing filter is a transform that removes a specified quantity from an image. For instance a spatial filter removes high, medium or low spatial frequencies from an image.
Float
Denotes a simple type that stores 32-bit floating-point values.Four-way Connected
Four-way Connected refers to a method of grouping bitonal pixels into an object. A Four-way Connected object is one in which pixels that meet on the top, bottom, or sides are considered connected, but diagonals are not. See also, Eight-way Connected.A single picture, usually taken from a collection of images for example, a movie or video stream.
A computer peripheral that stores and sometimes manipulating digital images.
Image-processing algorithms that operate on a single image.
Frequency
Frequency in imaging terms refers to the rate of change in value of a line of pixels. High frequency data consists of rapidly changing brightness or colors, while low frequency data consists of gradually changing brightness or color.
Gain and level are image-processing terms that correspond to the brightness and contrast control on a television. The gain is the "contrast", and the level is the "brightness." By changing the level, the entire range of pixel values are linearly shifted brighter or darker. Gain on the other hand linearly stretches or shrinks the intensity range, altering the contrast.
A non-linear function that is used to correct the inherent non-linearities of cameras and monitors. The intensity of the luminescent phosphor on the raster display is non-linear. Gamma correction is an adjustment to the pixel intensity values that make up for this inherent non-linearity.
Gamut
All possible colors representable by a given colorspace and/or bit depth.Gaussian Filter
A Gaussian filter is a type of convolution filter that uses matrix values generated using a Gaussian curve. Gaussian filters are used to smooth an image, and provide high quality results. However, Gaussian filters tend to be slower than other filters, such as the box filter, because a larger filter window needs to be used to provide the same degree of smoothing as, for example, the box filter.GDI
Acronym for Graphical Device Interface. In Windows, a graphics display system used by applications to display or print bitmapped text (TrueType fonts), images, and other graphical elements. The GDI is responsible for drawing dialog boxes, buttons, and other elements in a consistent style on screen by calling the appropriate screen drivers and passing them the information on the item to be drawn. The GDI also works with GDI printers, which have limited ability to prepare a page for printing. Instead, the GDI handles that task by calling the appropriate printer drivers and moving the image or document directly to the printer, rather than reformatting the image or document in PostScript or another printer language.A class of image processing transforms that alter the location of pixels. This class includes rotates and warps.
GIF
Graphical Interchange File, originally developed by CompuServe as a machine independent format. GIF is one of the most popular image formats for storing 8-bit digitized images. GIF files are typically smaller than uncompressed formats like BMP due to the LZW compression algorithm that GIF uses.A collection of software routines that work on digital images. These collections usually contain routines for drawing various graphical objects, for example, lines, circles, and rectangles.
A shade of gray assigned to a pixel. The shades are usually positive integer values taken from the grayscale. In an 8-bit image a gray level can have a value from 0 to 255.
A range of gray levels. Zero is usually black and higher numbers indicate brighter pixels.
Grayscale or Greyscale
A format of an image that contains only brightness information, but differs from bitonal in that it contains more than 2 colors. Grayscale images supported by ScanFix® Xpress use 8 bits of brightness information, for a range of 0 (black) to 255 (white).A CCITT standard for transmission of facsimile data. It compresses black and white images using a combination of differential, run length and Huffman coding.
Graphical User Interface. A computer-user interface that uses graphical objects and a mouse for user interaction, for example Microsoft Windows.
Halftone
Pertaining to pictures in which gradation of tone in the photograph is reproduced by a graduated system of dotted and checkered spots, usually nearly invisible to the unaided eye, produced by the interposition between the camera and the object of a screen. The name alludes to the fact that this process was the first that was practically successful in reproducing the half tones of the photograph. Halftoning is often used for dot shaded regions in document images, and can be difficult to remove with despeckle algorithms because the halftone dots are often connected. ScanFix® Xpress provides a special dot shading removal algorithm to handle these cases. See also Dithering, Dot Shading.A handle references a data object. A handle is a type of pointer but it usually contains, internally, more information about the referenced object.
High Pass Filter
A high pass filter is a filter that preserves high frequency information, while removing low frequency information. In imaging, high pass filters are used for edge detection and sharpening. See also Low Pass Filter, Frequency.A tabulation of pixel value populations displayed as a bar chart where the x-axis represents all the possible pixel values and the y-axis is the total image count of each given pixel value. A histogram counts how many pixels in the image have a given intensity value or range of values.
Each histogram intensity value or range of values is called a bin. Each bin contains a positive number that represents the number of pixels in the image that fall within the bin's range. A typical 8-bit grayscale histogram contains 256 bins. Each bin has a range of a single intensity value. Bin 0 contains the number of pixels in the image that have a grayscale value of 0 or black; bin 255 contains the number of white (255) pixels. When the collection of bins are sorted (0-255) and charted, the graph displays the intensity distributions of all the images pixels.
Hue Saturation, and Lightness. A method that describes any color as a triplet of real values. The hue represents the color or wavelength of the color. It is sometimes called tone and is commonly known as color. The hue is taken from the standard color wheel and is calibrated in degrees.
Saturation is the depth of the color. It states how gray the color is. It is a real valued parameter from 0.0 to 1.0 with 0.0 indicating full gray and 1.0 representing pure hue.
Lightness determines how black or white a color is. It ranges from 0.0 to 1.0 but with 0.0 representing black and 1.0 white. A lightness of 0.5 is a pure hue.
HSV
HSV is a colorspace consisting of three components called Hue, Saturation, and Value (or Volume). This colorspace is often used by artists, because it provides an easier and more intuitive means of describing color than most other colorspaces. The HSV colorspace is also used by a number of features in ScanFix® Xpress, where the separation of hue, saturation, and value are useful. See also Hue, Saturation, and Value.Hue
One of the 3 components of the HSV color space. The hue represents where on the color wheel a color falls. While Hue is often represented with values from 0 to 359, indicating degrees of a circle, ScanFix® Xpress uses values between 0 and 255, so that the representation will fit in one byte of data.A method of encoding symbols that varies the length of the code in proportion to its information content. Groups of pixels that appear frequently in a image are coded with fewer bits than those of lower occurrence.
There are many digital image formats. Some of these are: TIFF, DIB, GIF, and JPEG. The image format specification dictates which image information is present and how it is organized in memory. Many formats support various sub-formats or `flavors'.
The general term "image processing" refers to a computer discipline wherein digital images are the main data object. This type of processing can be broken down into several sub-categories: compression, image enhancement, image filtering, image distortion, image display and coloring, and image editing.
An image where each pixel value is used as an index to a palette for interpretation before the pixel is displayed. These images contain a palette that is initialized specifically for a given image. The pixel values are usually 8-bit and the palette 24-bit (8-red, 8-green, and 8-blue).
Inverse
To reverse something or change it to its opposite. For example, to invert the colors on a monochrome display means to change light to dark and dark to light. In a digital electrical signal, to replace a high level by a low level and vice versa. This type of operation is the electronic equivalent of a Boolean NOT operation.An image processing operation where each pixel is subtracted from the maximum pixel value allowed. This produces a photographic negative of the original. For an 8-bit image the inverse function is:
invert(pix) = 255-pix;
For an 8-bit RGB image the function is:
invert(Rpix) = 255-Rpix;
invert(Gpix) = 255-Gpix;
invert(Bpix) = 255-Bpix;
JIF
An alternative image file extension used for a JFIF compliant JPEG file. Because many early versions of JPEG contained a JPG extension but did not adhere to the JFIF specifications, the JIF extension was created to identify JPEG files that are JFIF compliant. As the popularity of JPEG grew, JFIF compliance became synonymous with the JPG extension and thus the JIF extension is rarely used.JPEG
The JPEG (Joint Photographic Experts Group) standard is one of the most important image data compression standards. It is widely used in many industries including graphic arts, desktop publishing, medical imaging, and many more. It is also becoming one of the most widely used image formats on the Internet. Although JPEG supports a lossless mode, it most commonly uses lossy compression, wherein a DCT is used to eliminate less important frequencies from the image. The lossy compression allows JPEG to achieve very high compression ratios with little visual impact, though at the pixel level it can result in a significant number of artifacts in the image.Joint Photographic Experts Group. A collaborative specification of the CCITT and the ISO for image compression. The standard JPEG compression algorithm, which is used by ImageGear, is a lossy compression scheme - it loses data.
A small matrix of pixels, usually no bigger that 9x9, that is used as an operator during image convolution. The kernel is set prior to the convolution in a fashion that emphasizes a particular feature of the image. Kernels are often used as spatial filters, each one tuned to a specific spatial frequency that the convolution is intended to highlight.
Laplacian Filter
The Laplacian filter is a convolution filter that works as a high pass edge detection filter, detecting edges in all directions. See also High Pass Filter, Sobel Filter, Prewitt Filter.A dictionary-based image compression method with lossless performance that results in fair compression ratios. Most files are compressed at 2:1.
A collection of software functions that can be called upon by a higher level program. Most libraries are collections of similar routines, for example, those used for graphical or image processing.
A look-up-table or LUT is a continuous block of computer memory that computes the values of a function for one variable. The LUT is set up for the function's variable to be used as an address or offset into the memory block. The value that resides at this memory location becomes the function's output. Because the LUT values need only be initialized once, LUTs are very useful for image processing due to their inherent high speed.
LUT[pixel_value] = f(pixel_value)
LUTs come in various widths, usually in units of bits. An nxm bit LUT has 2n addresses or 256 stored values. Each value is 2m bits wide.
If the second dimension is left off it can be assumed to be equal to the first. In grayscale image processing, LUTs are commonly 8x8, and the bit widths are usually assumed.
A linear LUT, sometimes called a NOP LUT or pass through, is a LUT that is initialized to output the same values as the input. NOP_LUT[pixel_value] = pixel_value.
A method of image compression where there is no loss in quality when the image is uncompressed. The uncompressed image is mathematically identical to its original. Lossless compression is usually lower in compression ratio than lossy compression.
Lossless Compression
Lossless compression is a compression method that preserves all the data in the original, so that the reconstructed image will be exactly the same as the original image. Lossless compression is very poorly suited to dealing the noise typically found in sampled continuous tone images, so it is usually reserved for simpler data such as bitonal images. Most bitonal TIFF compression formats are lossless formats.A method of image compression where some image quality is sacrificed in exchange for higher compression ratios. The amount of quality degradation depends on the compression algorithm used and by a user-selected quality variable.
Lossy Compression
Lossy compression is a compression method that discards relatively unimportant data during compression, so that the reconstructed image will be very similar, but not exactly the same as the original image. Lossy compression algorithms are very common when dealing with audio, video, and image data, as they provide extremely high compression with minimal loss in perceptible quality. Formats that can or do use lossy compression include the JPEG image format, MPEG video, and MP3 audio.Low Pass Filter
A low pass filter is a filter that preserves low frequency information, while removing high frequency information. In imaging, low pass filters are used for smoothing. See also, High Pass Filter, Frequency.Look-Up-Table.
A LUT transform is an image processing method that takes an image and passes each pixel, one at a time, through a pre-set LUT. Each new pixel is a function of one and only one pixel from the original image and is arranged in the same location.
Any image-processing algorithm that transforms a single pixel into another single pixel, both from the same location, can be performed quickly using a LUT.
Square_root_LUT[pixel_value] = sqrt(pixel_value)
LZW
A compression algorithm named after Abraham Lempel and Jakob Ziv (creators of Lempel Ziv compression) and LZW designer Terry Welch that makes use of repeating strings of data in its compression of character streams into code streams. It is also the basis of GIF compression.
A sub-discipline of artificial intelligence that uses video cameras or scanners to obtain information about a given environment. Machine vision processes extract information from digital images about objects in the image. This is the opposite of computer graphics that takes various data describing objects in and produces an output image. Machine vision takes an image in and outputs some level of description about the objects in it, (i.e. color, size, brightness).
Median Filter
A median filter is a filter that uses the statistical median value of a window of pixels to generate the output pixel. Median filters operate in a manner similar to high pass filters, but they have the advantage of preserving sharp edges, while eliminating high contrast specks far more effectively than a comparably sized box or Gaussian filter.Module Size
A module is the smallest unit in a barcode symbology. In 1D and PDF417 barcodes, it is the width of the smallest bar in the barcode pattern. In DataMatrix and QRcode barcodes, it is a square area defining one bit of a code word.An imaging process where one image is gradually transformed into a second image, where both images previously existed. The result is a sequence of in-between images when played sequentially, as in a film loop show, give the appearance of the starting image being transformed to the second image.
Morphing is made up of a collection of image processing algorithms. The two major groups are: warps and blends. Do not confuse this with morphology.
Morphology
Morphology means shape or form. In imaging, morphology refers to the shape of groups of pixels, and algorithms that can alter these shapes. An example of a morphological operation is dilate, which makes black objects get larger, or deskew, which rotates the image contents.Motion Pictures Experts Group. An ISO specification for the compression of digital-broadcast quality full-motion video and sound.
Negate
Negate reverses the brightness of each pixel in an image, creating a photo negative of the original image.A class of image-processing routines that works on neighborhoods of pixels. Each pixel in the new image is computed as a function of the neighborhood of the pixel from the original pixel. The neighborhood ID is defined by a kernel that is set once for each image to be processed.
Noise
Noise is any data in an image that is considered irrelevant and obscures the desirable data in the image. Noise can take many forms, but the most common forms encountered in imaging are the result of either sampling issues or artifacts of processing performed on the image. Sampling issues are caused by dust or other foreign matter on the scanned document or scanner bed, or defects inherent in the document, such as highly textured paper or shaded regions that interfere with text recognition. Artifacts may be cause when thresholding, either on the scanner or by later processing software, produces dots out of shaded regions or sampled noise, or when lossy compression methods such as that used by JPEG results in specks surrounding sharp edges in the image.
Object
An object is any group of connected pixels in a bitonal image; objects in ScanFix® Xpress are generated using Four-way Connection. Objects are important in many ScanFix Xpress functions, such as despeck, blob removal, line removal, and color and blank detection.An image or sub-image that can be placed over a given image. The pixels from the original image are not altered but the overlay can be viewed as if they had been. Usually used to place temporary text and annotation marks, for example, arrows on a image.
Overscan
Overscan refers to the region outside the page but within the scanned region of a document image. Overscan may be black or white.
A binary image is usually stored in computer memory (8 pixels per byte). In this case each byte is referred to as being filled with packed bits. This saves space but makes reading and writing any individual pixel harder since most computers cannot directly access memory in chunks smaller than a byte.
Palette
A palette is an indexed list of colors used to generate an image. Palettes are typically found in non-continuous tone color images, though some image formats, such as the BMP format, do not discriminate between 8 bit continuous tone gray images and 8 bit palette color images. ScanFix® Xpress only handles a limited set of paletted images; those which contain only black and white, and those which contain only 256 shades of gray.A sub-discipline of machine vision where images are searched for specific patterns. Optical character recognition or "OCR" is one type of pattern recognition, where images are searched for the letters of the alphabet.
PBM
Portable bitmap image format, a very simple uncompressed 1-bit (black and white) image format. Data can be stored in either binary or ASCII format.PCX
The PCX image format was originally developed by ZSoft for PC Paintbrush. A version of PC Paintbrush called Microsoft Paintbrush is bundled with Microsoft Windows which established the importance of PCX support. The PCX format uses an RLE encoding scheme which attempts to reduce the size of the image, however, detailed images may result in negative compression which means the file size may be actually be larger after compression.PGM
Portable Gray Map image format. PGM is a very simple uncompressed 8-bit grayscale image format. Data can be stored in either binary or ASCII format.Pixel
A pixel, short for "picture element", is a single sampled value from a digital image. Document images are typically sampled at a resolution of between 100 and 300 pixels per inch (PPI).PNG
Portable Network Graphics (pronounced "ping") provides a portable, legally unencumbered (royalty-free), well-compressed, well-specified standard for lossless bitmapped image files. The initial motivation for developing PNG was to provide a royalty-free alternative to GIF. The design retains many of the features of GIF that make it an attractive format for transmission of images, such as lossless compression and progressive display capabilities. Additionally, it provides several advantages including 24-bit image support and generally better compression, although decompression is typically somewhat slower than GIF. PNG's success will be ultimately determined by its acceptability on the Internet. At the time of this writing, however, PNG has not been incorporated as part of the major Internet browsers.A class of image processing transforms where every pixel is taken, one at a time from an image, and mathematically transformed into a new value with no input from any other pixel in the image. A point process is a degenerative neighborhood process where the kernel is a matrix of pixels that is 1x1 or in other words a single pixel.
An alternative to the usual Cartesian method of addressing image pixels. Polar coordinates use the coordinate pair, angle and radius from an origin instead of column and row.
A special effect that decreases the number of colors or grayscales in an image. The default image pixel contains 256 levels of gray or 256 levels of red, green, and blue. Using this effect reduces these numbers.
PPM
Portable Pixmap image format, a very simple uncompressed 24-bit image format. Data is stored in RGB triplets and can be stored in either binary or ASCII format.Prewitt Filter
The Prewitt filter is a convolution filter used for detecting horizontal or vertical edges. Pixels corresponding to an appropriate edge will show as bright values in the output image, while non-edge pixels will show as dark. The Prewitt filter provides a strong response to horizontal or vertical lines, but less response to diagonals. See also, Sobel Filter, Laplacian Filter.A method of assigning color to ranges of a grayscale image's pixel values. Most often used to highlight subtle contrast gradients or for visually quantifying pixel values. The applied color usually has no correspondence to the original scene. The colors are used only as a guide or highlight.
Quiet Zone
An area of uniform background surrounding a bar code. If the barcode ink color is black and the background white, then a white region around the barcode is the quiet zone. Quiet zones are required for accurate recognition.
A term that describes a single row of a digital image. A raster image is made up of rows of pixels. This is opposed to vector images, where an image is made up of a list of polygon nodes. A raster is sometimes called a scan-line.
Relative coordinates refer to position, as identified as the distance from a local origin.
The process of displaying an image. The final and actual displayed image is said to be rendered.
Resolution
The resolution of a digital image is the rate at which the original was sample, and in document images is expressed in terms of the number of pixels per unit of measure, typically pixels per inch (PPI). Document images are typically scanned at resolutions between 100 and 300 PPI.RGB
Red, Green Blue. Bitmapped images are most generally stored as RGB data. Each pixel or data point in a true color (24-bit) image contains 3 components, red, green and blue, that describe the color of the pixel. Each of the components can have a value between 0 and 255, 0 being the darkest shade of color and 255 being the lightest shade of color. Since each component can be stored in one byte (8-bits), the 3 components take up 3 bytes or 24-bits per pixel.Red, Green, Blue, Quad. A set of four numbers used to describe a color. The forth number is always set to zero. This creates an efficient color LUT or palette. It is more efficient because most computers find multiplying by 4 easier then by 3, as is the case in an RGB triplet.
RLE
RLE stands for Run Length Encoding. It is a lossless compression algorithm that only offers decent compression ratios in specific types of data, typically bitonal or continuous tone images with large regions of flat color.Region Of Interest. A region of interest or ROI is a specification and date structure that allows for the definition of arbitrarily shaped regions within a given image, often called sub-images. A ROI can be thought of as a place holder which remembers a location within an image. ROIs are of several types, each defined in a manor that makes sense for its type.
ROIs are either a rectangle (also called an AOI), square, circle, or a segment list. A rectangle is defined by any two points in the image. From these two points one and only one rectangle can be drawn. A square is defined by a single point and a single length. A circle is defined by its center and radius. A segment list is an arbitrary list of triplets (x, y, xlen); a single point and a length to the right.
Every point in an image is either inside or outside of a given ROI.
Most image processing functions in this package work only within a given ROI. The ROI can encompass the entire image.
Sampling
Sampling is the process of measuring values at certain intervals to generate a digital reproduction of an item. Images are sampled by breaking the image down into a rectangular grid of pixels, then measuring the color or brightness of each pixel.Saturation
One of the 3 components of the HSV colorspace. Saturation controls the purity of a color. Higher saturations result in richer, deeper colors. Lower saturations add gray, resulting in paler colors. Saturation is expressed as a value from 0 to 255.Screen coordinates are those of the actual graphics display controller. The origin is almost always at the upper left-hand corner of the display.
A contiguous section of a raster line. It is defined in physical coordinates by the triplet of its left most point and length (x, y, length).
Sharpen
Sharpening is the use of a high pass filter to emphasize the high frequency elements of an image. Sharpening and smoothing are opposite operations, and most sharpening filters are created by subtracting a smoothing filter from a no-change filter. See also, Unsharp Mask Filter, High Pass Filter.The term "size" can refer to many things when applied to a digital image. These include:
- Pixel size. This is the number of pixels in the image, either as a width times height, or as a total pixel count in megapixels. This size may be change by cropping or rescaling the image.
- File size. This is the number of bytes of storage required by the image. This size can be greatly reduced by the use of compression and noise removal, or by reducing the color depth.
- Print size. This is the size of the original document if printed at "actual size". This unit is obtained by by multiplying the pixel size by the resolution, and may be changed by altering the pixel size or the resolution.
A skew is image distortion that often occurs when a scanner is sampling an image and the image slides to either side before the scan is complete. This has the effect of transforming squares into rhombuses.
Smooth
Smoothing is the process of de-emphasizing sharp, high contrast edges in the image, typically by using a low pass filter. Smoothing algorithms are often used to remove noise in continuous tone images. See also Sharpen.Sobel Filter
The Sobel filter is a convolution filter used for detecting horizontal or vertical edges. Pixels corresponding to an appropriate edge will show as bright values in the output image, while non-edge pixels will show as dark. The Sobel filter provides a stronger response to diagonals than the similar Prewitt filter. See also, Prewitt Filter, Laplacian Filter.Any image processing transform that is applied mostly for its artistic value. Special effects include, wipes, transitions, barn doors, etc.
Speck
A speck is small group of pixels that appear as high contrast noise. In bitonal images, specks usually appear is one or more black pixels, while in continuous tone images they may appear as any color that contrasts with the background. For bitonal images, specks may be removed by the Despeckle or dot shading removal algorithms, and for continuous tone images, a smoothing or median filter can be used.An image processing method that takes a given image and assures that the intensity distribution fills the entire range of possible values. An 8-bit image that is stretched always has at least one pixel with a value of zero and one of 255. The term comes from the before and after histogram of the given image. A stretch operation linearly stretches a histogram so that is ranges from the minimum pixel value to the maximum pixel value.
TGA
Targa Image File format was developed by TrueVision for its Targa line of products. TGA is one of the earliest image formats and was the first popular format to support 24-bit color. TGA supports uncompressed and RLE compressed formats.Thead-safe
An application using this component can use multiple controls running in the same process where they don't interfere with each other. The thread creating the control owns the control and is the only thread that can interact with it.A small copy of an image. Thumbnails are used to display many images on the screen at once.
TIFF
Tag Image File Format, originally released by Aldus Corporation is a standard file format found in most paint, imaging, and desktop publishing programs. TIFF is extremely powerful, flexible, and extensible. However, because of its many nuances and its wide scope, TIFF can be a difficult format to understand as well as a difficult format to support.An algorithm that takes an image, alters it, and outputs a new image. Sometimes written as `xform'.
Three numbers used together to represent a single quantity or location, for example, RGB or (x, y, z).
UI (User Interface)
The controls or API provided for user interaction with an application or component.Unicode
A character set that can support a wide range of international characters. Unicode requires 16-bits to encode a character, unlike ASCII which requires only 8, but supports only a small subset of characters beyond Latin.Unsharp Mask Filter
The unsharp mask filter, also called the difference of Gaussian or DoG filter, is a type of convolution filter used for sharpening an image. The unsharp mask gets its backwards sounding name from the fact that it takes a Gaussian filtered version of the image and takes the difference between it and the original image to de-emphasize the low frequency components, and thus emphasize the high frequency components of the image.
Value/Volume
The brightness of a pixel in the HSV colorspace.A sequence of still images that are transmitted and displayed in synchronous order that give the appearance of live motion.
A geometric image processing routine that distorts an image by spatially compressing and stretching regions.
WMF
The Microsoft Windows Metafile format is used to store vector and bitmap image data. Because of its popularity and wide use, many Windows and non-Windows applications support WMF.The real valued coordinates that make sense for the object, treating it as if it really exists. The world coordinates of a house on a map would be in miles or longitude and latitude. This is the opposite of screen, device or model coordinates.
A mathematical method for referring to a pixel from a digital image. Since most digital images are maintained as a Cartesian matrix of pixels, each pixel has a unique address that can be described as an x or horizontal displacement from the origin and a y or vertical displacement from the origin.
Shorthand for transform.
(Y) luminance, (I), (Q). YIQ is the color model used for U.S. commercial television. It was designed to be backwards compatible with the old black and white television sets. "Y" or luminance is a weighted average of the red, green, and blue that gives more weight to red and green than to blue. The I and Q contain the color components. Together they are called chromoticity.
Z
A mathematical method that refers to a pixel's intensity from a digital image. An image can be written as: I(x,y)=z