Advanced 2D adaptive thresholding estimates the background gray level in a window area around each pixel. The difference between the actual pixel value and the background is then compared to the adaptive settings to determine if a pixel is thresholded as a black or a white pixel.
The additive primary colors are red, green and blue (RGB). These additive primaries represent the three main components of white light. Used individually or together, these three colors of light can be mixed to create nearly all colors. When these three primary colors are mixed in equal parts they produce white. Additive color is used in scanners and computer displays.
ADL+ error diffusion halftoning
Image processing that supports visibility of graytones in printed output by adding toned shades of gray in regions between black and white. Carried out as a segment of dual 2D-adaptive enhancement processing in copy modes.
ALE – Accuracy lens enhancement
Accuracy lens enhancement (ALE) is an electronic correction of spherical errors in CCD based camera scanning systems.
When looking at pixels across the range of a camera, the pixels tend to be more elliptical at the outside edges of the lens and more round in the middle of the lens. This anomaly is known as a spherical lens error and can introduce inaccuracies in the scanning system that can vary quite substantially between different points along the scan line.
Most manufactures typically state a +-0.1% accuracy of the scanner between the two outermost end-points of the scan line. However, when measuring between two points that do not fall across the entire scan line, it is not unusual to see variations of up to +- 0.5% or even higher. This is naturally unacceptable in demanding environments and markets such as GIS, which need a stable and well-defined maximum error of 0.1% or less.
ALE solves this problem by a process to electronically correct the spherical errors in the scanner and maintain a stable maximum error across any two points of less than 0.05% ± 1 pixel.
ATAC – Automatic thickness adjustment control
A special technology that allows the scanner pressure platen to be raised to accommodate thick originals and then lowered – both actions performed by pressing a key from the operators panel. Sensors in the platen detect when perfect pressure is applied to the the original and automatically stop the downwards motion of the platen so it rests on the original with an optimal grip.
An image format made from a matrix of individual pixels.
A bitmapped image is a computer file representing a line-art image that was scanned with a scanner. Refers to the pattern (map) of bits that are either black or white.
The black level is a setting in scan programs used to change dark graytone colors to true black. For example, when copying a brochure with a mixture of text and pictures, the text will often be digitized to a color that we may see as black but really is a dark graytone. When the printer digests this graytone data, it will print the original’s text with a halftone pattern, meaning scattered dots instead of solid black. By increasing the black level value, the text can be copied in real black and will therefore appear clearer.
Black Point Adjustment
An adjustment that will determine the amount of shadow detail in an image. It is considered proper to set the black point so that the darkest part of an image will only just have zero detail.
A process of photographic printing used mainly for copying architectural and mechanical drawings; produces blue lines on a white/bluish background.
The averaging of pixel elements.
An adjustment on a scanner that allows the user to compensate for a light or dark original.
Adjusting a device so that it performs in accordance with an established standard. Scanner calibration is minimizing color deviation between scanned ANSI IT8 reference color patches and the known color reference values. Generally, calibration is the process of setting a device to known color conditions – stabilizing the device to a known and quantifiable state. Calibration is commonly done with devices that change color frequently, such as monitors (phosphors lose brightness over time), scanners (light changes) and printers (proofers and other digital printing devices can change output when colorant or paper stock is changed).
Computer-aided acquisition and logistics support (CALS) standard is a U.S. Defense Department and industry initiative that addresses the design, manufacture, and support issues of generation, access, management, and use of technical data in digital form.
Charge coupled device (CCD) is the image sensor in the scanner that converts light to voltages. These voltages are converted by the scanner into the image.
CCITT Group 3
Standard runlength compression format used with FAX transmission. It utilizes modified Huffman coding to further compress the runlength numbers. Most scanner file formats are dialects of this format.
CCITT Group 4
Two-dimensional compression format, giving very compact image files. Standardized by CALS (MIL 28002) and ISO-ODA for drawing archival and interchange.
Centre Internationale d’Eclairage (CIE) is an international organization that establishes methods for measuring color. These color standards for colormetric measurements are internationally accepted specifications that define color values mathematically. The first color space model, the CIE xyz, was developed in 1931. CIE defines color as a combination of three axes: x, y,and z. The two color spaces released in 1978 are CIELAB and CIELUV. The goal was to provide an accurate and uniform reference of visual perception.
A device-independent color space specified by CIE (see above), used in modern color management software to facilitate conversion of data from a scanner to a display, or from a display to an output device.
The subtractive printing colors: cyan, magenta, yellow, black.
The visual effect of an image when the amount of each color and the overall amount of color are balanced.
Color bit depth
The simplest pixel has two options: black or white. (A pixel with two choices is known as a 1-bit image, or two raised to the power of one). Adding more bit information increases the number of color options. The number of potential color options for a pixel is called color bit depth. For example a 4-bit pixel would have 16 color options, and an 8-bit pixel would have 256 color options, while a 24-bit pixel would have 16,777,216 color options.
An image is said to have a color cast if its colors are not true. A color cast will usually be described by stating the particular color predominant in the image, e.g., the grass appears to have a red color cast.
Used to improve the color rendition. Correcting for, and eliminating an unwanted color cast.
Color management system
Color management system (CMS) software increases the accuracy of color interchange between scanners, displays and printers based on profiles for each device. The CMS is a layer of software resident on the computer that negotiates color reproduction between the application and color devices. The CMS performs the color transformations necessary to exchange accurate color between diverse devices. The color manager needs access to characterization data for the device. The format and content of such device profiles is standardized by the International Color Consortium (ICC.)
Process of separating colors in an image into primary color components for printing. Converting an RGB color image into CMYK color image. Color separation is a technical function during which critical settings such as GCR, black ink limit and total ink limit are applied to the image.
A color space is a particular language used to describe color. Examples of color spaces are: RGB, CMYK, HSV, CIELAB.
The difference between the lightest and darkest significant areas in a picture. A picture with high contrast has nearly white areas and nearly black areas with sharp changes in brightness between them. The picture seems dominated by stark light and dark tones.
Photographers and printers measure transmission in base-10 logarithmic density units, where transmission of unity corresponds to a density of 0, transmission of 0.1 corresponds to a density of 1, transmission of 0.01 corresponds to a density of 2, and so on.
The light-stopping ability of a film. Density is inversely proportional to the amount of light reflected or transmitted by an image.
Device dependent color space
- RGB: A device dependent color space, e.g., the same scan file will appear different when viewed on different computer displays
- CIELAB: A device independent color space is one in which color values are absolute, e.g., defined by CIE standard. CIELAB is the central color space in color management systems (CMS) and is used to translate between different device dependent color spaces such as scanner RGB and display RGB
A file used as part of a color management system (CMS). A device profile contains information about the characteristics of a scanner, computer display or printer. The format for device profiles (Win95, Colorsync, etc.) is standardized by ICC (International Color Consortium).
DIP – Digital image processor
Hardware embedded function that does image enhancement in real-time while scanning.
To use patterns of different colored pixels to create blended colors; or, to use dots of different sizes to simulate grayscale images (see below).
A printing or display device may have only a small number of grayscale or color values for each device pixel. However, if the viewer is sufficiently distant from the printed page or display, the value of neighboring pixels can be set so that the viewer’s eye integrates several pixels to achieve an apparent improvement in the number of levels or colors that can be reproduced.
Dots per inch (dpi)
A measure of dots in a square inch where the individual element is a round dot on the printed page.
DPI (dots per inch)
Equivalent to PPI pixels per inch. An expression of resolution of a scanned image.
Press the left mouse button and move the mouse while keeping the button pressed. When the desired action is completed, release the mouse button. Drag refers to an action sequence (mouse down, mouse move, mouse up), such as “Drag the button in the scroll bar …”
DSP – Digital signal processor
A digital signal processor does image enhancement in real-time while scanning.
Dual 2D-adaptive enhancement
Enhancement processing on the foreground and background separately. Processing is performed on-the-fly. The separate enhancement processes are simultaneously performed on different drawing aspects.
A measurement of scanner quality; the density difference between highlights and shadows.
Modify an entry using standard Windows text-editing techniques.
The light sensitive silver, coated on the clear acetate film base, that forms the photograph when a picture is taken and the film is developed.
Distributing all color or tone equally along a density range.
File format (image)
The format in which a scanned picture is saved. Many programs can insert or import a picture from a file, if it is saved in a file format that the program supports. Common file formats include TIFF (Tagged Image File Format), BMP (Windows bitmap), JPEG (Joint Photograph Expert Group), and FPX (FlashPix format).
To flip the picture left/right.
Foreground when scanning raster data (black and white, or monochrome data) refers to the pixels that represent data of interest (background refers to everything else). Typically, lines and shapes are represented by black pixels (foreground) and empty space is represented by white pixels (background). When scanning grayscale data, background means the gray level of a region of pixels that surrounds some desired foreground data.
An adjustment that makes the tone distribution lighter or darker in an image.
The color range scanable, printable or displayable by a device; e.g., if some of the displayable colors are outside of the gamut of the printer they cannot be printed.
Color management system (CMS) function, where out-of-gamut colors are converted to colors within the gamut of the targeted device, e.g., a printer.
Gray component replacement. A color separation setting used on color photographs where cyan, magenta and yellow inks are replaced by black ink (in a balance that would yield a gray value). The advantages are a reduction in overall ink usage and some increase in image detail.
A term for a black and white photographic image or a scanner setting. Refers to the range of 256 gray tones that make up the image.
The processes of offset printing and laser printing are intrinsically bilevel. However, these devices can reproduce a range of tone levels by halftoning; e.g., an array of widely spaced dots produces the perception of light gray, and an array of tightly spaced dots produces dark gray. Halftone dots are usually placed in a regular grid. In color printing it is conventional to use cyan, magenta, yellow and black grids that have exactly the same dot pitch but different carefully-chosen screen angles.
The lightest part of a picture – reproduced as white on the screen or when printed.
A bar graph representing the statistical distribution of graytones or colors in an image. Each column represents the number of pixels at that gray level or color.
A color space with the three variables of hue, lightness and saturation.
A color space with the three variables of hue, saturation and value.
- Hue means color (as in the color wheel)
- Saturation is an indication relating to the richness or vibrancy of the color
- Value is a term best related to the intensity of light illuminating the object
A named color. In discussions of color that relate to photography, scanning, and printing, six hues are especially important: red, yellow, green, cyan, blue, and magenta. These hues make up every color we can see, and are the designated hues on color wheels.
A measurement of color that can be related by pointing towards a certain color on the color wheel. Hue indicates the relative redness, blueness, greenness, yellowness, etc., of a color.
The International Color Consortium (ICC) was formed to address the need for a common color framework. The ICC has developed a standard device profile that contains information about how various devices render color. This concept is supported by Apple (Colorsync), Microsoft for Windows 95, Sun for Solaris, and by Silicon Graphics for Irix.
A program used to edit pictures to change colors, increase detail, scale or otherwise alter the picture.
Indexed color (or pseudo-color) is the provision of a relatively small number, say 256, of discrete colors in a colormap or palette. For each pixel in the image, the index number of a color is then stored. When retrieving the image, a lookup table uses the index to retrieve red, green and blue components that are then sent to the display. In graphic file formats such as PCX of TIFF, an indexed color image is accompanied by its colormap.
Using the interpolation method of resampling, interpolation generates values for points in between the actual pixels by looking at the surrounding colors or intensities. In a scanner, resolution is increased beyond the actual number of CCD cells. As each line of pixel data arrives from the cameras, new interpolated pixels are added between original pixels. The added pixels enhance line edge definition.
JPEG – Joint photographic expert group
A compressed file format for images. JPEG images feature small file size and speed, but lower quality than other formats.
A method to save storage space by compressing files. JPEG achieves a high degree of compression by discarding non-important picture detail.
File compression and subsequent decompression without any loss of data.
File compression that will compress data to a high degree. When subsequently decompressed, data will have been lost.
Method of lossless compression used with many file formats. Developed by Lempel, Zev and Welch.
The most important part of a picture between black (shadows) and white (highlights).
A reversed photographic image used to produce a positive print or a scanned image.
.NET architecture is a solution for scanning across local networks.
What does it do?
- Enables sharing a scanner on a network
- Enables scanning to a designated scan folder on another computer
.NET architecture allows a a scanner to scan to a client PC in a single coherent and secure process. The client does not need to expose or share his local hard disk as the system can be set up for authorized transfer to the client.
Example of usage – a company that needs to create digital documents of its drawing archive, can send the drawings to a service bureau that scans all the documents directly to the client (company) file server allowing immediate feedback from the client and prevents digital distribution of confidential documents outside the client company.
.NET Architecture also allows users in a company to use a scanner from their own PC workstations although the scanner is physically placed elsewhere. It only need to be on the same LAN. In this way a single scanner is “shared” throughout the company.
A term used to describe the occurrence of pixels that contain random colors within an image.
The paper, negative, slide, or film to be scanned.
The set of colors available for an image.
A graphics file format for pictures introduced on the original Apple Macintosh computer.
The word pixel is a combination of the two words picture and element. It is the smallest building block within a scanned line-art or photographic image. A pixel is the small square picture element that is filled with a color, black or white. The value of a pixel depends on the luminance of the area, and is either a single bit for a black and white image, or multi-bit for a color or graytone image. Pixels come in various sizes and their size is expressed in terms of resolution. Resolution is measured in pixels per inch (ppi) or the equivalent dots per inch (DPI.)
Pixels per inch (ppi)
A measurement of resolution for scanners, where the individual element is a square picture element (see pixel).
A computer language developed by Adobe® Systems, Inc. for printing text, graphics, and scanned images. PostScript is a vector format that can include scanned bitmapped images.
Also called raster image or bitmapped image. A picture composed of individual dots (picture elements, pixels) the way a scanner perceives it. The rows in a high-resolution raster file typically contain 200 or 300 dots per horizontal inch of the original drawing, and there are typically 200 or 300 rows per vertical inch. As each of these dots is defined by location, and by whether it is on or off, raster images generally result in large data files.
A measure of how many pixels per inch (ppi) are scanned.
Resolution defines the level of detail that can be captured or shown by a scanner, display, or output device. Generally, more pixels per inch means more detail in the picture and a larger file when saved.
- Scanners resolution is defined by the number of dots (pixels) per inch (DPI) that can be captured horizontally and vertically, e.g. 300 DPI equals 90,000 pixels per square inch
- Screen resolutions are normally 72 pixels per inch of screen. Additional detail is thrown away by the screen display driver
- Printer resolution scans requires 150 dots per inch and above for good results on the printed output
Resolution of a scanner
Expressed as DPI (dots per inch) or the equivalent ppi (pixels per inch). The higher the resolution of a scanner, the smoother the scanned images.
RGB – Red, green, blue
These additive primary colors are the basic elements of white light. By mixing them on a computer monitor or in a scanned image file, other colors can be created. For instance, red and green produces yellow, and equal amounts of all three produce gray.
RIP – Raster image processor
A RIP is a special software that converts scanned images into a color dithered (halftone) image that can be output directly. An image must be ‘ripped’ before it can be output on a CMYK device, e.g., an inkjet printer.
To turn the picture right (clockwise) or left (counterclockwise) from the orientation in which it was scanned.
A method of compressing raster or bitmap data by representing “runs” of white or black dots along a scanned line as the number of dots in each run. Many variations of this scheme exist, with varying compression efficiency. Typically, runlength compression formats yield a file 20-25% the size of an uncompressed file.
The level of colorfulness of the picture. A picture with high saturation has vivid color. A black and white picture has zero saturation. The purity of a color or the degree to which it is diluted with white light. Red is a highly saturated color. Pink is a diluted red (has lower saturation).
Saturation is one attribute of color in the color space called HSV (hue, saturation, value). Saturation is a characteristic indicating the vibrancy or intensity of a hue. A color with high saturation will appear more intense than the same color with less.
To reduce or enlarge the size of a picture proportionally.
A program that helps adjust the scanner to achieve stable colors and work with a printer. Calibration gives better scanning results and should be run whenever changing printing equipment, toner, and inks, and whenever getting poor results when printing pictures.
A program that helps adjust the computer screen to get the best display of scanned pictures and documents. This program is run during installation and should be used again any time that the computer screen or the lighting around the computer is changed.
SCSI (Small computer system interface)
Specification of interface to computer equipment like disks, printers, scanners etc.
The printed circuit card that came with the scanner. With its driver software, the card allows the computer to talk to the scanner. The card is ASPI compatible with a SCSI-II output connector.
The amount of detail contained in the dark parts of an image. It is desirable to maintain shadow detail, but there is a risk of decreasing overall contrast if lightening the shadow too much in an attempt to expose additional detail. If an image is scanned without shadow detail, it will be impossible to regain detail using an image editing program.
The darkest part of a picture; reproduced as black onscreen or when printed.
An attribute of a scanned image and also an attribute of scanner quality.
Hewlett-Packard and Microsoft proposed the addition of support for a standard color space, sRGB, within the Microsoft operating systems, HP products, the Internet, and all other interested vendors. The aim of this color space is to complement the current color management strategies by enabling a third method of handling color in the operating systems, device drivers and the Internet that utilizes a simple and robust device independent color definition. This is to provide good quality and backward compatibility with minimum transmission and system overhead. Based on a calibrated colorimetric RGB color space well suited to Cathode Ray Tube (CRT) monitors, television, scanners, digital cameras, and printing systems, such a space can be supported with minimum cost to software and hardware vendors.
In large format multiple CCD camera scanners, electronic stitching adjusts for overlap in the field of view of adjacent cameras. Automatic stitching at start of scan ensures that each camera captures the correct number of pixels independently of mechanical and thermal changes.
The subtractive primary colors: cyan, magenta, yellow. As ink applied to a piece of paper by a printer, these colors absorb light and alter the colors seen by looking at the printed paper. Cyan ink absorbs the red third of the spectrum, magenta ink absorbs the green third, and yellow ink absorbs the blue third. This should theoretically cause the viewer to see a black color, but due to unavoidable impurities in the inks, there is still light reflected and the viewer sees a muddy brown. The absence of CMY pigments results in white.
TIFF – Tagged image file format
One of the most common graphic file formats for line-art and photographic images.
Tonal distribution describes the distribution of various bright or dark tones within an image. During the scanning or image editing stage, tones can be redistributed, lightening a dark image or darkening a light one.
A term used in scanning and image editing that refers to compressing the broad range of tones and colors in an image down to the narrower range available on a printer.
The shape of the tone transfer curves can be adjusted by the user to alter color or tone correction. The lower left end of the curve typically represents the dark portions of a picture and an upward bend will typically lighten the shadows. Similar capabilities exist by working with the middle or highlight parts of the curve. In this way it is possible to alter only certain tonal ranges of an image without making unwanted changes to other parts of the image.
Any color or neutral that is denser than white.
True color systems provide eight bits for each of the three components (red, green and blue). Therefore true color is often referred to as 24-bit color.
A standard method of communications that programs can use to send instructions to hardware (such as scanners) and receive data back from them (such as pictures).
UCR – Under color removal
A color separation setting used on color photographs where cyan, magenta and yellow inks are removed from dark, neutral areas and substituted by black ink. The advantages are a reduction in overall ink usage. See also GCR.
Vector drawing (vector file)
Consists of mathematically defined elements, such as “Line from A to B”, “Circle with center and radius”, etc. CAD systems use vector drawings because of their accuracy, relatively low memory requirement and data-file sizes compared to raster images.
Also called raster-to-vector conversion (RTV). The process of automatically converting a raster (bit-mapped) image into a vector (CAD) drawing.
White level is a setting in scan programs used if an original has a background that is not completely white, but ought to be. To get the background to appear as pure white, the white level can be set to a lower value.
White point adjustment
An adjustment that will determine the amount of highlight detail in an image. The white point should be set so that the lightest part of an image will only just have zero detail.
The CIE system is based on the description of color as a brightness (luminance) component Y, and two additional components X and Z. The spectral weighting curves of X and Z have been standardized by CIE, based on statistics from experiments involving human observers. XYZ tri-stimulus values can describe any color.
The ability to enlarge or shrink the view of the picture in a window. Zoom does not alter the size of the final scanned picture; it only provides a better view while creating a selection border on the screen.