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Table of contents
A device converting analog signals (e.g. from a microphone) into digital form for further processing.
Bit is an abbreviation for binary digit. A bit can only contain the value 1 or 0. The bit is a basic data unit in the digital computing and communications domain.
The bit depth refers to the amount of information a scanner is capable of recording per pixel. The higher the bit depth, the more color/gray gradations a scanner can record, therefore resulting in higher image quality.
CCD (Charge Coupled Device), a light sensitive electronic device capable of converting light into electrical charges. A CCD is used as an image sensor for many digital imaging devices including digital cameras and scanners.
Contact Image Sensor, also a type of light sensitive electronic device (like the CCD), CIS-based scanners are often smaller and much more affordable in comparison to CCD-based products and consume less power, but the trade-off is they produce slightly lower-quality scanned images.
CMYK (Cyan, Magenta, Yellow, and Black) is a subtractive color model usually utilized in color printing. The mixture of CMY colors is subtractive; printing cyan, magenta and yellow together on a white paper results in black. But the "black" generated through mixing CMY colors is not ideal most of the time, so additional black is added for better printing quality.
Color correction is an image adjusting process intending to "correct" or compensate the color deficiencies caused by scanners or output devices. It is important to ensure the color accuracy through the whole image processing flow.
Dynamic range, also known as optical density (OD) or density range, is a measure of the scanner’s ability to record different tones of an image. Dynamic range is measured on a logarithmic scale from 0 to 4. 0.0 represents perfect white, while 4.0 represents perfect black. The dynamic range is actually the difference between the darkest and brightest optical density that the scanner can capture. The bigger the difference, the larger the dynamic range, and the better image quality the scanner can offer.
DPI (Dots per Inch) is a measurement of the scanner resolution which is the number of pixels/dots a scanner can sample/capture per square inch in a given image. PPI (Pixels per Inch) is usually equivalent to DPI when referring to scanners.
Common scanners can only scan one side of a the target object during a single pass, while duplex scanners can scan both sides as they often carry two image sensor/scan heads. Duplex scanners, therefore, tend to cost more as well.
Flatbed scanners are the most common desktop scanners that look and work like small photocopiers. The target paper or object to be scanned is placed on a pane of glass; light emitted from under the glass reflects off the objects and is captured by the image sensor in the moving scan head.
Interpolation is a method used to generate new data from existing data. In the digital imaging domain, interpolation is the process used to increase the resolution of the original image by generating new pixels from existing pixels and computing the colors of the new pixels based on neighboring pixels. Interpolation cannot generate detail that is not in the original image.
JPEG (Joint Photographic Expert Group), a lossy compression algorithm, is one of the most commonly-used image compression standards. The file format utilizing this compression scheme is always called JPEG as well.
A negative is a type of film that records colors or monochrome shades in the reverse, which means that the dark areas will appear white on a negative.
In scanner terms noise refers to incorrectly recorded pixel values. These are generally caused by electrical interference or device malfunction.
OCR (Optical Character Recognition) refers to the process of recognizing characters in printed text images (generally captured by scanners) and converting them into computer-editable text. This is usually achieved by OCR software which transfers printed document text into word processor text without involving manual typing.
The pixel is the smallest indivisible unit of a digital image. It is a word created from "picture element". All computer images are made up of pixels. The term pixel is usually interchangeable with dot, but the pixel mostly refers to the screen dot rather than the image dot.
A measurement of scanner speed. PPM (Pages per Minute) refers to the number of pages scanned per minute, while IPM (Images per Minute) refers to how many images that can be scanned per minute. They are equal for common scanners, but IPM doubles for duplex scanners since they can scan both sides of a page simultaneously.
The resolution figure refers to the number of pixels a scanner can sample/capture, typically measured in dots per inch (dpi). Scanners with higher resolutions are capable of recording more detail from a given image, thereby resulting in scanned images with greater detail than those from lower resolution scanners.
RGB (Red, Green and Blue) is an additive color model meaning that the red, green and blue lights are combined for color reproduction. Mixing the same amount of the three primary colors (red, green and blue) makes white. Most computer monitors and image-editing programs utilize the RGB color model.
SCSI (Small Computer System Interface) is an interface standard for transferring data between SCSI peripherals and computers. Most PCs do not support the SCSI port, so a SCSI controller card needs to be installed if you plan on purchasing a SCSI scanner.
Unlike flatbed scanners, sheetfed scanners are more like fax machines/printers than photocopiers, as they work by moving the target document/print instead of the scan head.
A transparency (also known as slide or reversal film) is a positive image created on transparent film.
TWAIN (not an official acronym) is widely known as "Technology/Toolkit Without An/Any Interesting/Important/Intelligent Name". TWAIN is an industry standard for communications between digital imaging devices (such as scanners and digital cameras) and computer application software. TWAIN allows you to import/acquire an image into/from your software.