Image Scanner - Quality

Quality

Scanners typically read red-green-blue color (RGB) data from the array. This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface (usually USB, previous to which was SCSI or bidirectional parallel port in older units).

Color depth varies depending on the scanning array characteristics, but is usually at least 24 bits. High quality models have 36-48 bits of color depth.

Another qualifying parameter for a scanner is its resolution, measured in pixels per inch (ppi), sometimes more accurately referred to as Samples per inch (spi). Instead of using the scanner's true optical resolution, the only meaningful parameter, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software interpolation. As of 2009, a high-end flatbed scanner can scan up to 5400 ppi and drum scanners have an optical resolution of between 3,000 and 24,000 ppi.

Manufacturers often claim interpolated resolutions as high as 19,200 ppi; but such numbers carry little meaningful value, because the number of possible interpolated pixels is unlimited and doing so does not increase the level of captured detail.

The size of the file created increases with the square of the resolution; doubling the resolution quadruples the file size. A resolution must be chosen that is within the capabilities of the equipment, preserves sufficient detail, and does not produce a file of excessive size. The file size can be reduced for a given resolution by using "lossy" compression methods such as JPEG, at some cost in quality. If the best possible quality is required lossless compression should be used; reduced-quality files of smaller size can be produced from such an image when required (e.g., image designed to be printed on a full page, and a much smaller file to be displayed as part of a fast-loading web page).

Purity can be diminished by scanner noise, optical flare, poor analog to digital conversion, scratches, dust, Newton rings, out of focus sensors, improper scanner operation, and poor software. Drum scanners are said to produce the purest digital representations of the film, followed by high end film scanners that use the larger Kodak Tri-Linear sensors.

The third important parameter for a scanner is its density range or Drange (see Densitometry). A high density range means that the scanner is able to record shadow details and brightness details in one scan. Density of film is measured on a base 10 log scale and varies between 0.0 (transparent) and 4.0, about 13 stops. The maximum density of negative film is up to 3.0d (density), while slide film can reach 4.0d. Slower film can reach higher density than faster film. Consumer level flatbed scanners have a Drange in the 2.5-3.0 range, adequate for negative film. High end flatbed scanners can reach a Drange of 3.7. Drum scanners have a Drange of 3.6-4.5.

By combining full-color imagery with 3D models, modern hand-held scanners are able to completely reproduce objects electronically. The addition of 3D color printers enables accurate miniaturization of these objects, with applications across many industries and professions.

Read more about this topic:  Image Scanner

Famous quotes containing the word quality:

    Anybody who knows the difference between the kind of conversation you have walking in the woods and the kind of conversation you have between the segments of a show on Nickelodeon can tell you that quality time exists. Quality time is when you and your child are together and keenly aware of each other. You are enjoying the same thing at the same time, even if it is just being in a room or going for a drive in the car. You are somehow in tune, even while daring to be silent together.
    Louise Lague (20th century)

    There’s no nation under the sun can beat the English for ill-politeness: for my part, I hate the very sight of them; and so I shall only just visit a person of quality or two of my particular acquaintance, and then I shall go back again to France.
    Frances Burney (1752–1840)

    There are few things more disturbing than to find, in somebody we detest, a moral quality which seems to us demonstrably superior to anything we ourselves possess. It augurs not merely an unfairness on the part of creation, but a lack of artistic judgement.... Sainthood is acceptable only in saints.
    Pamela Hansford Johnson (1912–1981)