How do Scanners Work?
This data is then processed with an algorithm to correct for different exposure conditions and sent to the computer, via the device's input/output interface. Color depth varies depending on the scanning array characteristics. The other qualifying rating 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, one of the key parameters, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software interpolation.
Manufacturers often claim interpolated resolutions as high as say 18,000 ppi; but such numbers carry little meaningful value, because the number of possible interpolated pixels is unlimited. The higher the resolution, the larger the file however there comes point where size does not matter so much. Itís a trade off between quality and manageability.
3rd important parameter for a scanner is its density range. A high density
range means that the scanner is able to reproduce shadow details and brightness
details in one scan. Looking into the technical aspects it can be stated
that interpolation is a technique where the resolution of an image is
increased from its original size to a higher or larger resolution. The
spatial resolution of an image is itís horizontal x vertical pixel count.
For example 1600 x 1200. Software interpolation can be performed on a
digital image using a one of a number of image editing programs. This
is often called as resizing and is done with a computer and performed
on an image file. Also, it shoud be noted here that JPG is a compressed
image file format. Whenever a file is saved as a JPG file, image data
is lost forever in the compression process. The quality original data
is thrown away in exchange for file-size efficiency. Software interpolation
is a process performed after the JPG losses have been applied.
Film Scanners Domestic Film scanners can generally accept either strips of 35 mm or 120 film, or individual slides. Low-end scanners typically only take 35mm film strips and medium- and high-end film scanners often have interchangeable film loaders. This facilitates the one scanning platform to be used for different sizes and packaging.