How do Scanners Work?

Overview:
A scanner is a device that optically scans images,or an object and converts it to a digital image. Common examples are variations of the flatbed scanner where the document is placed on a glass window for scanning. Scanners typically read red-green-blue color (RGB) data.

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.

The 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.

A film scanner is a device made for scanning photographic film directly into a computer without the use of any intermediate printmaking. They provide several benefits over using a flatbed scanner to scan in a print of any size ó the photographer has direct control over cropping and aspect ratio from the original unmolested image on film, and many film scanners come with specialized software or hardware designed to remove scratches, film grain, and improve color reproduction from negatives.

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.

Dust & Scratches:
Dust and scratches on the film can be a big issue for scanning. Because of their small size the film scanners are capable of resolutions much higher than a regular flatbed scanner, typically at least 2000 samples per inch (spi), up to say 36000 dpi. At these resolutions dust and scratches take on relatively large proportions. Even small specks of dust, invisible to the naked eye, can obscure a cluster of several pixels.

For this reason, digital techniques have been developed to remove their appearance from a scan, see film restoration. The simplest is the median filter, often called despeckle in many graphic manipulation programs. It works by examining a pixel in relation to the pixels surrounding it; if it is too different from the surrounding pixels then it is replaced with one set to their median value.

Whilst this and other methods can be quite effective, they can have the disadvantage that the filter cannot know what actually is dust or noise. It will also obliterate fine detail in the scan. For this reason, itís often best to remove as much dust before scanning and then effect changes thereafterwards.

Slide Scanning Prices and Options