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film scanner
A film scanner is a device made for scanning photographic film directly into a computer without the use of any intermediate printmaking. It provides several benefits over using a flatbed scanner to scan in a print of any size: the photographer has direct control over cropping and aspect ratio from the original, unmolested image on film; and many film scanners have special software or hardware that removes scratches and film grain and improves color reproduction from film.
Film scanners can accept either strips of 35 mm or 120 film, or individual slides. Low-end scanners typically only take 35mm film strips, while medium- and high-end film scanners often have interchangeable film loaders. This allows the one scanning platform to be used for different sizes and packaging. For example, some allow microscope slides to be loaded for scanning, while mechanised slide loaders allow many individual slides to be batch scanned unattended.
==Dust and scratches==
Dust and scratches on the film can be a big problem for scanning. Because of their reduced size (compared to prints) the scanners are capable of resolutions much higher than a regular flatbed scanner; typically at least 2000 samples per inch (spi), up to 4000 spi or more. At these resolutions dust and scratches take on gigantic proportions. Even small specks of dust, invisible to the naked eye, can obscure a cluster of several pixels. For this reason, 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, e.g. in Adobe Photoshop and the GIMP. 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. This and other methods can be quite effective, but have the disadvantage that the filter cannot know what actually is dust or noise. It will also degrade fine detail in the scan.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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