Film scanner
A slide - scan is a special reproduction method, in which a slide is digitized by means of a slide scanner.
Basic principle
The illuminated slide is scanned line by line. The different colors and brightnesses pixel by pixel converted and stored in digital signals.
Resolution
The resolutions good slide scanner in the amateur are now at 4600 ppi, semi-professional devices reach 7200 ppi. Higher resolutions are often reached only by drum scanner. Since good devices can not only scan with a high dot density, but also with a very high density range, they are able to transfer appropriate to the high contrast range of a slide. Of such scanned slides produce very large image files: With a slide of 24 mm × 36 mm as arising at 3600 ppi already about 17 megapixels, at 6400 ppi about 54 megapixels. Such large image files are not in all applications makes sense because for most applications (projector, small prints, ...) suffice significantly smaller amounts of data.
Slide scanner
Slide scanners are purpose-built scanner to digitize framed slides and in most cases with negative films. The commercial for the amateur and semi-professional appliances are generally built for the small picture format; but there are also scanners for medium format templates available. Some models have the option of using an adapter to handle multiple slides in batch mode. The digital output format ranges from about JPG TIFF to RAW.
Depending on the manufacturer have the slide scanner via a USB or Firewire interface.
Some hardware and software developers have developed special technologies that can take great impact on the quality of the scan result. Relevant are, among others:
Dust and scratch correction
On many slides there are scratches or fingerprints; Dust particles can hardly be avoided completely. A small speck of dust can be projected onto a screen, like a bird act at the blue sky. There are several methods to detect such defects even when scanning and to eliminate:
ICE, SRD, iSRD, Infrared Cleaning
ICE is an abbreviation for Image Correction and Enhancement, SRD stands for Smart Removal of Defects, iSRD sets such as ICE and Infrared Cleaning in addition to the infrared channel of the scanner. The long wavelength infrared light radiated through the color emulsion of negatives and slides almost unhindered; Scratches, dust and lint, however, cast a shadow. From the thus determined position data, infrared technology can be based on the surrounding pixels to perform an automatic dust and scratch correction. In the case of the image iSRD is scanned in two passes. In the first pass of the infrared scanning is performed in the second half of the regular RGB scan. Subsequently, the calculated dust and scratch removal is an additional image channel, which is automatically created from the infrared image. iSRD works with a few exceptions with all inspection scanners that have an infrared light source and can be, as opposed to ICE to operate manually. The picture quality can be further improved by additional options such as different degrees of corrections to certain image parts. ICE is implemented in hardware in many current devices. SRD and Infrared Cleaning, however, are pure software implementations on the PC side that use the raw data of the infrared channel. Therefore, in principle, work with any scanner.
Almost all methods that use the infrared channel, but fail in film based on silver (this applies to the majority of black and white films). Also in Kodachrome Diapositivfilmen the results are useless because of the special structure ( three layers on a silver basis ) usually. The long-wave infrared radiation can not irradiate materials contained in these films, such as silver particles. These particles are therefore treated as defects, ie retouched. The resulting image is very blurred. In 2004, the company with the Nikon Super Coolscan 9000 ED scanner out, which can liberate ( ICE4 Professional) without additional Software from dust and scratches Kodachrome films with the aid of an improved ICE procedure. With iSRD and Infrared Cleaning can now also Kodachrome slides without loss of sharpness reliably remove dust and scratches. Also helpful is a previous calibration with a special Kodachrome IT8 target.
FARE, Car Dust
Some scanner manufacturers market different, proprietary processes for dust and scratch removal under different brand names.
Noise Reduction with Multi-Sampling
Here, the image is scanned several times and assigned to each pixel in the image the average of the pixel values of all individual scans. A four -scan leads in theory for a better by a factor of two signal -to-noise ratio. Some scanners support multiple scans directly, ie, the sensor is able to read the same row multiple times in a row. This is not possible, can be alternatively successively make and process multiple single complete scans. Mechanical tolerances can this result in otherwise that the individual scans are not exactly congruent, which can result in blurred images.
Extension of the dynamic range with Multi-Exposure
This method was developed by LaserSoft Imaging. It only works with scanners, where you can change the exposure intensity. The dynamic range is crucial for the quality of a recording; in general, a larger dynamic extent better results. The use of multiple layers with different sensitivity reach modern black and white films, color negative films and slide films a high dynamic range when recording, which can be detected by normal (single ) scanning only a very few high-quality scanners. With multi-exposure, the maximum dynamic range, so that of the original is retained by multiple scans with different exposures. This method differs from traditional multi-sampling, in which by repeated scanning of the same general exposure intensity noise is reduced in the image; this is achieved by multi-exposure in addition.
Microscopy
Some types of scanners are also suitable as replacement microscope. Instead of a slide holder is used with the imaged specimen and scanned at them. To this end, some manufacturers offer at specially developed accessories, but can be such a holder may also, by using a double-walled glass slide mount improvise.