Old writing back in 1998 - may not apply now.  


Even if you purchase a digital camera, that is for the future. Digitise and manipulating your current work with past works demand you to know how to handle scanning - convert them to a digital format for use on the computer.
Scanners works by a method of reading a reflective print, negative, or transparency and converting the amount of light transmitted or reflected into a specific value and putting those encoded value into a digital computer file. As an overview article, we won't be going to much detail in topics like the technicality how it works inside a scanner. But you need to know the few different types of scanners. Flatbed grey scale and colour scanner
Slide Scanners,
Drum Scanners

 

The Umax PowerLook II flatbed - one of the best in town It is quite possible that, depending on your application and knowledge in scanning, you could produce some very pleasing and professional results even with some lower entry flatbed scanners. Greyscale scanners are scanners with CCDs (charge coupled device) that can differentiate between levels of light and thus convert pixels into a number of shades of grey. most flatbed scanner can handle 256 levels of grey, however there are many high-end systems that can produce much more levels (4096, 32768, etc.).

The Umax S12 - 33-bit equivalent color through analoggamma corrections. Good entry flatbed model (my office have three of these for general purpose scanning) Color flatbed scanner forms the bulk of the market. Today, 600dpi (dots per inch) 24-bit scanner is quite popular the desktop publishing business. Depends on your available computer "power" (hard disk size, RAM (Random Access Memory) & speed) not all the full blown features advertise in the magazine can be utilised fully. Doing a high resolution scan demands you a lot of RAM (computer memory) and occupies a lot of your hard disk space. It is not uncommon in desktop publishing where computer with 80 MB to 512 MB RAM and 2-4 gigabytes of hard disk capacity so it is not a problem for them. Color scanners are basically grey scale scanners that have additional filtration process (Red, Green, and Blue, group to known as "RGB", where the black color is stimulated) and make multiple passes to generate 256 levels of each RGB component. Most scanners come with its dedicated software which recombines the three passes to create full color. Higher quality scanners perform all three scans in one pass at the same time to preserve registration.

The ScanMaker III is Microtek's flagship scanner. The III is a fast, single-pass 36-bit flatbed, with 600 x 1200 dpi optical resolution, 3.4 dynamic range

Current color scanning technology is facing with a real physical limit as to how many CCD ICs can be placed side by side in one inch . That translates with the highest resolution flat bed scanning system is physically limited to 600 spots (pixels) per linear inch. Some manufacturer advertised their flatbed scanner can offer 1200, 2400, and even 9600 dpi. which is not so true in real life applications, where currently the bottleneck is the real physical limit as to how many CCD ICs can be placed side by side in one inch and that limitation is 600 right now. (Resolution (number of pixels)is controlled in two ways. Horizontal scale : The number of pixels is controlled by how closely the CCDs are placed next to each other along the single row while in vertical scale, the number of pixels is controlled by how slowly the light bar and mirror inch along the length of the flat original (the print, slides etc), and thus reflecting onto the CCDs inside. Basically, it means the more CCDs and the smaller the steps of the advancing light bar, the greater the resolution.). Those advertised data are merely referring to "interpolation". Interpolation is a software process - this is just like those sampling rate in the Audio CD players, whereby the scanner essentially samples two pixels and averages the two pixels together to form an extra pixel (or more) in the middle. Most scanners utilise interpolation to enhance the data by stimulation - created by averaging.


              

Slide scanner


Nikon CoolScan for 35mm Transparencies

For those of you who only works with slides, unless you are dedicated to the 35mm, try to invest into a multi formats slide scanner which allows you to play around with 120, 4x5 or the new popular panorama strips. Nikon has the LS-4500AF which handles multi formats, for 35mm transparency or negative, it scans at 3000 dpi, good enough for exact reproduction of 35mm size. Well, unless for some specific tasks, I don't suggest to scan with the highest possible resolution, because you have to understand some facts, like the limit of what is on the film. Most modern films and lenses can only resolve around a hundred line pairs per mm (look at those MTF chart and you'll know what I meant); that means that only 3500 pixels can be resolved clearly across 35mm film. To try to scan the maximum resolution, say 5000, 6000 or 9600 pixels across a 35 mm film, for instance,can be quite wasteful. Besides, the file size quadruples as resolution doubles, so file sizes can be very huge with high resolution scanning. Further, it is not easy and economical and also can be time consuming to work with the large files on a computer - which you might need additional RAM or faster processor's machine, not to mention the cost of system time and editing time later.

Agfa SelectScanPlus with 6,000-element linear-array CCD a maximum resolution of 8,000 pixels per inch

Before you scan, remember, high resolution scan needs appropriate big print to show all its detail. Too small a print will just waste your initial effort on high resolution scanning. Just make sure to match final print size to file size. So, scan your work with a purpose. If you are not sure what print size you want in advance, you should scan at the appropriate resolution for the size of the original.

Nikon Scantouch Tri-passes with 1200 dpi

A friend of mine in the bureau has given me some guidelines for purposeful scanning which I do hope you can be beneficial to these references:

35mm 4000 x 2666:  prints sharp up to 11x14"
6x7  6144 x 5200:  prints sharp up to 16x20"
4x5  8000 x 6400:  prints sharp up to 20x24"
 

Drum Scanner For those of you, who doesn't think of investing into a digital camera/back or a in house flatbed or a slide scanner, commercial colour separation labs can handle your work for you (make sure you have the removable storage device (harddisk, optical disk, Syquest or Zip drive) to transport it back to your home or office, ha!). Most establishments of such labs now are dedicated to service the advertising agencies and most are equipped with a drum scanner, providing the maximum scanning quality for huge and large prints output. Nevertheless, apart from the high end scanning systems, they do accommodate high quality small jobs. I'll compile some of these labs who offering such services for your inquiries in the future. Anyway, this section is too narrow for public consumption, besides, those people in the service bureau can "kill" me for saying anything wrong (to be honest, I have not much exposure on drum scanning - except what I have pick up from them through business correspondence!)

The Arcus II by Agfa (Next time I will tell you my bitter experience with this model) The next and final part, we will discuss about "on screen" manipulation of the digitised image, direct source from digital camera/ scan back or by means of scanning.

[ Introductory ][ High End Models][ Entry Models][ Scanner ][ On Screen ][ Gamma ][ CCD ] [ Glossary ]


Agfa, Arcus are trademarks of Agfa-Gevaert Group; Umax, PowerLook II, Vista S12 are trademarks of Umax Inc; ScanMaker III, Microtek are trademarks of Microtek International Inc; Nikon CoolScan, ScanTouch are trademarks of Nikon Corporation Inc.

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