The Scanning of Colour and B&W Film and Photographs for Image
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Downloaded from The Scanning of Colour and B&W Film and do we need to capture from the original? I will largely ignore photographic prints as any quality 600 dpi reflective flatbed scanner is more than adequate Photographs for Image Processing, Analysis for these. Standard quality 35 mm colour film is about 6,000 dpi. However a and Archiving - On a Tight Budget high quality prime camera lens can only resolve nearer 4,000 dpi, although some extra detail may be seen in the film at 6000 dpi. Cheaper consumer https://www.cambridge.org/core Keith}. Morris zoom lenses or film projectors will do worse than this, often dropping detail Cell Biology Division, The Institute of Ophthalmology, UCL, UK to nearer 1,500 dpi. Scanning to or above the film's resolution always produces [email protected] a soft (looks slightly out of focus) digitised image, as the scan sampling now matches or exceeds the films resolution. Assuming a typical film resolution of Despite the advent of the new PC based digital camera era, there is still 120 line per mm (a fairly reasonable number), and that it takes two scanned a vast archive of film. The obvious thing to do is to scan film optically using pixels to represent the line pair, film resolution works out to an equivalent a high resolution film scanner and to convert the image into a digital file for of about 6,000 dpi. Some films claim considerably higher resolving power digital distribution, PC archiving, and image processing. The likes of NASA - 200 lines per mm (lpm) for Acros, for example. Thus, high-end drum can easily afford the best $20k plus PMT drum scanners and pro flatbed scans of 8,000 dpi make sense within that context. The resolving power of . IP address: scanners for their spaceflight photo archives. See some professional scanners Kodachrome II (where two lines can no longer be separated) is 64 lpm, thus at http://www.imacon.dk, http://www.aztek.com, http://graphics.kodak.com 30 |^m structures are the smallest that be resolved with this film. (Creo) and http://www.flatbed-scanner-review.org. You can download selec- tions from the NASA digitised archive at http://grin.hq.nasa.gov. The line resolution of TEM film is typically better than 200 lpm. In TEM 170.106.35.229 it is desirable to maximise electrons for exposure, with slight over-exposure An optical 8000 dpi Hasselblad Imacon Flextight 848 drum scanner using a very slow film type. In general terms, resolution of a TEM is equal costs around $15k, with the 949 around $25k. With drum scanners there is at all magnifications but a low magnification image may require enlarging. no glass between the detector and the film, unlike that found in professional Beyond 20x photographic magnification, insufficient electrons have formed , on flatbeds such as the Kodak 'Creo' $ 12k [4300 dpi] IQSmart, the $45k [ 8000 to the image and "noise" becomes intolerable (Jim Darley, Probing & Structure 14000 dpi] EverSmart Supreme II flatbeds and far cheaper consumer 'photo' 24 Sep 2021 at 15:29:52 Microscopy Supplies & Accessories). Optimum TEM negative enlargement flat beds such as the new Epson V750 at $750. Top end scanners are used is about 6x, although up to lOx to 12x produces acceptable results with Ko- by imaging professionals for things like magazine production and museum dak 4489, although grain noise from the tissue support resin may become film archiving. Cheaper dedicated 35mm slide and negative scanners also objectionable at high EM magnifications. Optical microscopes have used have no glass between the lens and the film surface, although few, other than film for well over 150 years to capture complex magnified images, and the $800 Epson 3200 [dpi], can scan negatives greater than 9x6 cm, e.g. the have mostly used colour slide film since the 1950s - the main medium for 4000 dpi Nikon 35 mm L50ED at $500 and the $2,500 4000 dpi 35mm to 9 , subject to the Cambridge Core terms of use, available at presentations at the time. In addition, many researchers will have archives x 6 cm Nikon LS9000 ED film scanner. As well as offering better optics and of images of such things as laboratory equipment and presentations on detectors, higher priced scanners have important adjuncts like attachments 35mm film, plus possibly 'Polaroid' or standard photographic prints (with to greatly improve the film throughput, essential if you have an archive of the negatives now lost). 50,000+ colour slides. In B&W film there is usually one layer of silver salts. When the exposed While some of these prices may appear a lot just to scan film, install- grains are developed, the silver salts are converted to metallic silver, which ing a 2k x 2k or higher resolution digital camera on a transmission electron block light and appear as the black part of the film negative. Colour film uses microscope can easily cost around £20k to £45k per TEM system. So many at least three layers. Dyes added to the silver salts make the crystals sensitive stick with traditional Yt plate B&W TEM developed film negatives. Recently, to different colours. Typically, the blue-sensitive layer is on top, followed by prices of high resolution 4,000 dots per inch (dpi) consumer flatbed scanners the green and red layers. During development, the silver salts are converted have tumbled, facilitating a cheap way to digitise film for figures in papers to metallic silver, as with black and white film. The by-products of this or for subsequent image analysis. This has eliminated the need to produce reaction form coloured dyes. The silver is converted back to silver salts in photographic prints from TEM negatives, and allows easy post scan edit- the bleach step of development and is removed from the film in the fix step, ing and photo-stitching of negatives that would have taken hours in the leaving just the co- traditional darkroom. loured dyes. Some The black and white (B&W) silver halide process produces a far more films, like Koda- A https://www.cambridge.org/core/terms stable image compared to those produced with colour dye substitution (co- color II, have as lour slides and negatives). Walt Disney famously created B&W red, green many as 12 emul- and blue filter film masters of cartoon films like Snow White to overcome sion layers, with problems associated with colour dye fading. The support material, particu- upwards of 20 dif- larly old celluloid and nitrocellulose stock, may degrade badly with time ferent chemicals in even as B&W film, although storage conditions are critical. Modern film each layer (http:// uses tough polyester as a base. Early photographers used glass plate as the en.wikipedia.org). support medium that was also very durable - until you drop them. Colour As Bob John- fading is a serious problem with colour film - although some colour film son (http://www. processes are more stable than others. Fortunately, much of the original earthboundlight. colour can often be restored with digital image processing after scanning. com/phototips. https://doi.org/10.1017/S1551929500057667 I suppose we should use 'acid free' bag storage to protect our colour nega- html) points out, tives, photographs, and slides from atmospheric pollution and decay - just comparing the size the same as the valuable linen, comic and book owners do (e.g. http://www. of 'photosites' in savemycomics.com, http://www.conservation-by-design.co.uk ). Modern digital cameras to B&W TEM film like Kodak 4489 has robust polyester as the support medium that of film grain D and an estimated archive life of about 500 years if stored carefully. Colour yields some inter- Figure 1. The three photo flatbed and one drum film and prints often faded rapidly as the dyes used in earlier film production esting results. The were far less stable than modern ones. scanners used to produce the images in the other Nikon D2x digital figures. (A) The $400 Epson 4990 Photo (B) The To prevent our treasured film and photographs being lost to air pollution SLR camera has a $5,000 Agfa Duoscan 2550T (C) The $400 Canon or damage, the obvious answer is to scan the film into a digitised PC image sensor that mea- 9950F (D) The $12,000 Hasselblad Imacon Flextight file (where PC archiving is still an important issue). But how much detail sures 23.7 x 15.7 848 drum scanner 42 miCROf COPY TODAY May 2006 43 Buehler 5/8/06 3:43 PM Page 1 Downloaded from https://www.cambridge.org/core . IP address: 170.106.35.229 , on 24 Sep 2021 at 15:29:52 , subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms Results are in high demand and time in short supply. A working laboratory metallograph that can provide you with crisp, clear images and ease of use is essential. 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