Slide scanners how do they work

It is definitely no mistake if you make a copy of your image archive every years and still keept the old backups. If you don't trust external hard drives, we recommend to copy the DVDs with the image files regularly e. A blank DVD does not cost much any more nowadarys, and a future generation of storage media will compress the content of many DVDs on only one. If you scan a 35mm slide or negative with a resolution of ppi at a standard colour depth of 24 bit you will get an image file with approx.

This image file takes about 60 MByte. If you save it as JPG the image file shrinks to approx. However, if you open the compressed file in the image editing software it goes back to the original 60 MByte. So the JPG compression only saves space on the hard drive, not in the main memory when you open it.

In a time where each computer has a minimum of MByte main memory 60 MByte are quite manageable. Anyway, the necessary main memory demand can increasy rapidly if you execute image editing functions and filters. If you apply a filter on a 60 MByte image, the necessary memory may increase to a factor of 3 internal image duplicates, alpha-channels, space for computations etc.

On a PC with MByte often there are less than MByte left, since the operating system and other background applications use a main part of the memory. So a main memory of at least 1 GByte is recommendable. At high end medium format scans the image files are much bigger. If you scan a 6x6 cm medium format film with ppi and 24 bit colour depth, the resulting image file will bei approx.

For an effective image editing process of such a scan you require 1 GByte main memory minimum. If you process image files with 48 bit colour depth the memory requisition doubles.

For a comfortable image editing process of medium format films we recommend 2 GB free memory at least. Some user my laugh now, because his computer has a mulitple of the above mentioned memory demands. However, often you don't edit only one image at a time, but you load a complete series of images in the image editing software and want to edit them quickly.

If you load 10 or 20 images in your software you need a very large main memory, and an image editing program, which is able to use the provided memory at a time.

At analogue SLRs one can state that their development phase is finished, whilst the development of digital SLRs continuously goes forward. Of course digital SLRs are very sophisticated and offer an impressing veriety of functionality, however, every year new models come to the market, which outshine the old models clearly.

A couple of years ago even the best digital SLR could not keep up with the corresponding analog SLR in combination with a top film scaner. Nowadays the top models of digital cameras achieve values in terms of resolution and image quality, which had been achieved with the best analog cameras.

However, the top models of digital cameras are still extremely expensive. The resolution capability of analog films is limited by the film corn. But before this limit is achieved there is an other limit, namely the resolution limit of the lense, and this optical limit does not differ from the analog to the digital system.

What you make in the analog area by choosing the film speed you do in the digital area by setting the ISO nomber. Only the very expensive digital cameras have full format CCD chips in the 35mm format, which don't show essential noise effects at high ISO nombers, and only these CCDs in 35mm format use the full lense range and have no focal length increasment factor. The digital SLRs in the semi professional area do not achieve the quality and resolution of analog cameras in combination with very good film scannres.

But they catch up from year to year, and one day they will win that race. In earlier times nobody has thought about the resolution of a 35mm film. Nowadays many proud owners of a 10 megapixel digital camera wonder, how many pixels there are on an old 35mm film. One can answer this question by considering some data: A 35mm film has an area of 36x24 mm and a resolution of line pairs per Millimeter. A line pair is a pair of a black line next to a white line, i.

So line pairs correspond to pixels per millimeter. A normal 35mm with a resolution of line pairs per mm contains approx. If it has line pairs per mm this nomber goes up to 58 million pixel. A film scanner with an effecitve resolution of ppi extracts about 20 million pixel from a 35 mm film, and a good digital camera makes 15 megapixel. Does that mean that a 35 mm film is still unachievable for the digital photograhy? A 35mm film may contain 35 or 58 million pixel on one picture, however, the camera, which exposures the film with its lense, is not capable to distinguish the captured light rays so detailed.

The limit is the resolution of the used lense. Simple zoom lenses have a resolution of only line pairs per mm. High end lenses with fixed focal lense may have the double resolution. With 40 line pairs per mm only approx. This means that in most cases the optics is not capable the exploit the complete resolution capabilities of the 35mm film. The above mentioned of course also holds for digital cameras, since at digital cameras also the lense makes the picture, not the chip.

A 15 megapixel chip never makes 15 million different pixels, if you use a cheap standard lense. In the course of many years in the context of our Scan-Service we have made the experience, that a very good film like the Kodachrome film, which has been exposured with a very good camera and a very good lense, delivers approx.

This corresponds to a resolution of approx. How must a PC be equipped and configured for the user of a film scanner, so that scanning works without problems? We cannot answer this question flatly, since the requirements depend on the working fieldof the specific user. Most scanner manufacturer denote minimum requirements, so that the scanner and the scanner software work fairly. So your PC needs such interfaces.

If it does not have them you can extend your PC by corresponding PC cards. It is important to know that each film scanner, which is made for USB 2. For instance, if you scan a 35 mm slide with a resolution of ppi there will be 60 MByte transferred to the PC via the USB interface. Whilst this takes approx. Of course a USB 2.

That's why hardly a scanner manufacturer equips a scanner with a modern USB 3 interface. To the PC itself: If you think that a scanner delivers final images to the PC, which only have to be stored on the hard drive, you are wrong. Much more the scanner only delivery raw data to the PC, which have to be processed to an image file by the scanner software. So you have an advantage if you have a fast CPU and much memory. You should use at least a Core i3 processor if you don't want to loos much time; of course a Core I5 is better and faster.

A software which processes image files of 60 Megabyte in the 35mm field or even MByte at 48 bit colour depth requires a lot of main memory. The size of the hard drive is not important for the scan software, since it usually only takes a couple of MByte. Also, if you save your image files in the JPG format on the hard drive, you will net get into trouble due to the hard drive size.

However, if you save your images in the uncompressed TIF format or save even raw data, you need a lot of space on the hard drive. At a resolution of ppi scans need about 50 GByte on the hard drive if you save them in the uncompressed TIF format. If you edit high resolution scans in your image editing software you also need a fast CPU with much main memory. The main memory should be especially large, since the image editing software makes internal copies of the images and needs a lot of memory for applying filters and settings.

You don't need a high end graphics card, since normal image editing functions are only in the two dimensional field.

Modern graphics boards are optimized for the three dimensional operation mode. An important element is the screen: No matter if you use an old CRT or a stat to the art TFT screen, you should calibrate it with a hardware tool like the Spyder.

If you use a monitor which is not calibrated it shows all images in wrong colours. If you correct these wrong colours in the image editing software you correct the screen error indeed, and make the real images even worse. So the calibration of your monitor is indispensable.

These days most slides are put into plastic frames, which can be stowed well and sasavely in big magazins. However, there was a time, were glass frames were the top recommendation for slides. A main argument was that the film material was protected against exterior things like humidity and dust. But it turned out that glass frames offered more a short term protection than a long term protection, since humidity and dust, which attaches in the course of a long time between the film and the glass frame, causes much more damage to the film material than dirt which lies directly on the film.

If molds come up between the glass and the film, the film material often is affected directly. Which kind of frame is advantageous for scanning slides? Basically in the photography holds, that the reproduction quality of an optical instrument deteriorates with each glass plate or lense, which is used.

Each part of glass absorbes a part of the light or has errors reflexions, aberrations etc. This becomes very obvious in the photography when you compare lenses with fix focal distance with zoom lenses with lots of moveable lenses. Thus for scanning films you should use as few glass as possible. Because of that reason each flatbed scanner with transparency unit 2 glass plates used is inferior to a real film scanner, which x-rays the film directly. So it is also clear, that the image quality is worse at glass frames compared with plastic frames.

And the thicker the glass plates are the more light is absorbed. Dust, which lies between the glass plates, can be eliminated up to a certain level by hardware based scratch and dust removal procedures. Anyway you should clean the glass plates before scanning with a fine cloth.

Scanning becomes problematic when there are air bubbles or humidity bubbles between a glass plate and the film. These will be scanned exactly as you see them with your eyes. This looks awful at the screen and cannot be corrected, since the borders run right across the picture. In this case unly reframing in glassless frames helps. Another bad effect at glass frames are Newton rings. These are interference patterns which can be minimized, but not avoided, by using Anti-Newton glass.

However, there is one advantage of glass frames worth mentioning: Some very old slide has an extreme curvature on its surface. In a normal plastic frame it is not flat any more. At film scanners with a low depth of focus it may happen, that the image becomes partly unsharp due to the curvature. In this case glass frames have the advantage that they press the slide plain so that it lies flat in one level. In order to keep a slide flat in a frame there are a couple of special frames from a few manufacturers.

Conclusion: If you scan slides in glass mounts you must expect quality deficits. How strong these deficits are dependes on the condition of the glasses and the layer between the film and the glass.

Reframing brings a quality improvement in any case. For all optical instruments holds that the optical imaging performance deteriorates the more glass the light has to go through. Pulled from the shelves for infringing on Polaroid's patents, it's been all but forgotten, until now.

Want more photography techniques, camera reviews, and inspiration? Sign up for Popular Photography's newsletter and join the club. How to scan negatives using a standard scanner Everyday flatbed scanners don't work to scan slides and negatives because they need to be backlit — but with just a bit of cardboard, you can redirect some light, and make it happen.

A sample slide of a dancing dog. Here are some tips to help you get the best out of your digital pathology line scanner:. Here are some aspects of tissue preparation that can affect the digitization process.

To improve results with your slides, always check and clean them before scanning. Each digital pathology scanner model has its own workflow and requirements. However, there are some general guidelines to follow in order to get a good scan. Despite all your efforts, not every scan will be acceptable first time.

QC processes will vary per lab, and you should always follow the QC requirements of your institution. However here are some steps you can follow for quick and efficient scan QC in your image viewer. Follow these simple guidelines when scanning, to help you produce higher quality digital images and give you a permanent record of your slides that you can view, share, and analyze.

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