This feature aims to help you choose the right scanner and to get the most out of it, whether you are an amateur on a tight budget or a professional needing high quality for reproduction and sale. It looks at the main types of scanner, explains the significance of resolution, bit depth and density range, and looks at hardware and software issues.

Which type of scanner do you need?

If you are buying a scanner, the first thing you need to decide is what you want it for. Scanners can be used to scan prints and other flat art work, and also to scan film negatives and transparencies. They are also used to scan text so it can then be converted into editable files using appropriate software. More specialised usages are also possible, with some scanners being used to record both two and three-dimensional objects.

Scanners run in price from under $50 to more than $50,000, and not surprisingly their quality and facilities differ. The top-end models are largely used in publishing or by companies offering expensive scanning services, and this feature will concentrate on those more likely to be of interest to photographers.

Fortunately, the quality produced by the best affordable scanners can be very high, and scans produced from 35mm negatives and slides from the best equipment aimed at advanced amateurs and professionals can pass as 'drum scanned.' If you have high quality large format negatives the differences are still clearly evident in large prints.

Flat bed Scanners

A flat bed scanner is designed for scanning prints and other flat artwork. Most have a glass bed or 'platen' on which the original is placed, on the top of a box containing a light source and photosensitive receiver, usually a CCD array or a CIS (Compact Image Sensor), a single row of photocells. Older scanners were often monochrome only, but now all are 'three colour' RGB devices using separate photocells to measure red, green and blue light.

The print is scanned in a number of parallel lines, with the photocell moving along each line to record the light reflected from the print. The light source may also move or it may be a strip across the width of the scanner. Some scanners use a LED light source that can rapidly switch from red to blue to green, allowing a single row array to read all three colours one after the other. Others use a white light source with RGB sensitive cells in the array.

At the end of each line, a stepper motor moves the light source and receiver a small step across the print to let the CCD to read the next line, continuing in this way until the end of the scan. The resolution of the scanner in one direction is thus controlled by the closeness of the steps across the print. In the other dimension, the resolution depends on the spacing of the photocells in the array.

You can read more about how flatbed and other scanners work in the links to simple technical features at 'Howstuffworks' and 'Extremetech' - see box at top right.

Resolution

These two resolution figures give what is known as the 'optical resolution' of the scanner, usually expressed as two figures in dots or pixels per inch. So a typical flatbed scanner may have an optical resolution of 1200x600. There is a small problem with unequal figures like this, in that we need equal horizontal and vertical resolution for most image files. The scanner software can either sample down the higher figure to give 600 ppi, or extrapolate the lower figure to produce 1200 ppi.

Although there is little practical advantage (and the disadvantage of doubling the file size) not surprisingly the marketing departments of scanner manufacturers prefer the second approach. Often they take this further, by providing a software option that will increase the apparent resolution, perhaps to 4800 ppi. Should you ever have a need to do this, there is software that will do a better job than the scanner software. So always ignore any figures higher than the optical resolution.

Resolution is seldom important if you are buying a scanner solely to scan prints. You will seldom if ever want to use more than 600dpi for this purpose, and most scanners provide this. You will want higher resolutions if the scanner includes an option for scanning transparencies (see the next part of this feature.)

复 d vs film/slide

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【文摘】Scanner Features

Scanner Features

Bit depth

Its continuous voltage readings are converted to a digital signal for output. This analogue to digital conversion usually produces a signal of between 8 and 16 bits for each of the three channels, 8 giving 256 different values and 16 giving some 65 thousand for each channel. Most current consumer models can distinguish somewhere between this number of levels, producing 10, 12 or 14 bits per channel. So long as the software can make use of these, a greater number of bits means better images.

Density Range

Different photosensitive cells in use differ considerably in the range of light values they can detect. This is measured as the density range or optical density. In general, higher figures make for better scanners, but the methods used to measure these by different manufacturers are different, and comparisons between them are doubtful.

Scanner software

The software supplied by the manufacturer for you to use the scanner is often in the form of a twain or similar driver that will interface with your imaging program. In general manufacturers of consumer scanners seem to put little effort into providing software that enables you to get the best from the scanner.

Some scanners come with third party scanner software that does a better job, or you may be able to buy this yourself. This is generally more necessary if you want to scan film rather than prints. Find out more about this in the last part of this feature - Scanner Software - see box at top right.

Descreening

When scanning pictures from books and other printed material there is a problem because these images are generally printed as dots in a regular pattern. Because the scanner looks at points also in a regular way, there is always some interaction between the scanner and the dot screen, resulting in a pattern effect known as 'moiré'.

This interaction can often be reduced by placing the image so its edges are not parallel to the platen edges, but at perhaps 15 or 30 degrees to it. If you plan on scanning much material from printed sources you should also check that the supplied software has a 'descreeening' option, preferably with settings for different qualities of print.

Flat bed sizes

Most consumer flatbed scanners have a platen that will scan an A4 page. There are some smaller scanners intended for scanning photographs up to 6x4" only.

A3 (and even larger) scanners are also available. There are some which are basically A3 versions of consumer scanners and available at reasonable prices. High quality large flatbed scanners, such as the Creo-Scitex range (at very high prices) are also used to produce repro-quality scans.

Flatbeds and film

Some flatbed scanners can also scan transparent media, such as slides and negatives. This requires an alternative light source, either in the lid of the scanner or in a special 'transparency adaptor' attachment that needs to be fitted. The light shines through the film onto the photosensitive receiver.

The transparency adaptor may limit the size of film that can be scanned. Some are very small and only scan a single frame of 35mm film, while others will take sizes up to 4x5". With some scanners, the whole area of the platen can be used, and in some expensive high-end devices, there is a scanning light-source on one side of the film and a scanning receiver on the other.

With some scanners there is a small area of the scanner that can be used at a higher resolution than the rest of the platen especially for film scanning.

From cheap consumer scanners, the results from 35mm film are generally poor, but may be good enough for low quality images on the web. They are likely not to make very good prints.

If you use medium format film, a suitable transparency adapter can give reasonable prints, but the scans are still generally not up to the level of a good film scanner - but then nor are the costs.

The best film scans I have ever worked with have come from a high-end flatbed scanner. The differences between these and scans from a good drum scanner in a similar price range are immaterial.

复 d vs film/slide

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【文摘】Film Scanners

35mm Scanners

Film scanners aimed at amateur and professional photographers are mainly for 35mm slides and negatives. Film scanners use a light source on one side of the film and the photosensitive cell on the other. In most the film moves across to produce the different scan lines, though some work by moving light source and cell as in a flatbed.

Most will take slides in normal mounts, as well as strips of negatives and transparencies. A few models only will cope with negatives longer than the standard 36mm, so if you use a panoramic format camera such as the Hassleblad XPan, your choices will be limited. Some come with holders that will take APS.

Input resolution

Since the original is so small, film scanners need higher resolution figures than flatbeds which are generally used with large originals. A rough guide to the resolution you need is given by multiplying the smaller dimension of the print by 300. So to make 8x10 prints, a resolution of 8x300, which is 2400 ppi, is satisfactory.

You can make bigger prints than this suggests, but the quality will not be optimum. For professional use, a resolution of 4000 or 4800 ppi is probably essential.

The quality of scans produced from film scanners is very dependent on the light source, the optics used, the mechanical design and build quality, and in particular on the design of the slide or negative holder. It is not surprising that the best-known makes in cameras are also some of the best-known in film scanners, including Minolta, Canon and Nikon. Microtek have also made some good film scanners, both under their own name and also for Polaroid and other companies.

Medium Format

Medium format scanners can also scan smaller sizes such as 35mm. Not surprisingly, they are larger and more expensive than 35mm models. A lower resolution is fine for scanning larger negatives - few purposes will need more than 3600 ppi from 120 film.

One of the most affordable of these is the Minolta Dimage Scan Multi Pro, which attracted some lukewarm reviews when first introduced. Many of its apparent shortcomings were shown by users to be caused by the software, and an active Multi-Pro User Group prodded Minolta to make improvements. With the new software, it is a much better piece of equipment, although third-party software will still generally get more from it.

Software Problems

Many of the problems photographers have had with scanners come down to a perception by manufacturers of them as 'slide scanners'. Most photographers prefer to shoot on negative, and many have turned to scanners as a way to enable them to do so, while providing clients with positive images on CD-R. Although negatives are actually easier to scan because the densities are less extreme, both the hardware and the software needs to be geared to this use.

The solution favoured by some manufacturers has been to include third party scanner software, sometimes charging a premium price for it. The well-regarded SilverFast software (see below) has been included with some 35mm scanners from Nikon and Microtek. Many users have also turned to third-party software, including the relatively inexpensive Vuescan, covered in detail in the last part of this feature, Scanning Software.

复 d vs film/slide

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【文摘】Film Scanner Problems

Film Scanner Problems

Holding film flat

When scanning film, one major problem is in holding the film flat. Designing good negative carriers is surprisingly difficult, and all of those I've used have their problems. Slides are often scanned in their mounts, and only glass-mounted slides are ever flat across the whole slide.

As with enlargers, few negative carriers are designed to show the entire negative frame, giving slight cropping at the edges. If you want to scan full-frame you may need to perform some very careful opening out of the apertures with a suitable tool. Getting replacements for negative carriers should you damage on can be a lengthy business. I've had one on order from the UK distributor of my film scanner for several months with no success. Fortunately I still have one in working order and am waiting for the replacement to modify for panoramic scanning.

Glass or glassless film carriers?

Using glass in a film carrier also improves sharpness, but at the expense of adding 4 surfaces to keep clean and dust-free. If clean, they may also produce interference patterns - called 'Newton's Rings' with the film base in close contact, and are sometimes produced with a finely ground surface to prevent this, which may add a very slight texture to the images.

Dust Problems

Dust is a major problem in scanning, more so than in enlarging because most scanners make use of highly focussed point light sources which show off every blemish. If you've ever used one of the fairly rare point-source enlargers you will be aware of the problem. Diffuser enlargers make life much easier in the darkroom.

A typical high resolution scan from 35mm - even if care is taken in cleaning the negative and carrier glasses (if used) may take 25 minutes work to clean up and remove all blemishes. In Photoshop the healing brush and the clone stamp are the main tools to use. Anything that can reduce this amount of work is important.

Diffuser

Recently two leading members of the Minolta Dimage Scan Multi-Pro user group came up with the simple idea of adding a diffuser to the negative carriers of this scanner. The improvement it gives is impressive, not only in reducing dust but in giving less 'noisy' scans but retaining the same level of detail. The Scanhancer they designed is available cheaply. Although it is specifically cut to size for the negative carriers for this scanner, it may be worth trying the same principle with other scanners.

Minolta have independently been working on the same principle, and have incorporated it in their latest 35mm scanner, so you can expect this to become common practice. Other scanners may already be designed to have a diffuse light source, and so avoid the worst of the problems.

Digital Ice

Another clever aid in beating dust is the use of an infrared scan channel. Infrared is little absorbed by the dyes in most colour images, so produces an image that is mainly due to dust and other film blemishes. Software can then be used to subtract this noise signal from the other channels. Digital Ice is very effective, but only works with colour films, and cannot be used with Kodachrome. You need to be careful in using it, as excessive filtering will also remove image detail.

Dust and scratch filters can be designed in software, but their use is limited as if applied strongly enough to remove most dust they also get rid of much image detail.

复 d vs film/slide

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【文摘】Drum Scanners

Drum Scanners

Generally drum scanners are of an impressive size, and correspondingly expensive, costing around as much as a car or a small house. These are used by pro labs to scan your film, so it is hardly surprising that a high resolution scan can cost $50 to $100 a time. The drums used are typically a metre or so long, and a number of images are scanned at the same time, each negative being held on a small part of the drum's surface.

The light source is in the middle of the drum, and the photocell outside. As the drum rotates, it scans every point on a circle around it. The light and photocell then move a fraction parallel to the axis of the drum for the next line to be scanned. The curved drum keeps the film to light source distance constant, and avoids problems with reflections.

Oil Mounting

Dust and most of the surface defects such as scratches on film become invisible if the slide or negative is immersed in suitable oil with a similar refractive index to the film. This is a technique much used on drum scanners and high-end flatbeds.

Removing the oil after scanning can present some problems, but is generally faster than the time otherwise spend in retouching to remove the dust. The oil also ensures good contact with the drum.

The best drum scanners can give scans as good as the best high-end flatbeds, and generally better than those from most film scanners. However, if you use 35mm film and the one of the better film scanners, the differences may be hard to discern.

Virtual Drum Scanners

Imacon scanners use what they call a virtual drum. In these scanners, the film is curved by applying a slight pinch across it. This creates perfect flatness along the film at right angles to the curve, and Imacon claim it gives the advantages of a drum without the size and cost implications.

The cheaper scanners in the Imacon range are popular with some pro photographers, claiming to give drum scanner quality at a much-reduced price. It is always difficult to assess such relative claims, especially without being able to work extensively with a wide range of expensive professional level scanners.

However, there is no doubt that the Imacon range is competitively priced and can produce good results. They are also much smaller than a drum scanner, which may be an important factor.

Which scanner should you buy?

Your choice of scanner type may be largely dictated by your budget. If you are an amateur photographer, you may find a flatbed with a transparency adaptor does all you need, or you may consider having both a flatbed and one of the cheaper film scanners.

Professionals are likely to find that their needs are met by one of the better film scanners, especially one of the medium format models from Nikon or Minolta. Scans from these are generally perfectly acceptable for reproduction purposes, so long as you learn to use them effectively. If you don't tell people they are not drum scans, they will probably never know. You will probably also want to get one of the better consumer flatbeds for scanning occasional prints, possibly with a transparency adaptor for rough scans of 4x5" films.

If you are using large format, then for professional use you will want a drum scanner or high-end flatbed (or possibly a virtual drum.) Unless you are part of a larger studio setup you will probably find it preferable to have you scans made for you. If you intend to buy a scanner, you need to study the available information on these carefully and to get examples of your work scanned on the machines you are considering buying. The prices for the best drum scanners such as those from Heidelberg get pretty elevated.

As for which make you should buy, this is harder, as it depends on your exact requirements. I've bought and used scanners from HP, UMax, Microtek, Epson, Canon and Minolta and have generally been happy with all of them. If I was replacing my current flatbed I would probably buy another Epson, but that doesn't mean they are any better than those from other manufacturers.

Were I to suddenly come into large amounts of money, and be able to set up and maintain an expensive studio full of equipment, the scanner I'd be interested in would be the Creo-Scitex Eversmart Supreme, an A3+ flatbed which scans at 5,600 ppi and has a density range of 0.3 to 4.3, but costs rather more than my annual income.

复 d vs film/slide

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【文摘】Scanner Software

Scanner Software

Software from different manufacturers generally provides similar features but may look rather different. There are two programs from independents I recommend for use with film scanners.

If you want to be able to scan from your transparencies and produce good quality 24bit images more or less automatically (once you have set up the process), then there is little reason to look further than Silverfast AI, if it supports your scanner.

If your main interest is in scanning negatives, then you may find Vuescan gives the best result, although you can expect to do a little tweaking of its 16 bit scans in Photoshop or your favourite graphics software. Before buying any film scanner I'd advise checking that it is on the list of around 200 scanners Vuescan supports.

How to get the most from your scans

You can check you are getting the most from your scanner and the software provided with it by downloading a trial version of Vuescan, available for both Windows and Mac. This installs in its own folder and makes no other changes to your system, so is easily be removed if you decide you want rid of it. The trial version produces scans with an intrusive overlay, useless except to compare with scans from the manufacturer-supplied software - exactly what you need to do.

Setting up Vuescan

Vuescan has an off-putting interface, with many settings on the half-dozen tabs which display on the left of its window. By default it hides many of the settings, but gives you a button to click to show all. It should detect your scanner, and the first settings on the Input tab to select media type, resolution and frame number are obvious.

Still on the Input tab, I normally select the 'Scan from Preview' option, which speeds up scanning by making only one pass across the film. Obviously you need to set the preview resolution at the output resolution you require when doing this. You should normally also choose to focus on preview.

For most of the other settings you can start with the default values, although you may like to go to the Color tab and select the actual film type in use if it is one of the listed options. For films not included (and the list is now in need of updating) either choose a similar film or the generic settings. (Vuescan Professional can also make and use an IT8 film profile if you have a suitable target to scan.)

Although some find the interface confusing, it is very logical, and to choose the directory to output your scans, you go to the Output tab.

Scanner Calibration and Preview

You are then ready to calibrate your scanner. Go to the Scanner menu at the top of the window and choose calibrate. While the scanner performs this, you can put your negative into the carrier ready to make the scan. Once the calibration is finished, insert the carrier and select a preview - the button at bottom left is convenient. This is actually the final scan if you have selected 'Scan from Preview' as suggested, so it will take a while before the preview image appears.

Changing the Preview

Start by checking the preview image and make any necessary adjustments to the brightness setting, (on the Color tab, choose 'All' under More Options if it is not visible) although the auto-exposure is usually fairly close.

Accurate focus is obviously vital for good scans. An advantage of previewing at the scan resolution is that it enables you to zoom into the preview image and check it is sharp. You may occasionally find that scanner software fails to focus correctly, perhaps because there is no suitable detail in the area picked for focus. If this happens with Vuescan, simply drag the focus indicator to an important part of your image and repeat the preview. If you didn't select auto focus on preview, you will need to focus manually first using the Scanner menu.

Using the histogram

The basic tool for understanding what your scanner is doing is the histogram. Look at it using the 'Preview hist' tab above the preview image. The histogram represents the tones in your image as a bar chart, from dark to light. For colour images you can see the three colours separately, but generally it is enough to look at the combined RGB curve. The example shows the very clear view histograms from Vuescan.

Preview histogram display from Vuescan.

点看全图

外链图片需谨慎，可能会被源头改

The curve should start at zero at the left hand axis (black) and finish at zero at the right hand axis (white.) If there is a gap between the axis and the start of the curve, you should increase the black point setting, while a gap at the right end of the curve means the white point setting is too low. The controls for making these changes are on the Colour tab.

For this particular image, my usual settings were pretty close. The Vuescan default settings give considerable more white point clipping than I like, and a figure close to zero works for most of my negatives. The histogram shows a small amount of clipping at the left hand side (black) where the blue and green curves have not quite dropped to zero, although they are very close.

If the curve does not fall more or less to zero at either end, even after you have adjusted the exposure and black and white points, then the image you are scanning has a greater range than your scanner can handle. This can happen with some overdeveloped or overexposed materials. Some scanners can handle a greater range if you scan negatives as slides. Unless you make the histogram fit the chart properly you will not get a high quality scan.

Final touches - EditLab 4.0

You can make other adjustments to your scan in the software, but if like me you like to finish the process in Photoshop, then so long as you fit the histogram and output in 16 bits per channel, there is little point in doing more at this stage.

Editing of 16 bit images can be done more or less without loss, while when you only have 8 bits to work with, it is easy to get images that show clear jumps in tones as adjustments tend to reduce the total number of colours.

点看全图

外链图片需谨慎，可能会被源头改

You never know quite who you will meet in South London. 21mm, Hexar RF.

This is the image whose histogram was shown above, after a couple of tweaks with EditLab 4.0.

Vuescan handles colour balance automatically for both positives and negatives. With some other software you may need to adjust the colour balance, perhaps by selecting a neutral tone in the image. The problem is that many images have no true neutral, or there are several possible candidates that give different results. Vuescan generally does a good job, but is not always perfect.

I prefer to let Vuescan do its best, then to balance finally in Photoshop, preferably using the Pictographics iCorrect EditLab 4.0 plugin which usually gets a great balance with minimal effort, even for those tricky images. It does a great job, not just of correcting neutrals, but also allowing you to match reference points such as flesh, foliage and blue sky for both hue and saturation. The jpeg shown here is not quite the same colour as the tiff file, which has good neutrals.

Buying Vuescan

Vuescan is software sold online by its author, Ed Hamrick. Its sales have built up over the years largely through word of mouth among those of us who scan negatives. Most of those who tried it bought a copy immediately, as I did. It is now available in two versions, Standard and Professional, with the professional version adding support for ICC profiles, raw scans and IT8 colour calibration and a year's free upgrades (they come fast and furious, but only take a few seconds to download and install.)

Some of the upgrades add fix bugs; others add new features or improve the existing ones, often in response to user suggestions which the author obviously takes very seriously. Unlike most other scanner software, Vuescan is a standalone program rather than a twain module. This means you can happily keep on scanning images in one window while using your graphics software to edit in another, although since both can be very processor intensive your work will slow at times. Although not the absolute bargain it used to be, Vuescan is still a very useful piece of software.

复 D70 VS D100

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都是些理论上的指标,但是片子不光看指标

一样的场景,两张片子,给再外行的人来看还是会感觉FILM的舒服点

复都是些理论上的指标,但是片子不光看指标

家园

俺早就发现了，无情是个顽固的保皇党、复辟狂……

坚决拒绝大势所趋的人民大众的数码拍照洪流，仍然紧抱着他那小资产阶级的传统相机不放………… 大家擦亮眼睛啊！！！

复编号是从大往小编吗？

家园

尼康的规矩一般是

同一系列里面数字越大的档次越高。如最高端的专业胶片单反F1、2、3、4、5（据说明年要出F6，而且可能是尼康最后一个胶片单反）；然后是从普及型的F50、55、60、65、70、75到准专业的F80、90、F100。现在是数码高端产品D1、D2和准专业系列的D70和D100（相对于其胶片单反F70和F100）。如高兄所说，虽然D100理论上比D70“高档”，但由于D70后出，所以不少指标反而胜出。

佳能的规矩是数字越小越专业（EOS系列）。但它碰到问题了，因为EOS1早就出来了，然后还怎么发展啊？于是后来就有了1N，1V等等……迷糊。

复都是些理论上的指标,但是片子不光看指标

家园

我只喜欢金属相机的感觉,连照片是啥样都不管了.

不敢逛二手机相机店,总是想把玩一番....

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