Scanning - The scanner article

Digitising Negatives and slides

Scanning

Scanners work by sampling an image via a row of photo sites which read an image one ‘row’ at a time. The row of photo sites can move over the target, or the can be moved relative to the target. Scanners are usually lit from the front for reflective material (prints/documents), but transparent materials such as negatives or slides need to be lit from behind to give them adequate illumination.

As it works one line at a time, scanning is relatively slow, but can give very high quality results: compared to a normal Bayer camera sensor there is no interpolation as scanners typically have a row of photo sites for each colour, or alter the emitted light to get three separate samples.

Copying

Compared to scanning, copying is a relatively instantaneous process which involves projecting an entire image on an imaging sensor with a Bayer filter array. Copying can be achieved with a macro lens on a camera, a dedicated slide/negative copier for a camera, or via a unit which is effectively a small captive camera.

Resolution for scanners

Scanner resolution is usually quoted in ppi (pixels per inch) and is determined by the number of photo sites across the row in one direction and the distance that they are capable of being moved accurately relative to the target in the other. This means that resolution is fixed in one direction (typically the width) but can be varied in the other; for this reason resolution in the longer direction is normally quoted as a higher figure: beware of this as the lower figure will be likely to be the 'true' resolution. Also be wary of interpolation as this will get you bigger file sizes but not greater quality.

MiPr wrote: ...may I add a note about the resolution of scanners? Generally it's all bulls... far from being true. For example CanoScan 9000f, which is advertised as being able to work at 9600 PPI in reality achieves ... 1700 PPI (the "sweet spot" being when it's set to 4800 PPI). Same thing is for all scanners, including dedicated film scanners although they usually have much better BTRR (bulls... to reality ratio ).

Sizes of resultant scans

Typical resolutions for film scanners are 2820, 3200, 4000, 4800 and 5400, although some older models may only be 1200ppi. Because the typical 35mm negative is 24x36mm, the sizes of the output files are as follows:




Note that the file size generated from scans can be quite large – a DNG RAW file from a 2820 single pass colour scan can be over 28MB.

It used to be said that the detail in a film negative was roughly equivalent to a 14MP sensor, which would fit in with the old maxim that you could blow up a 35mm negative to 8x10 quite comfortably.

Types of connection

The type of connection affects speed of scanning.

Parallel ports used to be available on PCs as a way of connecting peripherals like printers and scanners; no longer common and rather slow. A parallel connection may require the scanner to be connected at boot-up.

SCSI connections are fast, but require a card to be fitted – the ones likely to be most compatible can also be quite expensive. A SCSI connection may also require the scanner to be connected at boot-up.

USB 1 is plug and play, is compatible with most modern PCs/Macs, is easy to use, but slow in comparison to SCSI, Firewire and USB in higher versions.

Firewire is also plug and play, is fairly widely available and a little bit faster than USB 2.

USB 2 is plug and play, is available on most desktops and laptops and is pretty fast (so much so that you don’t see a lot of USB 3 scanners).

Dynamic range

Dynamic range is an important consideration for any photographic device; for scanners this tends to be expressed as DMAX, although more properly we should be looking at DRANGE (DMAX minus DMIN). The higher the quoted figure for DMAX, the more shadow and highlight detail the scanner should be able to bring out from a single scan. Bear in mind that most negatives will be fine with a DRANGE of around 2.8, which is covered by most scanners. Even slide film should not need much more than 3.2, although some ‘difficult’ slides might need more. There is a lot of cynicism regarding manufacturers DMAX figures and at some points DMAX may have been used in a similar way to megapixels – more does not necessarily give you better results.

Ways of increasing Dynamic range

The dynamic range of the image can be increased by taking multiple exposures and merging them to produce an HDR picture. In a similar way a scanner can do multiple passes that will capture shadow and highlight details. In some cases the original controlling software allows you to perform these multiple exposures, but third-party applications such as VuScan and Silverfast may enable multiple exposures even if the original software does not support it. The key attribute of a scanner here is that it should be able to reposition and control the movement during the scan well enough to allow accurate registration.

Colour depth

RGB JPGs are typically 24 bit – 8 bits for each of the component colours (256 possible values apiece) giving over 16 million colours in all – more than can be perceived by the human eye. Scanners can gather far more information about colour transitions in 36 bit (12 bits per channel) or 48 bit (16 bits per channel). In converting to a printable or viewable format, a lot of this information will be discarded, but having more information available gives some choice about what information we discard – so more is good, but comes at a price (file size) and may not be able to be perceived in the final output.

Focusing

Fixed focus

Many scanners, particularly flatbeds, rely on the fact that the target is flat and at a known distance from the sensor. Differing thicknesses of mounts for slides and even curl in film may affect critical focus.

Autofocus

Many, but not all, dedicated film scanners have an autofocus feature which will assess focus prior to a scan; by default, the autofocus target is usually the centre of the frame/negative (which is where any curl is likely to be most pronounced), but some scanners may allow choice of focus point or manual adjustment of focus via software (this is the sort of feature that may only be available using the original software).

Manual focus

Some top-flight flatbed scanners feature adjustments for focus via feet on the negative/slide holders. For scanners that do not offer this feature it may be possible to substitute third party holders that do, or to shim existing holder to get the desired levels of focus. Getting accurate manual focus in this way can be laborious.

Scratch removal

Negatives and slides are small and tend to attract dust and scratches which are then magnified in the scanning/enlarging process; good practice in handling and preparing negatives may minimise problems, but any small scratches and dust will still show up in output images and may require extensive ‘spotting’ during post-processing.

Automatic scratch removal works on the principle of finding out what dust and scratches are present during one scanning pass and removing those from the eventual output through a subtraction process. This is done by scanning the film with an infra-red light source which will pass straight through the image dyes on a negative or slide as if they were transparent, but will be absorbed by scratches and dust. There are a number of variants on this technique one of the best regarded of which has been ‘Digital ICE’. If you do lots of colour work having a scanner which can do an infrared pass is likely to save you lots of time.

Where automatic scratch removal doesn’t work

Unfortunately, while the dyes used in colour processes are invisible to IR light, the silver grain of most black and white films, and the cyan dye used in Kodachrome, are not - so scratch removal will not work on typical home process B&W films. Various manufacturers have managed to get their systems to work on Kodachrome, but there may still be issues. C41 process B&W films where the silver salts are replaced during processing by dyes, should be able to use digital ICE, but you are likely to have problems with anything that you can develop at home.

Bulk scanning

Digitising an entire archive of negatives and slides is a big job and borders on the impractical: Scanning in bulk gives you relatively little opportunity to bring out the best in each negative. Scanning in ‘RAW’ mode, or with multiple exposure passes may give a fair amount of elbow room for later work without having to re-scan, but this is likely to increase scan times.

For most film scanners, ‘bulk’ means a strip of six 35mm negatives or of four slides in mounts (less if dealing with medium format); even then a film scanner needs a motor of some kind to drive successive frames past the imaging sensor, or requires a flatbed with a large film scanning area and a suitable negative holder. If you are dealing with APS negatives, you can get attachments for some film scanners that allow scanning of an entire roll at a time, but the adapters are neither common nor cheap.

Colour casts

The film base for colour negatives tends to be an orange-yellow which can make getting a good colour profile problematical. Software may allow you to specify the producer of the film, for which it will make a specific compensation.




Edited by Bob J - 18 March 2020 at 12:44

Comparison of cheap film scanner (Minolta Dimage Scan Dual II), cheap flatbed (Epson Perfection v350) and copying via camera (Sony a99 & 100 macro) - Now updated to include a comparison with a Minolta Dimage Scan elite 5400 (many thanks to Xavier for the loan of film and slide holders to make this comparison possible)

Comparison of muli-pass scans from DSII and v350 taken via VueScan with a camera shot.

Whole picture:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


Histograms:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


100% crops:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


Single-pass scans from Dual Scan II and Epson v350 compared to camera copies

Whole negative:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


Histograms:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


Crops:

Minolta Scan Dual II


Konica Minolta Scan Dual IV


Minolta Scan Elite 5400


Sony a99 & 100 Macro


Epson Perfection v350


Exposure:
Note that, straight out of the box, the Scan Dual appears to be exposing for highlights while the Scan Elite is giving a wider range of tones and the Epson seems to be exposing for the shadows; not too much of a problem as both are RAW files and probably contain a reasonable amount of headroom, plus you can adjust exposure at the time of the scan to favour shadows or highlights. The results from the camera are quite impressive, but a bit noisy in the shadows (ISO 800) when viewed at 100%.

Sharpness:
The AF of the Minoltas seems to be a big advantage here - with even the Scan Dual cancelling out the extra resolution of the Epson - however other flatbeds might have better focus.



Edited by Bob J - 18 March 2020 at 13:10

Thank you, Bob!

It seems you have spent a lot of time and effort in putting this article together! It is very much appreciated and hopefully it will answer many questions Dyxum forum members may have on digitizing negatives and slides.

More good scanner reviews can be found here: Shutterbug Magazine Scanner and Printer reviews

I'm not real familiar with Ken Rockwell, but he seems a little wacky. Is he always like that?

I'm also not well acquainted with Vuescan. The Camera Raw Lab illustrations are from Vuescan?

Thank you again!

Regards,

Kelly



Edited by AudioDoc - 12 March 2014 at 20:00

I used to have Epson V750-M (flatbed scanner) and Nikon CoolScan 5000 ED (dedicated scanner). Now I have Nikon CoolScan 9000 ED.

I don't think I can have a fair comparison between the flatbed and the dedicated scanner. I feel that I've never managed to get the best out of the flatbed scanner due to 2 main reasons: 1) I couldn't keep the negatives (especially medium format) flat, 2) I couldn't get good results with the software (SilverFast and VueScan). With the Nikon scanner it is much easier to keep the negatives flat and I think I have a good control using the Nikon software.
I will try to see if I can find frames that were scanned with both scanners and I will post the comparison, but again, the main differences are going to be my technique rather than the scanners. On the other hand, it brings up one advantage of dedicated scanner - easier to keep negatives flat...

Thanks for your valuable information Bob.

Without knowing this thread existed and without giving it an in-depth evaluation I bought a Canon Canoscan 9000F mk II (reasonable reviews, good value for money). I'll use it to scan 35 mm film (positive and negative) for posting in Dyxum Film Challenges.

At 2.5 kg it turned out a fair bit heftier than expected. looks and feels well made. The various holders for film work well but the 35 mm negatives are only supported at the perforated sides and I can imagine flatness is an issue. I am thinking about DIY film support improvements.

That brings me to scanner software. Non-intuitive interface, meaningless icons. Found out how to make it scan 3200 dpi TIFF (48 bit colour, 16 bit B&W) and left it at that. Ignoring warnings about how 100+ MB file size could crash your computer it scanned without problems to 15 MB files.

A bit underwhelmed about the 1st film (B&W) scanned. Didn't know what to expect. After rescanning with better light adjustment (also here the canon software has dubious interface), dust removal in LR4 and resizing to 1024 wide they look OK.      

I've updated the above to include links to Luminous Landscapes' Scannerless Digital Capture and Processing of Negative Film Photographs by Mark Segal and Todd Shaner in November of 2014. Looks to be well worth a read.

Mark Segal has now published The Epson V850 Pro Scanner in Context in The Luminous Landscape. He has compared the new Epson to older scanners, (e.g. Epson V750, Plustek OF120, Nikon 5000, Nikon 9000, Imacon, Minolta 5400) in an 89 page PDF which makes for interesting reading.