How Do I Digitise Difficult Objects?

Last updated: 03 March 2010
Published in: Digitising analogue media | Creating new digital media |
Tags: analogue collections | bit depth | cameras | digitisation | equipment | hardware | optical character recognition | photography | scanning |

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Scanners and digital cameras are the most commonly used devices for capturing still images; the digital files they create fit seamlessly into the modern workflow. This document looks at scanners and digital cameras and how they can be used to capture non-typical objects. In this document we look at a range of different objects and how we can capture them with a camera or scanner and a few accessories.

This document is aimed at users who have to capture difficult objects occasionally rather than on a day-to-day basis. If this is a task that has to be undertaken more frequently then a more advanced solution may be required.

Introduction

In the early days of desktop digital imaging, scanners were exotic and expensive devices which were normally used to capture a low quality ‘rough' or ‘scamp' images that would be dropped into a document layout. A skilled scanner operator would then replace the rough with a high quality drum scan. Over time scanners have become cheaper, quicker and much, much better. Scanners are now familiar desktop devices both in the office and at home.

A few years ago high quality digital cameras were also very expensive pieces of equipment used mainly by professional photographers and wealthy amateurs. Recently however affordable cameras have flooded the market and have all but replaced film cameras.

With a basic understanding of the operation of the camera or scanner the user should be able to effectively digitise a wide variety of objects.

Before we look at some examples it is important to understand the features of the tools we are using. If you would like more information, you could read our documents on Scanners or Digital Cameras.

Before you embark on any of the methods detailed below it is essential that you check that by doing so you will not be breaching copyright.

The scanner

The most commonly used scanner is the flatbed, this has a large (A4+) glass plate onto which the original artwork is placed, and below this there is a light source and a moveable linear CCD sensor. There will usually also be a light source in the lid which is used to backlight transparent materials such as negatives or slides.

The scanner's sensor passes below the artwork as it scans, this may take a few seconds or over a minute depending on the size of the original and chosen resolution. If the scanner is used to digitise objects and deliver them at a similar size to the original then an optical resolution of between 300ppi and 1000ppi might be used. If the aim is to capture objects and then use the images significantly larger than the original then a much higher optical resolution should be used. Scanners offer a maximum optical resolution and a higher yet inaccurate interpolated resolution, it is important that the operator doesn't choose a resolution setting higher than the maximum optical value as this only creates larger file sizes without an increase in quality.

Another important factor to consider when choosing a scanner is its dynamic range, this is a measure of the scanner's ability to capture a wide range of tones from black through to white, generally speaking the higher this value the better the scanner.

The scanning software may be able to remove or reduce flaws such as scratched negatives or Moiré patterns though this will increase the capture time.

Scanners are normally operated from a tethered computer connected via USB or Firewire cables.

While A4 is the typical scanner size there are a handful of models, which can scan larger areas though these are usually more expensive and tend to offer lower maximum optical resolution values.

Flatbed scanner

The digital camera

The limited maximum object size and controlled lighting of the scanner is not a factor for digital cameras and they can be used to capture both 2D and 3D objects.

Most cameras have onboard storage and a power supply and can be used tethered to a PC or independently.

With the correct accessories a digital single lens reflex (SLR) can photograph a huge range of subjects from microscopic organisms to distant planets.

The two main types of digital camera are compact cameras where the lens and camera are incorporated into a single portable unit and SLRs where the lenses are detachable; the user chooses a lens appropriate to the given task. Compact cameras are quite capable of delivering high quality results though SLRs offer greater flexibility.

SLR camera

When choosing which focal length to use on a compact camera or separate lens to use on an SLR, it is essential that you understand how the focal length contributes to the appearance of the final image. Wide-angle lenses (lower focal lengths in milimetres) capture a wide field of view, which may introduce 'barrel' distortion to a subject. Telephoto lenses (higher focal lengths) may require a greater working distance, they are less likely to introduce distortion but the depth of field will be shallower.

When I scan from a book or magazine a nasty pattern appears over the picture, am I doing something wrong?

Most colour or greyscale pictures in books or magazines are printed using a pattern of printed dots known as a halftone. When a half toned image is scanned the halftone pattern interferes with the pattern of the pixel matrix to create a third pattern, this is known as ‘Moiré'. It is normally possible to reduce the Moiré pattern at the point of capture.

Left, image scanned from book. Middle; close up of image showing Moiré pattern. Right, the same image scanned with descreen switched on.

You will need

• Flat bed scanner
• Well-featured scanning application or image optimisation application

How to do it

1. Place the artwork in the scanner
2. Open your scanner software
3. Choose the advanced mode if available
4. Click Preview, may also be called View or Prescan
5. Choose the 'Descreen' and pick the setting which best describes your artwork.
6. Check the image and save if you are satisfied.

If the scanner software does not offer descreen some image optimisation applications offer descreen filters or there may be simple workarounds. It is important that descreen is only used when scanning halftone originals, descreening will degrade the quality of scans made from continuous tone originals such as photographs or paintings.

How can we light a watch or coin to avoid nasty reflections?

Coins, medals or watches or other small shiny objects are notoriously difficult to photograph. The challenge is to get the camera and light close enough to the subject without them interfering with each other.

If the camera's built in flash is used it will probably cast a shadow of the lens onto the object. If the light is placed to one side some details may be lost in the shadows or highlights. The most effective way to light a small reflective object is by lighting the object as though from the centre of the lens, this is called axial lighting.

Left, coins illuminated from one side. Note strong shadows and lack of surface detail. Right, coins illuminated with axial lighting

You will need

• Clean sheet of glass of around 10'x 8' in size for the typical coin, medal or watch
• Black velvet or cloth
• Tripod with vertical bracket, or copystand
• A true macro lens (at least 1:1 magnification ratio) or close up filter
• A bright directional light, a desk light can be used though the exposures will be longer

Typical axial lighting setup

How to do it

1. This set up is quite complex and requires a darkened environment with enough space to move around the subject
2. Choose a flat base or table around 50cm from the ground
3. Place the camera on the tripod or stand pointing down at 90 degrees onto the table (check with a level if necessary)
4. Spread the black material across the table to absorb reflections and other stray light
5. Place the light on one side of the table just above and shining towards the object parallel with the surface of the table. Use a lens hood to prevent light striking the lens element
6. Place the object on the cloth, on the light side place a book or other thick object under the black material to prevent any light striking the object directly
7. Position the object under the lens and compose the image in the camera
8. The glass should then be placed on the opposite side of the set up to the light and the top should be rotated towards the light so that it is at 45 degrees to the table. It may be possible to use a special bracket or stand to support the glass
9. The light is then directed at the glass. Most of the light shines straight through the glass but some is reflected down onto the object, the illumination is even with reduced glare or deep shadows. Black card or material can be positioned on the side opposite the light to absorb stray light which has passed through the glass
10. Focus the image and take the picture

Axial lighting set up. Note the angle of the glass and how it is reflecting light down onto the coins

While there may be small marks and dust on the glass the camera should be focussing well beyond the glass surface and so imperfections will not appear in the final picture.

Can we convert our scanned documents into readable text?

Retyping printed documents is a very time consuming and therefore expensive process however, with the right software and a good quality original it should be quite possible to create editable digital text.

A scanner only records the tone or colour of the object it is scanning, it doesn't recognise the type of subject e.g. photograph, drawing or typed document. A printed word on white paper is digitised as a series of black pixels next to white pixels. However, some applications are able to identify familiar character shapes in scanned type and convert them into editable text. This is known as optical character recognition (OCR). Generally speaking, the higher the quality of the original material the more accurate the recognition.

While OCR software can deliver reasonably accurate conversion it will struggle at times. Ideally the original material should be in good condition, it should be carefully positioned in the scanner, the printed text should use a clean, easy to read typeface. Special characters or numeric characters such as ‘5' may go unread or be confused with letters.

It is rare for OCR software to deliver a 100% accurate conversion; there are usually some errors or suspect terms which need to be 'cleaned up'. The unedited product of an OCR program is normally referred to as 'dirty' or raw OCR. It is only when it has been proofread and suspect words corrected that it becomes 'clean' OCR.

The OCR application may allow the user to make some alterations to the scanned image to improve the success rate. For example correcting for 'keystoning', straightening the image, or increasing the contrast may all increase the accuracy of recognition.

Screen shot of OCR application. Frame on the left is the original image. The frame on the right shows the recognised type along with green highlighted errors. Screenshot courtesy of ABBYY Software.

You will need

• An OCR application
• Digital camera or flat bed scanner

How to do it

1. If you are using a scanner ensure the glass is clean (any marks may be confused with the text), if using a camera ensure original is as flat as possible
2. Place the artwork in the scanner and align it to the edge. If photographing it ensure it is evenly lit and frame the edges
3. Scan or photograph the object (it may be possible to scan from within the OCR application)
4. Open the OCR application (unless used to scan from) and open the scanned image
5. The application may attempt to read the document automatically or you may have to identify the areas of type and then start the process
6. The software should show you the original and the analysed text to compare side by side
   
   Left, original scanned document with analyse box around text. Right, ouput text with highlighted 'suspects'.
7. This can then be saved in an appropriate file format e.g. pdf or exported to another application such as Word
8. The text should be checked for suspect words and typos and resaved as clean OCR

Can our collection of glass plate negatives be digitised?

Glass plate negatives are old and very fragile objects and should be handled with extreme care.

While the optical quality of early cameras and lenses is primitive by today's standards, high quality glass plates are still able to resolve a large amount of detail and tone. A good negative may have a Dynamic Range (range of tones from black to white) which is beyond the capture range of many cameras or scanners.

Digital images made from glass plate negatives should never be considered a replacement for the original object which should be stored and possibly re-digitised again in the future as technology improves.

Glass plates can be scanned with care in a flatbed scanner that is capable of scanning large transparencies or negatives. The glass of the negative or the scanner can be scratched very easily. Glass plates are often broken as they are lowered or dropped onto the scanner glass or when the lid of the scanner is closed over them.

You will need

• A flatbed scanner, which can scan an area the size of your plates
• Clean cotton gloves
• Paper or thin card to support glass plate
• Foam rubber pads, card strips etc to take the weight of the lid off the glass plate

How to do it

1. Cotton or latex gloves should be worn when handling glass plate negatives
   
2. Check the condition of the negative, if necessary consult a conservator. It may be possible to scan a broken plate by carefully re-assembling on the glass
3. To avoid dropping the glass plate onto the scanner it can be placed on a larger sheet of paper, emulsion side down which is then lowered onto the scanner. The paper is then carefully withdrawn and the negative is lowered gently onto the scanner. Two shiny transparent surfaces in contact can create an interference pattern known as Newton's rings, this can be reduced or eliminated if the scanner is fitted with special Anti-Newton glass or by placing the non shiny (emulsion) side of the negative down. The final scan however may require flipping to correct left/right inversion
   
4. Thin cardboard strips can be placed around the edge of the scanner to support the lid and reduce pressure on the negative
5. Open the scanner software, check that the scanner is set to transparency, choose the highest available bit depth to capture as much tonal information as possible. Click Preview
6. Drag a crop around the negative, if you think you can improve the tonal quality of the image using the scanner software then do so
7. Click Scan
8. Carefully lift the plate from the scanner and return to storage

Scan made from glass plate negative

Can we scan our slide library?

Technically speaking, yes - providing you have the suitable hardware and software (see below). However, legally speaking a slide collection can only be digitised by the copyright holder. New licences are currently being negotiated in the UK, which may allow digitisation of analogue slide libraries under strict conditions but at the time of writing no agreement has been reached.

Colour transparency film - in a range of sizes from 35mm up to 10" x 8" - was the main format used by commercial picture libraries. However, with dramatic improvements in digital capture and the improved compatibility with modern workflows these collections have now been largely transferred to digital format.

With the increasing use of digital delivery methods in education, there is an increasing demand to digitise departmental slide collections. Dedicated transparency or slide scanners offer the very highest quality capture however these devices are quite expensive and can be quite slow. Some 35mm transparency scanners can be fitted with bulk feeders which can free the operator up to undertake other tasks.

Most flatbed scanners are capable of digitising filmstrips and mounted slides; some devices have frames onto which a number of slides can be placed. The average flatbed scanner is capable of providing sufficient quality for most forms of online and screen delivery.

Slides in frame ready for scanning

You will need

• A flatbed scanner that can scan mounted slides
• An image optimisation application to crop, correct tone colour and perhaps sharpen scans (optional)

How to do it

1. Edit images to exclude duplicates and select best examples
2. Check slides are free from dust, a blower bulb may help. DO NOT ATTEMPT TO BLOW DUST OFF YOURSELF - Saliva in your breath may stick to the slide and mark it permanently
3. Place slides on scanner glass or in mounted slide frame and with emulsion side up or down according to manufacturers instructions
4. Some scanner lids have a backing plate for scanning reflective objects; this has to be removed when scanning transparent objects
5. Ensure that the scanner is set to scan transparent positive originals
6. Make a preview scan and adjust capture settings to achieve optimum quality and resolution for needs
7. Crop the slides
8. It should be possible to select all of the slides and scan each one as part of a batch process
9. Save images

How do I capture large 2D objects that are too big for my scanner?

There are scanners capable of capturing 2D objects larger than A4 size but they are expensive and still have a maximum size limit. The most effective solution is to use a copystand. A copystand may be a dedicated  camera and artwork support or it might be improvised using whatever is available.

Left, camera mounted on copystand, separate lights positioned either side. Right, camera mounted on tripod with horizontal column

A copystand is basically a baseboard on which the artwork is placed and a column with a moveable head which holds the camera. Lights may be fitted to the sides of the stand or they may be on separate supports.

The camera can be raised or lowered on the column according to the size of the original. For small-scale projects a tripod with a horizontal bracket may be used and the artwork supported on a large flat surface such as a table.

You will need

• Digital camera and 'standard' focal length lens (35mm +)
• Copystand or tripod with horizontal arm
• Two or four lights of equal brightness and colour temperature (tungsten, fluorescent)
• Small spirit level (optional)
• Light meter or pencil to check even illumination

How to do it

1. Place artwork on the baseboard, non-fragile items which have an uneven surface may be held flat beneath a clean sheet of glass
2. Check the camera and baseboard are level, adjust if necessary
3. Make sure the lights are at equal distances from the baseboard and pointing down at about 45 degrees, check light isn't striking the lens
4. Use a lightmeter or a pencil (if the shadows are of equal density then the light is even) to check for even illumination. Adjust lights if necessary
5. Ensure that the camera's white balance setting matches the lights being used
   
   Pencil on copystand baseboard showing shadows
6. Adjust the height of the camera to frame the subject, avoid using lower focal lengths as this will introduce barrel distortion
   
   Setting a  longer focal length, this lens offers a wide 18mm setting, which introduces barrel distortion
7. Take the picture, the camera's self-timer may be used to reduce the risk of camera shake

As the camera is raised up the column it becomes harder to look through the viewfinder. Some cameras can be tethered to a computer, this allows the operator to take control of most of the cameras functions from desk level and reduces the risk of back pain, which is a common complaint from those using copystands for extended periods. We have a video presentation on setting up and using a copystand:

Video: Introduction to using a copystand

Photographing 3D objects?

Lighting is an essential element of all photographs however the quality of the light is very important when photographing 3D objects.

Before you start you need to consider a few things:

• Do you want natural atmospheric lighting?
• How big is the subject?
• Do you want to conceal or reveal surface detail?
• What lights are available?

Most digital cameras are fitted with built in flashes, these can be useful when no other light is available but can give a picture the 'rabbit in headlights' look.

Photograph taken with built in flash. Object has harsh shadows.

You may want to, or have to use available lighting. Available light is atmospheric though it isn't always easy to control; it is essential that you identify the colour temperature of the available lights before starting.

If you are using daylight you may need to choose a time when the light is most pleasing - low available light levels will probably require that the camera is mounted on a support to avoid camera shake.

Small objects (football size and smaller) can be illuminated with care using commonly available lights such as desk lights, larger objects may require flash or other specialist photographic lighting.

If you want to pick out the surface detail of the subject you may have to use a 'bare' light source and direct it along the surface of the subject.

If you want to reduce the shadows and surface texture you may have to point the light at a large white surface or direct it through a diffusing material. There is more information on lighting in our detailed documents.

You will need

• A light source. This could be sunlight, a desk lamp, or specialist photographic lighting
• A reflector such as small piece of white card (optional)
• Tripod or support (optional under bright light, essential under darker conditions)

How to do it

1. Place camera on tripod or support
2. Position light to achieve the most pleasing lighting. This isn't possible with daylight so you may need to move the subject or wait until the light changes
3. You may wish to use a reflector to 'bounce' some light back into the shadows
4. Set the appropriate white balance for the subject
5. Take the picture

Desklight from one side, white card reflector to bounce light into shadows

Image taken with desklight (camera right) and reflector (camera left)

Conclusion

This document introduces some simple methods of capturing a variety of different subjects. These approaches are not definitive and they can be adapted to suit different equipment set ups or subject types.

Last updated: 03 March 2010
Published in: Digitising analogue media | Creating new digital media |
Tags: analogue collections | bit depth | cameras | digitisation | equipment | hardware | optical character recognition | photography | scanning |

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