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Digital Image Capture and File Storage Guidelines for Best Practice Summary

Digital Image Capture and File Storage Guidelines for Best Practice Summary

Digital Capture and File Storage Guidelines for Best Practice Summary

The silver-based emulsion and chemical process used successfully for many years for the capture and storage of has now largely been superseded by the introduction of digital technology. The widespread use of digital among imaging professionals, archaeologists and the general public has created a vast array of digital information. If this information is to be of use now and for future generations, it requires the application of a systematic approach to how it is captured and stored.

Digital technology is still in its infancy compared with the long-established technique of using silver-based emulsions on glass plate or film to produce images that have, with suitable development and storage, proven to be stable and enduring. Some would argue that our records should still be made in this way, but film is becoming more difficult to source. In addition, film-processing laboratories are disappearing from our high streets, making local processing a thing of the past in all but the largest cities. The tide has turned in favour of capture, which offers many benefits that offset its unproven longevity. However, part of the problem with the digital environment is that its boundaries and possibilities are constantly changing. This publication offers guidance on digital image capture and storage to assist those involved with the making and keeping of images of the historic environment. It does not provide definitive answers regarding the problems of taking and storing digital images but does provide an overview of current recommendations.

This guidance note has been prepared by Steve Cole and Paul Backhouse

This edition published by Historic England July 2015. All images © Historic England unless otherwise stated. www.HistoricEngland.org.uk/advice/technical-advice/ Contents

1 The Digital Image Capture Process...... 1

1.1 Cameras ...... 2 1.2 Lenses ...... 3

2 Image Capture Standards ...... 6

2.1 File type ...... 6 2.2 Colour space ...... 8 2.3 Digital file and storage standards ...... 9 2.4 Storing digital image files ...... 11

3 Where to Get Advice...... 13 1 The Digital Image Capture Process

To enable the capture of an image, millions of (short for picture element) are gathered together into an array to form an . Image sensors can be the widely used charge-coupled device (CCD), the also widely used complementary metal oxide (CMOS) sensor, or the less widely used Foveon sensor, which is a derivative of the CMOS sensor. Pixels embed information about the scene projected onto the image sensor. Individual pixels only record how much light reaches them and not the characteristics of the light, for example its colour. In order to record colour information, each needs to be shown one colour of light through a filter. Three different coloured filters are used to record and reconstruct the image: red, green and blue. These primary colours of light can be mixed in different quantities to form any other colour of light. An array with a pattern of red, green and blue (RGB) filters is therefore placed in front of the image sensor to achieve colour information.

Each pixel needs to record information about the The quality of the image produced by any sensor light that reaches it through the filter. That light is determined by the characteristics of the light will be one colour but the pixel needs to record present at the time of , the settings of the how much of that colour there is (its saturation) , how the image is processed and treated and how bright or dark it is (its luminance). The during capture and post-capture, the quality of image sensor needs to record where the light the , and the skill of the photographer came from by knowing the position of the pixel in using the equipment. Larger image sensors with that recorded it. The light from each of the red, greater pixel counts will provide more information green and blue-filtered pixels is interpreted and but, for the reasons just given, it is not quite as processed to form the colour image (Foveon simple as more pixels means more information sensors work differently). and therefore a better image is produced, although more pixels will often lead to better tonal (the display of different levels of brightness contained within the image) graduation and detail in the image.

< < Contents 11 1.1 Cameras Aperture While it is possible to give a minimum resolution is the size of the opening in the in for the capture of digital images based on the the diaphragm placed in front of the sensor sensor size in megapixels, it should not be to control how much light is transmitted regarded as a definitive measure of image quality, through to the sensor. It is expressed as a as so much depends on other factors. However, ratio of the of the lens in terms assuming a sensor size of not less than 10 of f numbers or fstops. The higher value megapixels (and preferably larger), it is possible to f numbers ( F: 8, F: 11, F:16) are smaller define the type of camera that is likely to give the openings and pass less light through to the most appropriate image quality by understanding sensor. Lower value f numbers (F:2, F:4, the following technical characteristics. F:5.6) are wider openings and pass more light through to the sensor. Digital Single Lens Reflex (DSLR) camera These cameras usually offer the best optics and versatility. They generally provide the user with a Shutter speed is a measurement of the good interface and control over the image capture amount of time that light is shown to the process, and the engineering provides a rapid sensor expressed in seconds or fractions response once the shutter release is activated. of a second. Exposure is based on the The range of interchangeable lenses available combination of both aperture and shutter from the camera manufacturers and third-party speed, how much light is shown to the producers offers great potential for good results. sensor (controlled by aperture) and how long it is shown to the sensor (controlled by Compact shutter speed). Compact cameras can offer high-quality image capture but lack the versatility of DSLRs. Their small form makes them convenient to carry Other capture devices and easy to use. More recent models of both compact and DSLR cameras have the ability to At this point in time a suitable image is unlikely embed global positioning system (GPS) data and to be produced using a mobile phone or a camera applications to simplify making panoramic and within a pad or tablet computer. The cameras moving images. The complete automation of within these devices may have the pixel count to image capture can be an additional attraction of record sufficient information but do not offer the compact cameras but this should be approached essential refinements that are used to control with caution. It is important to be able to turn off other elements of image capture, such as the the full automation of any camera so that you can choice of focal length of the lens, the aperture and control it to suit the characteristics of the image you want to capture. ISO Rugged compact designs are available that The sensitivity of a sensor, how much protect the camera to some degree against it reacts to light, can be increased or the elements and accidents. Many compact decreased electronically by adjustment. and ruggedised digital cameras are used on The sensitivity of the sensor is expressed archaeological sites. by the use of a standard numerical setting issued by the International Standards Organisation (ISO). Low numbers 50, 100, 200 etc. are considered low sensitivities. High numbers 1000, 1600, 2500 and up are considered high sensitivity settings.

1 < < Contents 2 shutter speed and the ability to synchronise with 1.2 Lenses off-camera lighting, including electronic . The images produced by these devices have a very Wide-angle lenses noticeable that is caused by the small Architectural photography, unless a detail lenses used. In addition, the image produced by of something larger, is about capturing and a pad/tablet or mobile phone camera is designed conveying to the viewer information about large to be viewed on similar devices at a resolution things, ie elevations or interiors of buildings. A suitable for viewing on a screen (currently at wide-angle lens can be used to take a view of a 72 pixels per inch) and lacks the flexibility and whole building elevation, most of a room or a resolution for printed reproduction (which should large area of an archaeological site. be 240–1,200 dots per inch) at anything but the smallest size. Camera lenses, particularly wide-angle lenses, have characteristics that produce a distorted Other considerations image, most notably in the bending of elements The image sensor should not produce intrusive of a view that should be straight. These elements noise in the processed image. Noise is unwanted then appear to be bending outwards (barrel interference and degrading of the image caused by a distortion) or bending inwards (pin cushion number of factors during the processing of the image distortion) (Figure 1). Using the correct computer at the time of capture. One of the main causes of program post-capture enables the removal or noise arises when the images are taken in low levels reduction of this unwanted distortion. of light or when the sensitivity of the image sensor is increased [by increasing the International Standards Special wide-angle lenses called perspective Organisation (ISO) setting] to obtain images in low control lenses can be useful. These lenses levels of light. Using lower ISO sensitivity settings are used mainly in architectural photography and turning off any automatic facility on the camera to correct the distortion of perspective. This to increase the sensitivity at low light levels helps distortion becomes apparent when a camera reduce this problem. is used in a plane that is not parallel to the walls of a building, usually when a camera Image sensors should be free of dust and dirt is tilted backwards in order to capture the because such contaminants will be visible on the uppermost parts of the building. This changes the processed image. representation of the relationship or proportion of the parts of a building, making parallel The camera should be exchangeable image file lines appear to converge. The distortion of the format (EXIF) compliant so that appropriate perspective within an image makes a building about how and when the image was appear as if it is leaning backwards or falling captured will be embedded in the image. EXIF over. A perspective control lens eliminates this data records what type of camera is used, what distortion; some cameras have a perspective the camera settings are when the image is taken, control adaptor that can be used with more what colour space is used and how large the file than one lens. The perspective control lens, also is, so that the image can be described accurately known as a shift lens, has mechanical movements to the computer program that will open it. Most that allow the camera to be set in a plane modern cameras will be EXIF compliant. For parallel to a building’s vertical axis; mechanical time and date information to be accurate, this adjustments on the lens casing enable capture of information has to be input when the camera the uppermost elements of a large object without is initially set up and re-entered should such the need to tilt the camera. This advantage is only information be lost for any reason. GPS data gained if the camera is set up accurately so that it may also be stored in the EXIF data if the image is vertical to the plane being focussed on usually capture device is able to include it during achieved by mounting the camera on a and exposure or if it is added subsequently. adjusting it to be level using a spirit level.

< < Contents 3 Figure 1 Examples of barrel distortion (left) and pin distortion (right)

Telephoto or long lenses quality of a is always inferior to a A is any lens with a focal length fixed focal length lens. Modern zoom lenses do greater than the standard lens for the size of the offer very acceptable quality, and the convenience image sensor. The focal length of the standard of being able to vary the focal length probably lens is based on the measurement across the outweighs the loss of quality. However, be diagonal of the sensor, typically between 50mm wary of zoom lenses that offer a great range of and 55mm on an FX-sized sensor. (Using these focal lengths, as these are less likely to provide focal length lenses on the smaller DX sensor acceptable image quality throughout the range, typically magnifies the focal length ×1.5, making even using modern computer programs them telephoto.) The effect of this greater focal post-capture. length is to magnify the image and to narrow the . Telephoto or long lenses are useful for capturing distant or small subjects that cannot be approached. Sensor Sensor sizes are often defined in ratio to Zoom lenses the size of a 35mm film frame. DX sensors It is often possible to combine wide-angle are smaller (by various amounts) than a and telephoto lenses into one by using a lens 35mm frame and FX sensors about the same of variable focal length, ie a zoom lens. Any size as a 35mm frame. photographic textbook will tell you that the

3 < < Contents 4 Specialist lenses In general, the use of good-quality lenses that Photography at archaeological sites, or more are able to produce a sharp image across the specifically of artefacts found during excavation image plane is essential. Do not use the digital that can range in size from very large to very zoom facility on a camera. Unlike a zoom lens, small, may require the use of a macro lens or which actually magnifies the image using a lens with the ability to focus very close to an optical mechanics, a digital zoom crops into the object, to render the object at a suitable size and captured image to give the illusion of zooming quality on the image sensor. but the resultant file is a portion of the standard is defined as the reproduction of an object at its file the camera produces, leading to a reduction actual size or larger. This may not be necessary in image quality. in many cases but the ability to focus near to an object may be advantageous.

< < Contents 5 2 Image Capture Standards

2.1 File type bit depth to 24 comes at the price of a greatly increased file size. Additionally, not everybody There are many different kinds of digital image can open a 16- or 24-bit file, so for accessibility file. Generically, they are called raster images an 8-bit file has become the standard archive size. because they are composed of a matrix of pixels. You should check with your intended archive Most cameras produce a joint photographic for any specific requirements before submitting experts group (JPEG), raw (RAW) or tagged image any files. file format (TIFF) image file. Many cameras will produce a JPEG and RAW file at the same time. JPEG JPEG and TIFF are both open formats, which The JPEG file is a format that compresses the allows them to be opened and viewed by all image by discarding some bits of information, computer operating systems through many hence it is described as lossy, and grouping pixels types of imaging programs. Both also allow the together, to produce a smaller file. This is suitable embedding of EXIF and International Press and when storage space is restricted or if the image Television Council (IPTC) metadata (see below). is to be transmitted or viewed via electronic media such as the or attached to an TIFF email. It is an excellent format for accessibility The TIFF (version 6) is widely used and accepted and, in spite of the loss of information caused by as the standard file for archival purposes. A TIFF its compression, it provides a useful format for is described as lossless, ie it is uncompressed viewing, storing and exchanging images. and stores all the information captured, hence its relatively large size in comparison with the other It is important that JPEG images are not over- widely used open format, the JPEG (see below). compressed to make very small file sizes, as this TIFFs can be stored in 2-bit, 8-bit, 16-bit or 24-bit degrades the quality of the image. It is equally depth for each red, green and blue channel. The important not to repeatedly compress JPEG bit depth is the amount of colour information held images because more information is lost with within each pixel used to describe the colour of each compression, resulting in a lower quality the light it has captured or is reproducing. One-bit image. Merely opening and closing a JPEG image images would only provide enough information to will not alter its quality in any way, it is only produce a black-and-white image. A 24-bit image opening the image and saving it as a new JPEG will provide vast amounts of colour information file that will have the effect of further compressing about the subject, greater than the eye can it and degrading the quality of the image. perceive; even 8 bits per channel exceeds what the eye can see. The additional bit rates over and JPEG files are currently offered in two formats, above 8 bits allows for greater tonal graduation JPEG and JPEG2000. The former is widely used and depth of colour. However, increasing the by most camera manufacturers and imaging

5 < < Contents 6 programs. The latter, which was developed in the images because improvements in computer year 2000 as an intended replacement for JPEG, programs will enable more and better information has not been widely adopted in spite of it offering to be extracted from them in the future. This view many advantages in terms of compression and is not universal, however, because, unlike TIFFs metadata storage. Few, if any, cameras capture and , RAW files are not an open format: they JPEG2000 files, and support among web browsers can only be opened by camera-specific programs is limited. The use of this format as a storage or by expensive imaging programs such as Adobe medium is more common but at this time it is not Photoshop, which will open most current RAW files recommended because of its limited support. but not all. Additionally, the camera manufacturers that own the RAW file format can change the way RAW they write their RAW files over time, sometimes The other file format that demands attention is removing earlier RAW formats. It may not be RAW. RAW files are widely used by photographers possible to open a RAW file from 10 years ago in because of the flexibility offered by this format current RAW converter programs. This restriction is post-capture. A RAW file provides the data as why TIFF is the file of choice for an archive. captured by the camera, ‘what the pixel saw’, with minimal processing applied. This means Adobe has tried to standardise RAW file data the pixel data can be uploaded into a computer by using a universal open file format known as program for interpretation and processing. The (DNG). This file format contains RAW data can be manipulated in many ways to all the data necessary (lossless) for interpretation adjust colour, exposure and saturation, and even and conversion to other file types such as TIFF or bring back detail not readily visible in shadow JPEG. Adobe also offers a free RAW file converter and highlight areas of an image. In addition, that will convert camera manufacturers’ RAW corrections can be made to compensate for file formats to the DNG format for interpretation defects in image quality brought about by via various computer programs. Unlike the TIFF, imperfections in the lens. Many lenses for current however, take up of DNG has not been universal. and future cameras are/will be designed to make use of the capabilities of a computer program to All RAW files require additional processing in a correct distortions in the image produced during computer program to get the best results and image capture. Like JPEGs and TIFFs, RAW files make the images accessible to others, which can allow the embedding of EXIF and IPTC metadata. be time consuming. If photography is not your primary occupation, taking images as JPEGs The use of RAW images as archive files is an area and saving them as TIFFs is a time-saving image of debate. Many believe that storing RAW data production work-flow. However, some loss of files is the best and most useful way to archive quality will result from this practice.

< < Contents 7 2.2 Colour space White colour balance Most digital cameras will give a good colour As the name suggests, colour space is the space in rendition for a wide variety of lighting conditions which computers and cameras store the information when the white balance setting is set to auto. that describes the colour of an image. There are Using this setting in mixed light sources will often three main choices of colour space that are widely produce the most neutral results. However, there used: Adobe RGB 1998, sRGB and CMYK. The size of are times when setting the white balance within these spaces and therefore the colour information a camera to a colour temperature setting will that can be contained within them vary. produce a more accurate and more consistent colour rendition. Adobe RGB 1998 This is a large space with the capability of Colour Temperature describing millions of colours (wide gamut, range Light comes in different colours which is or spectrum). It is an additive colour system classified by using a system developed that is based on the different amounts of red, by William Thomson Kelvin—colour green and blue (RGB) light that need to be mixed temperature and is expressed in degrees together to produce any colour. Digital cameras Kelvin. The light that we see ranges in and computer screens are RGB devices. colour temperature from about 1700 degrees Kelvin (candle light) up to 27000 degrees sRGB Kelvin (as reflected from a blue sky). This is a smaller colour space that also describes millions of colours, although fewer than Adobe Digital cameras have the ability to be set RGB 1998. This smaller gamut is primarily for different colour temperatures of light designed for colour monitors, domestic colour and this is done using the white balance printers and the Internet, hence widely used. As settings. As the name suggests this is a with Adobe RGB, it is an additive colour system. setting to reproduce white objects white/ Many cameras will only offer the sRGB colour neutral when they illuminated by light space for image capture. sources of different colour temperatures.

CMYK CYMK differs from RGB colour spaces because Using any of the standard, daylight, cloudy, it is based on a subtractive colour system for tungsten, etc., settings will keep the same colour colour-printing inks. Printed colour images are temperature during a series of images. This will made up from cyan (C), magenta (M), yellow (Y) provide consistency in colour reproduction as and black (K) (CYMK) inks. The CMYK colour space long as the light falling on the subject does not is the smallest of the three and is designed to change substantially during the exposure period. accommodate the colours that can be reproduced on a printed page. Tungsten/Incandescent As both sRGB and CMYK limit the number of The camera is expecting to receive light colours that can be described, it is desirable to of a colour temperature of between 3200 capture images in the Adobe RGB 1998 colour degrees Kelvin and 3400 degrees Kelvin space if it is available on your camera. If required, which is the colour temperature that conversion to either of the other colour spaces photographic tungsten light bulbs are set can be carried out post-capture. to operate at. Domestic incandescent light bulbs usually run at a colour temperature of less than 3200 degrees Kelvin and consequently produce images on this white balance setting with a warm (red) cast.

7 < < Contents 8 Using the fluorescent and tungsten settings also Dynamic range helps achieve colour accuracy in the captured Exposure should aim to produce good highlight image. Fluorescent lights in particular have a and shadow detail. This can be difficult at many green bias that is unseen by the eye but captured buildings and archaeological sites because the by the image sensor. Fluorescent light has an levels of light in the highlight and shadow areas extra amount of green light (peak) which the of a scene can be brighter or darker than the eye and brain ignores but the cell will see and sensor can record. The eye is able to adapt to reproduce images with a green cast. Using this take in these extremes but the sensor disregards white balance setting will activate program to excess brightness, making everything beyond its remove this extra green light from your image. sensitivity white. At the other end of its sensitivity range, the sensor fails to register any detail in the darkest areas, making everything black. Known as 2.3 Digital file and storage standards the dynamic range, these extremes of luminance level can be reduced and brought within the range File type that the sensor can capture with the introduction Archive image files should be uncompressed 8-bit of additional lighting (most practically an per channel TIFF version 6 files of not less than 25 electronic flash or sometimes a large ) to megabytes (without interpolation). The files should illuminate the shadow areas. Highlight luminance be flattened (ie not contain image adjustment or levels can be reduced by reducing the level of other working layers introduced post-capture by light falling on the subject using a diffuser. Large some image-editing computer programs). and very dark or bright areas that are impractical to light can be tackled using the technique known Sharpening as high dynamic range (HDR) photography. The Archive Images should not be sharpened. basics of this are that the camera is placed on Image sharpening is offered by many image a tripod or other stable platform and several manipulation programs. This works by increasing exposures of the scene are made using a range the contrast at the junction of each pixel giving of shutter speeds to increase or decrease the the impression of sharper edges between them exposure delivered to the image sensor. Changing and greater overall contrast. For scanned images the shutter speed is better than altering the as opposed to camera images it is usually aperture because of the effect this will have on necessary to apply a degree of sharpening as the in the image. This series of some sharpness is lost during the scanning exposures should be calculated to produce detail process. Sharpening is also applied at the taking at both ends of the range of luminance within the stage of images produced in camera as part of the scene. This series of identically composed but capture process. Care should be exercised on the differently exposed images can then be imported application of any additional image sharpening. into a computer program to combine them, In general, sharpening should not be applied to thereby including information from a very wide any archive image as sharpening is dependent on range of luminance captured in both the highlight the size that the image is going to be reproduced. and shadow areas. However, the use of extreme The future reproduction size of any archive image HDR techniques can lead to very unusual looking cannot be known. images; these may be eye catching but are not truthful reproductions of the subject matter. Output sharpening can, if necessary, be applied to a copy of the original when preparing the image for reproduction once the size of reproduction is determined.

< < Contents 9 Artefacts Description: what it is; where it is (county, district, Files should be cleaned of all sensor dust marks parish); who it is; why it was taken. visible at 100% view, ie visible on screen. Author: the photographer’s name. Metadata The metadata included with a file should contain Copyright: who owns the image and where information under the following field headings. to apply for permission to use it if copyright restrictions are to be applied. EXIF This provides the camera data and date and time GPS: where possible, this information should be information. included at the time of image capture or added post-capture. If captured by the camera, it is XMP and IPTC metadata worth remembering that the GPS records the Extensible metadata platform (XMP) is the position of the camera not the position of the technology originally created by Adobe and image subject. This is significant if a building is later adopted as an ISO standard for the distant from the viewpoint. creation, processing and interchange of standard and customised information for Keywords: the addition of keywords will assist images and other digital resources. The XMP file searches for the subject matter. Provide a list of contains information set out in a standardised at least three keywords that describe the subject format devised by the International Press and matter captured within the image. Thesauri Telecommunications Council (IPTC) within which of controlled vocabularies are available from additional information as well as the EXIF data Historic England (see table below). can be added to the metadata file embedded in the image. The minimum additional data Origin: the ‘Transmission Reference’ box should that should be added comes under the contain the job or order number if there is one. following headings:

If your project: Use this Historic Available from this web address: England (HE) thesaurus: includes specific monument Monument types http://thesaurus.historicengland.org.uk/thesaurus. types asp?thes_no=1&thes_name=FISH%20Thesaurus%20 of%20Monument%20Types includes specific types of Evidence http://thesaurus.historicengland.org.uk/thesaurus. evidence asp?thes_no=92&thes_name=FISH%20Evidence%20 Thesaurus2 recovered marine evidence Maritime craft types http://thesaurus.historicengland.org.uk/thesaurus. asp?thes_no=143&thes_name=FISH%20Maritime%20 Craft%20Types%20Thesaurus includes a particular event Event types http://thesaurus.historicengland.org.uk/thesaurus. or process asp?thes_no=566&thes_name=FISH%20Event%20 Types%20Thesaurus

Thesauri of controlled vocabularies available from Historic England.

9 < < Contents 10 The ‘Instructions’ box should contain additional for example Adobe Lightroom and Capture One information about the image, in particular any from Phase One; these save time and alleviate the restrictions on image use. need to copy the files manually.

General Backup can be simplified with the use of Images should be free of any technical programs purchased or downloaded free from the imperfections such as camera shake, and Internet that compare the drive being backed up over- or under-exposure. All architectural images with the drive or drives being backed up to, and should be vertically true (achieved at the point of only transfer the files that have changed. capture using perspective control or post-capture using computer programs) unless deliberately The downloaded files should be placed into untrue for dramatic or artistic purposes. folders named by site and date. Metadata as outlined above should be added to the files.

Lens Flare Naming files Lens flare can either be a reduction in the Digital cameras give a unique number to each contrast and saturation of an image due image taken but this can be reset by accident and to unwanted light (non image forming) there may also be a limit after which the numbers hitting the lens and causing a haze across will be reset to the first numbers used, thus the image or alternatively a manifestation risking duplication. It is good practice to apply of reflections from within lens mechanism non-camera-assigned numbers to images to avoid displaying as a bright line or several bright more than one image having the same number. circles at far and near points within the Files can be renamed at the time of download or image. These circles may sometimes reveal after post-capture work when the finished archive themselves as polygonal reflecting the shape file is created. of the iris (aperture) within the lens barrel. There are many conventions for naming files. They can be named purely by number, for example 0000567, or they can be named by site and 2.4 Storing digital image files number, for example The Grange Netherhampton 0024, or perhaps with something signifying As soon as possible after capturing digital images the photographer’s name, for example Jones it is advisable to download the files from the 000551. The important thing is that each image camera memory card onto two or more computer should have a unique identifier so that it can be hard drives. Using a card reader for this is safer referenced and found again when needed. than connecting the camera directly to the computer, as a direct connection to the camera Storage of the finished and uniquely numbered requires dual functionality of the camera to read files should occur on several drives and in different and transfer the files at the same time. Hard disk locations until they are deposited in an archive. drives are susceptible to failure and valuable data should be stored on more than one drive The cloud: off-site data storage and preferably in more than one location in case A secure, effective and expandable method of of some disaster occurring in the location where storing your image files, or any file, is to use the the data are normally kept. The storage drives services of a cloud storage company. The cloud themselves need to be regularly backed up so is a generic term for data storage on servers that any changes made to files on one drive are that can be accessed from a computer or other reflected on the other drives. Losing a day or a web-enabled device from anywhere in the world week of post-capture work is worth avoiding. provided there is an Internet connection. There There are some computer programs that offer the are many different companies to choose from, facility to download and backup at the same time, some allowing limited storage for free and others

< < Contents 11 charging for the amount of storage space used. data to another party who may lose it or deny Many offer other refinements, such as computer you access to it should a dispute arise. There are programs to back up your files regularly or also potential copyright issues with some cloud encryption to make sure your files are secure. service providers, and it is worth noting that Cloud storage can also mean you can share currently government agencies and semi-public your data with selected parties via a secure link, administrative bodies are not permitted to use although the sharing of an archive file needs careful cloud storage or cloud processing that involves consideration because of the possibility of loss or servers outside the European Union (EU), which unwanted changes to the file. It is better to allow limits the services available. this kind of access to copies of files rather than originals. Other than running your own backup How and wherever your images are stored, servers, having securely stored files in the cloud is it is important that their accessibility is kept perhaps the best way of ensuring their survival. up to date by ensuring that the hardware, software and file types used for storage do The disadvantages of any cloud storage is that not become redundant. This can be achieved the transmission of large quantities of data to by transferring/transforming the data during the servers of the storage company can be time transition periods. Major changes to technology consuming if the connection to the Internet has or preferences for storing files are unlikely limited bandwidth, and it can be expensive if you to happen overnight; the means of updating have a limited data contract with your Internet usually exists during the transition period but service provider. In addition you are handing your becomes harder to source thereafter.

11 < < Contents 12 3 Where to Get Advice

For more information on the IPTC photo metadata For the use of the RAW file format in photography, standard, see http://www.iptc.org/cms/site/ see the following: index.html?channel=CH0099 Andrews, P 2007 The Complete Raw Workflow For more information on JPEG2000, see Guide: How to Get the Most from your RAW Images http://www.jpeg.org/jpeg2000/ in Adobe Camera Raw, Lightroom, Photoshop, and Elements. Focas Press , Abingdon, Oxfordshire For guidance on good practice regarding raster images, see the Archaeological Data Service (ADS) Evening, M 2007 Adobe Photoshop Series for http://guides.archaeologydataservice.ac.uk/ Photographers. Focal Press, g2gp/RasterImg_Toc http://www.focalpress.com

For further explanation regarding bit depth, Verhoeven, G J J 2010 ‘It’s all about the format: see http://photo.tutsplus.com/articles/post­ unleashing the power of RAW ’. processing-articles/bit-depth-explained-in­ International Journal of Remote Sensing 31(8), depth/ 2009–42,

For imaging essentials, see http://help.adobe. Wheatley, D 2011 ‘High dynamic range imaging com/en_US/photoshop/cs/using/WSfd1234e1c4 for archaeological recording’. Journal of b69f30ea53e41001031ab64-7949a.html Archaeological Method and Theory 18, 256–71, http://eprints.soton.ac.uk/162413/ More information on digital technologies in education and research (UK), see http://www.jisc.ac.uk

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