These guidelines have been prepared in response to a request from the Local History Association Computer Group for very basic advice on scanning photographs, negatives, slides and documents. There are many excellent web sites that offer advice on this subject but all too frequently the sites omit the detailed advice that a newcomer needs. To be told "ensure that you use an appropriate scanning resolution" is not very helpful when you are starting out and may be unclear what "an appropriate scanning resolution" might be. This article therefore includes some very specific suggestions about matters such as scanning resolution and image file format. However, it must be stressed that they are only given so that local historians wishing to make use of digital images in their projects can get started. It is very important to experiment with different parameters as more experience is gained.
The advice is given in the form of answers to the following questions:-
|1.||What can be done with digital images?|
|2.||What equipment will I need as well as my computer?|
|3.||Which image file formats should I use?|
|4.||Which storage media should I use?|
|5.||What software do I need to scan and edit images?|
|6.||What settings should I use when scanning?|
|7.||What changes can I make to my digital images?|
|8.||Which are the most useful web sites for help with scanning matters?|
1. What can be done with digital images? [top]
Digital images obtained using a flatbed scanner, or a dedicated 35 mm slide scanner or a digital camera can be put to a large number of uses. These include:-
2. What equipment will I need as well as my computer? [top]Note: The term samples per inch (s.p.i.) is a more correct term in some (but not all) instances for what is commonly referred to as dots per inch (d.p.i.).
It will be almost essential to have a CD writer so that you can store your images away from your computer (see Question 4). These are now less than £50 for a model which is fitted inside your computer. If you wish to add a CD writer to an existing computer system and you wish to avoid opening up the computer to fit an internal model it is possible to buy an external unit. These are usually connected via a Universal Serial Bus (or USB) connector which most modern computers have. An external CD-writer requires its own case and power supply and so tends to cost £30 to £50 more than similar internal devices. See Guidelines No 1 and No 2 in this series for general advice about computers and software.
3. Which image file formats should I use? [top]
There are literally dozens of image file formats but in order that as many people as possible can read your images it is important to stick to what has become the standard format for 'master copies' of image files - the TIF (or TIFF-Tagged Image File Format) format. There are a number of variants on TIF format and so it is best to store images without using any file compression. Although this results in larger file sizes compared to using compressed files it is safer for archive purposes as virtually all image editing programs (see Question 5) can read uncompressed TIF files. The format is a 'lossless' one and so unlike so-called 'lossy' formats no information is lost when the image is stored. Lossy formats such a JPG (developed by the ISO Joint Photographic Expert Group) are extremely useful for displaying images on web sites as they can be compressed into very small file sizes and can be readily obtained from the TIF master files.
The PNG (Portable Network Graphics) is a new standard for images used on the Internet but it has made little ground over the JPG format.
An excellent discussion on image file formats is available at www.rwsh.com.To Summarise: It is suggested that uncompressed TIF files are used for master images but JPG and other formats can be used to distribute and display versions of the images.
4. Which storage media should I use? [top]
Recordable Compact discs (CDs) represent a very good performance to cost ratio. Each CD can store about 650MB of data. Thus about 100 images produced in the GSIA slide scanning project referred to in Section 6 can be stored on a single CD. Andy Fadden's CD FAQ web site (http://www.cdrfaq.org) gives a vast amount of technical information about CDs.
The terms CD-ROM, CD-R and CD-RW are encountered frequently so what is the difference between them? In fact all three look physically very similar but they differ considerably in respect of how the information in stored. A CD-ROM refers to a CD produced by pressing a master disc against a blank CD similar to how a vinyl audio record is produced. A CD-R is written in a CD writer using a laser beam and once an area on the disc has been written that area cannot have its data overwritten. CD-RW refers to re-writable CDs which are also written using a laser beam but unlike the CD-R they can be erased and rewritten a large number of times. Nearly all modern CD writers are what is known as CD rewriters and can create both CD-R and CD-RW disks.
No one really knows the lifetime of CDs and estimates range from less than a year to 100 years! It makes great sense to ensure that multiple copies are made of important data and the CDs stored a separate locations. It is also a good idea to use good quality 'branded' CDs and to use two or more different manufacturers for the multiple copies.
A development of the CD is DVD which looks identical physically to a CD. Its capacity is up to 14 times that of a CD. The price of DVD writers has fallen significantly in the last year and they are likely to replace CDs in the relatively near future.
In comparison, a floppy disk can only store about 1.4MB (1.4 million bytes) of data and so their use is very limited for storing images.
5. What software do I need to scan and edit images? [top]
Nearly all scanners and digital cameras come with basic software to enable you to scan and load the images onto your computer and most of them provide software to edit the images (such as resize, alter the colour characteristics and crop). Excellent scanning software that works for many flatbed and film scanners has been produced by Ed Hamrick in the USA. This product is called Vuescan and is now used by the Author for most of his scanning projects. It costs $40 (about £30) and a demonstration version can be downloaded free of charge which produces a 'watermark' in the images until a license has been purchased.
Adobe Photoshop (Version CS) is still the industry standard for editing images but the full product costs more than £450 (inc.VAT). However, Adobe has released a cut-down version known as Adobe Photoshop Elements (Version 3) This has all the features most users require and is an excellent choice. It costs about £55 (inc.VAT)and is widely available. At about £80 (inc.VAT) Paint Shop Pro(Version 9) is a very popular and powerful program.
The Gimp (General Image Manipulation Program 2.0) is a very powerful freeware program which the developers claim is almost as powerful as the full Photoshop program. Xnview is a popular freeware image editing program that is worth considering.
The Irfanview image viewing software is freeware and is an extremely powerful and versatile program. It will rapidly create 'thumbnails' (small images) for all the images in a directory. Other features include batch processing where the same edit commands are automatically carried out for a number of files and the ability to create slide shows.
6. What settings should I use when scanning? [top]
Most scanning software allows you to control the scanning resolution (the number of samples of the image per inch captured in each direction) and the image mode. Not surprisingly your choice depends on the nature of the original and what use will be made of the digital version of the image. It is useful to start by considering when to use the three main image modes (monochrome, greyscale and colour) and the corresponding file sizes.
Some suggested 'starter' settings. Remember, it is very important to experiment with different parameters. If you wish to print enlargements of the original you will need to increase the minimum scanning resolution by the same ratio as you want for the size of the enlargement to the original.
Ideally you should record information concerning the caption, date, creator and the various settings within the 'header' of the image file. Only certain file formats allow this information, which is known as metadata to be stored in this way. Any further discussion of metadata is outside the scope of the present article but there is a lot about metadata on the Internet
7. What changes can I make to my digital images? [top]
It will depend on your software but most programs will enable you to:-
The ability to sharpen images is very important as the scanning process invariably 'flattens' the image, that is reduces its 'sharpness'. Appropriate use of a sharpness filter (e.g. the 'unsharp mask' filter) can make the division between different coloured areas in an image appear to be more pronounced and thus seem sharper. It is a very valuable tool that is often overlooked by beginners. However, if too much sharpening is used horrible effects will result. Where the degree of sharpening can be controlled sensible starting values of the three parameters that can be altered are amount = 150% radius=2 pixels and threshold=3. A threshold of 3 means that the colour values of adjacent pixels must be greater than 3 or the effect or sharpening will not be applied for this pair of pixels. The radius is the number of pixels surrounding the edge pixels that are affected by the sharpening and amount is how much the contrast of pixels is increased. This is where it is particularly important to experiment.
8. Which are the most useful web sites for help with scanning matters? [top]
There are many sites but the following are well worth a look:-
Waynes Fulton's Scanning Tips (www.scantips.com) A very good introduction
Tips for Scanning - Peter G Aitkin (www.pgacon.com/tips_on_scanning.htm)
Feedback on these notes will be welcomed. Please send them to the Author at email@example.com.[top] Ray Wilson January 2005