Scanning images
One way to source digital images is to create your own by scanning images from books, photographs or slides. As each scanner is slightly different in its operation, this section doesn't give a step by step guide to using a scanner, but tries to explain the basics of scanning by answering the following questions:
- Where can I use a scanner on campus?
- How do I use a scanner?
- What settings do I need to adjust?
- How do I know what resolution to scan an image at?
- What other scanner settings do I need to know about?
- Where can I find out more information?
Please remember to follow copyright guidelines if you are scanning an image that is not your own slide or photograph - look at Copyright and the use of images to find out more.
Where can I use a scanner on campus?
If you don't have access to your own scanner, the University has scanners that you can use to scan photographs or images from printed material which can be saved onto a memory stick to take away with you. Scanners are available at:
- Main Library, Whiteknights
- Palmer G05B, Whiteknights
- Library, Bulmershe Court
Your own department may also have scanning facilities that you can use.
Back to topHow do I use a scanner?
Laminated guides explaining how to use University scanners are available by each scanner, or you can read the 'Scanning Quick Guide' on the ITS web page: More Help - Scanning, Printing, Storing.
If you own your own scanner, you need to follow the instructions that came with it. However, the following information should help you to understand the different options.
Back to topWhat settings do I need to adjust?
The most important setting you will need to adjust is the scanning resolution. When scanning a document, resolution refers to how much information is captured by the scanner, measured in pixels per inch. For example, if the scanning resolution is set to 300 dpi, 300 pixels of information will be captured for each inch of the original document. If your document is a 6" x 4" photograph, the resulting image will be 1800 x 1200 pixels in size (6" x 300 ppi, etc). If you increase the scanning resolution, you will end up with more pixels in your scanned image (and a larger file size). A more detailed explanation about image size and image resolution is given in Understanding digital images.
Back to topHow do I know what resolution to scan an image at?
Often scanners have some pre-determined resolution settings that you can use depending on whether you are scanning for screen display or print (usually 150 dpi and 300 dpi respectively). This may be fine for when you want to reproduce an image at the same size but may not give you enough flexibility if you want to change the scale of your original image. If that is the case, you may need to use the advanced settings where you can choose your scanning resolution more precisely.
In order to choose your scanning resolution, you need to how you are going to use the image: will it be displayed on a screen or printed out, and what size do you need the final image to be? Then you can work out how many pixels you need to capture in the scanning process which will tell you the resolution at which you need to scan.
On the whole, it is better to end up with a larger image than you need as it is easier to reduce the image size later, but impossible to enlarge it without degrading the quality. However, there is no point in having an image that is much too large as this may cause problems in terms of computer performance or storage space. Similarly, if you put such a large image directly in a document, it will cause the document to load very slowly which may be problematic if you are giving a PowerPoint presentation.
Tip: in the Advanced Settings area of some scanners, you can set the output size in pixel dimensions rather than image resolution - this may be easier to work out than the scanning resolution.
Scanning for PowerPoint (or web display)
As discussed in Understanding digital images, if you are displaying an image on a computer screen, you need to have one pixel of image for each pixel on the screen. If you have a screen of 1024 x 768 pixels (the most common screen size), you would need an image with at least that number of pixels in order to fill the screen (or proportionately less if you only want to display your image on part of the screen).
To work out the scanning resolution, simply divide the number of required pixels by the length of the original image (in inches).
For example, if you were scanning a 6" x 4" photograph, you would need to perform this calculation to work out the required scanning resolution:
number of pixels needed (1024 pixels) ÷ length of original image (6")
= scanning resolution (170 dpi).
Scanning for print
It is slightly more complicated if you are scanning an image to put into a printed document. Printing requires at least 150 pixels per inch in order to get a good quality image, so this needs to be taken into account when calculating your scanning resolution. Therefore, you need to work out the size you want the printed image to be in inches, multiply this by the printing resolution (150 dpi) to find how many pixels you need in your scanned image, and then use the equation given above to find out the scanning resolution.
For example, if you were scanning a 6" x 4" photograph and you wanted to print it out at 3" x 2", you would need to perform this calculation:
size of image required (3") x printing resolution (150 dpi) = number of pixels needed (450)
then…
number of pixels needed (450) ÷ length of original image (6") = scanning resolution (75 dpi)
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What other scanner settings do I need to know about?
Some other common settings that you might need to know about include:
Bit depth (or colour settings)
Your scanner may offer you a choice of several colour settings, such as black and white, greyscale or colour. As discussed in File Sizes, this refers to the amount of colour or tonal information that is captured during the scanning process. For colour images, 24 bit colour is the best option (sometimes called 16 million colours, or true colour), allowing good representation of colour in the scan without the file size becoming too large. A higher colour setting is sometimes available but is only needed for specialist users who might be doing a lot of colour manipulation once the image has been scanned.
The greyscale setting should be used for black and white photographs where colour information is not needed, and the black and white setting may be useful for simple line drawings, such as charts, tables and diagrams.
Descreen
This is a setting that gets rid of the grid-like pattern (known as 'moiré') that sometimes appears in a scan taken from a printed book. This pattern is a result of the printing process and can make a scanned image look very unsightly. However, the descreen setting works by gently blurring the image to make the moiré pattern less noticeable, but for some images with fine detail this will not look acceptable either. One solution is to try scanning at a higher resolution than is required with the descreen setting turned off and then resizing the image.
Dust/scratch reduction (or Digital ICE)
This setting can be used to get rid of any scratches or dust particles that were present on the original when it was scanned. However, as with the descreen setting, this may result in a slight softening of the image, which may or may not be acceptable. To avoid having to use this setting, try to ensure that your original image is as clean as possible before scanning.
Back to topWhere can I find out more information?
There is a lot of general information on scanning images available on the web. Some sites to recommend are:
- JISC Digital Media's scanning guides
- Cornell University Library's digital imaging tutorial
- Scantips.com
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