Here are a few tips for getting a good balance between quality and file size when scanning prints or slides for the web. These are based on my own experience, supplemented by advice from www.scantips.com , a place for excellent (but long winded) advice on scanning. These notes can only summarise a subject that can, and has, filled books.

Any photograph can be scanned successfully, no matter how old and faded. Image processing software can improve the quality of the most damaged photo, hiding tears, spots of mildew, increasing contrast and even sharpening the image.

There are many cheap scanners around, and they can all scan well enough for use on the web. Unless you plan to make high resolution scans, don't pay more than you need to. I get perfectly adequate results from prints with a £45 scanner. (Canoscan 3000F)

35mm slides require a specialised slide scanner. A reasonably priced one is available from Jessops, the .Primefilm 1800u, price about £70. However, this can only scan 1 slide at a time, and I have a lot of slides. I have recently upgraded to a Minolta Dimage Scan Dual IV, about £240, and this hoovering through 40 years of slides, and is definitely worth the extra money.

Resolution can be ignored! This may seem counter-intuitive, given that scanners advertise how high a resolution they can achieve. Resolution on the web is set by the user’s monitor. For example, if you have it set to display 640 x 480 pixels, resolution will be low and the image grainy, but the image will be big. Conversely, if you set your monitor to 1024 x 768 pixels, then resolution will be high, but the image small.

So, what counts is the number of pixels in the image. For web use I resize my images to 800 pixels across for landscape format, or 600 pixels high for portrait format. This will just fill the screen on 800x600 monitors, and three quarters of the screen on 1024 x 768 . Of course, the number of pixels in the image depends on the scanner resolution you set during the scanning process. Read on for details.

All scanners are different, so I can only offer general advice. The principles are identical, the means of achieving them may vary.

• Switch on the scanner, start the image processing software, or the scanner’s own software. (It is usually better to scan from within an image processing package, if you have one, but this is not essential.)
• Place material to be scanned face down on the scanner, squared off as much as possible.
• select "preview", to obtain a small low resolution image in scanner's software control panel.
• use the controls to crop the image, as required. Be sure to leave space around the main subject so the image can be adjusted later.
• set the resolution to 150 dots per inch (dpi). For a small image, set this to a higher resolution, say 250 or 400, to allow the image to be expanded. All other controls should be at their default setting.
• Select "scan" to (surprise!) scan the image.

Save to disc

• save it to disc as a "jpeg" file, with a ".jpg" extension, giving it a meaningful name so you can find it again. Jpeg compresses files, throwing away information as it does so. The more you compress, the more it throws away. However massive reductions in file size can be achieved without compromising quality. 
• I used to recommend saving the file in an uncompressed format (eg .tif or .png), but I have found through experience that saving as a .jpg with low compression saves a massive amount of disc space without sacrificing quality. Note, however, that if you continually work on a jpg, and keep saving it to the same file, quality drops and file sizes increase.

• email it me as an attachment. 

Because the image is very small, much higher resolution is required to obtain a reasonable size of image on the screen. Using the Jessops slide scanner; and trial and error; I find the following settings work well:

• resolution - 1000 dpi, multiplier - X1, quality - high, all other controls set to default.
• From this point, the scanning process is the same as for prints. A scan of the full slide will give a long side of about 1400 pixels, a good starting point for image processing, which can later be reduced to 800 for the web. It is always better to reduce the size, rather than to increase it.

Using the Minolta, I batch scan 4 slides at a time on the "2 Megapixel camera" setting, giving 1600*1200 pixel images.

4.3 Printing 

You will find that a resolution of 150 dpi is entirely adequate. Higher resolution cannot be seen by the eye, results in bigger file sizes, slower printing, and wasted ink. In my experience, it is difficult to better the value for money and quality you get from taking a CD or memory stick into Jessops. So an image that is 1500 pixels X 800 pixels will happily produce a 10"X8" print. (I.e. 150 dpi*10"=1500 pixels.)

This document is intended as a quick guide, to help anyone to produce an adequate scan. I have avoided a whole raft of complicating detail which a purist would reckon essential. If you have any queries, email me & I will try to assist (but no promises).

6   Photo Editing Software

If you are planning to scan and keep a number of pictures, or have taken up digital photography, then good image processing software is invaluable. I use Photoshop Elements, which I find entirely adequate, and is compatible with Photoshop itself, a heavyweight professional (and expensive) software suite.

Isaac Newton, www.hmssirius.info; www.hmsbacchante.co.uk, www.hmsminerva.info, www.pippins.me.uk

4th Jan 2006

Page updated 04-01-06