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Scanning

If you scan well, you're off to a good start with your graphics. You can always lose quality during the manipulation process, but you can't really increase it - so the idea is to get the best scan practically possible in the first place.

I've been told that you should always scan an image at Output-resolution, which is the resolution or dpi you will be using it at. If you were printing it out, that could be between 300 and 600 dpi (dots per inch). Screen resolution is much lower, either 72 or 96 dpi, depending on the monitor.

Unless you intend just using the image directly "as is" after you've taken the scan, I don't agree with scanning at Output-resolution, though. It doesn't leave you any room for resizing and other manipulation. I usually scan at around double my intended Output-resolution (my final graphics are all 72 dpi for web use).

Scanning at 144 dpi still means an image is small enough to be quick and easy to manipulte - this would be a different story working at print-resolution, but I'm just going to focus on web-use here.

I also scan at "high colour", "full colour" or "millions of colours" (the name depends on your scanning software, but you get the idea). That even applies to simple black and white pictures like the one at the right, even though it's final state here is only 16 colours.

I do all of the manipulation at the higher resolution and full colour, and then when I'm happy with it, I drop down the resolution and number of colours to optimise the filesize.

If your scanner software has automatic straightening or anything else, turn it off if you can. Always try to scan the image straight in the first place, or if it really needs "straightening", do that in a professional graphics package, you'll get a much better result than any nasty auto scanning software can give you. Pixels are square, and so any rotation that's not a multiple of 90 degrees will mean loss of quality.

Another thing that loses picture quality is increasing size digitally, since your software has to simply invent the image information in between the original pixels. The way around this is to consider your final intended size when you scan, and scan at a resolution that means you will be shrinking the image rather than enlarging it to get the size you want. For example, if you have a picture that measures only 2cm wide in a book, but you want it to be 4cm wide on your web-page, scan it at 144 dpi and then when you change the image properties to screen resolution of 72 dpi - oila! It's double the size. Never enlarge an image digitally, it will look horrible.