What is resolution and what is best for my pictures?

People get very confused about resolution.

Resolution is often measured in dpi (dots per inch).

A computer monitor (and T.V. sets) don't use dpi at all. They work on the pixel size of the image (a pixel is essentially a little dot that is used to make up a picture).

Printers however do use dpi. The pixel dimensions mean nothing to a printer and instead they just lay down the dots based on the dpi. So the dpi will determine the overall size of an image.

It starts to get complicated when you try to increase the size of an image.

For a screen you have to add in extra dots that are not there in the image. This is done by very clever software (some more clever than others) and as long as you don't go too big you can hardly notice the difference.

For printing you tell the printer to use less dots per inch so the dots you do have go further. So the greater you increase the image the less dots are available and so the image quality will deteriorate. However most but the very smallest images cope with this very well. Again there is some clever software than can help with the problem.

There is a rule of thumb that says you can get photo quality printing at 200dpi (probably closer to 150dpi though). This means that a photo scanned at 600dpi could be easily printed at 3 (maybe even 4) times its beginning size without noticing any loss of quality. This is more than enough for most people.

All this adds up to not needing to worry too much about resolution and don't be overly impressed by those who offer to scan at much higher resolutions.

However there is something else to bear in mind and that is grain size.

Just as there are dots on a screen that make up the image so there are dots (or grain) in a photo.

Have you ever seen images from a powerful microscope that zoom in so you can see the fine detail of something? Well a similar thing happens to images when you scan them at too high a resolution and you start to see the grain in the paper or film that it was on.

So if you scan at too high a resolution your picture comes out worse than if you scan at a lower resolution because of the grain of the film or photo paper.

For a printed picture this means that anything over 600dpi is just too big and you most probably be picking up grain from the paper. The best approach if you need your picture bigger is to scan it at 600dpi and then enlarge it using software. This will not be a perfect enlargement but it will be better than scanning it (we would also recomment using a tiff format for this kind of scan - see more information here).

For a slide or negative things are a little different and the vast majority (save a few professional and very expensive films) should not be scanned in excess of 3200dpi. Often a much lower dpi is fine for most kinds of work.

Please don't get sucked in by those who try to impress with high resolution scanning, they either don't know what they are talking about or they are trying to fool you.

If in doubt ask and we will be glad to help you.