You're simple request is more complicated than you think. The short answer
is that you can only expand an image up to a point and correct for the
blurriness. Beyond that no amount of sharpening will help. Without going
into a long tutorial, here are the quick facts.
1. Generally, images can be expanded up to 10 percent without a serious
compromise of quality. After that you are going to see some degradation in
image quality though it may not matter to you.
2. If your image is for print purposes, you require a minimum number of
ORIGINAL pixel information for acceptable prints at any given size. The
larger the picture the larger of pixels required. Most commercial printers
can give you guidance in this regard.
For example, for a standard 4 x 6 inch print, you should have 800 x 1200
pixels (1 meg) of information. For a good print, you need 1200 x 1800. (2
megs).
3. Scaling a smaller image up to a larger size won't give you a photo as
sharp as one that was taken at that larger size by a camera designed for it.
The software that enlarges the photo will produce a certain amount of error
that shows up as blurriness.
Irfanview will show you pixel info about the image you're viewing in its
status bar at the bottom. You can resize your image (Image | Resize /
Resample) then use the sharpen filter (Image | Sharpen) to try to improve it
somewhat subject to what I wrote above. To fine-tune the sharpening, go
Image | Effects | Effects browser and you can sharpen your image more or
less.
There are other tips and tricks that might be helpful, but for simple stuff
that's all you need to do. For more info:
www.scantips.com for lengthy discussions of scanning, resolution, etc.
M
)