I see some of the images uploaded on the Forum, particualrly thos of documents, are too large for most PC monitors and make viewing difficult because we have to scroll all over the page to read the text - and it's easy to lose track of the meaning when so doing.
I suspect I am 'teaching' people to suck eggs here, but I find images sizing to be difficult. I find it confusing. These are my noddy notes:
Basically, an image has two sizes relevant to what we do ... the printed size and the on-screen size.
To get a decent print, scanners will typically be set at say 300 dpi ... your printer will squeeze in 300 dots to each inch of the paper its printing on, and will print out to the size of the page, e.g. A4. Thus you get a good quality print, the same size as the original, because you have all those dots in just one inch.
However, unlike your printer which can vary the number of dots it puts to each inch of the age it is printing on, dots on your PC monitor (your viewing page) are fixed at say 800 or 1024 dots across the screen and 600 or 768 dots in each vertical column going up screen.
A scan of 300 dots per inch (dpi) on a document 8 inches wide and 11 inches high results in 2,400 dots in width and 3,300 in height. If your monitor is set at 1024 x 7678 then you will have to use the scroll bars to see the whole document - this is why many documents we see on the web do not comfortably fit our PC screen.
This dpi size and the physical size of the original docuemnt can also result in a large file size and long download time. For example, an A4 page in colour can be over 4 Megabytes and for those on dial-up it will take a long time to download or 'appear'. Because of filesize problem, many web storage sites will only accept filess less than 1 Megabyte. That applies to our storage facility. Filesizes over 1MB will not be uploaded.
The answer is to amend the dpi, preferably when you scan. If you're going to send anything to a web site, I suggest you scan in 72 dpi - this will ensure that your image is generally OK for display on most computers and for storage in most web storage facilities, and will result in a reasonable file size (colour images can be a problem, though - in which case, scan at 72dpi and also reduce the physical size of the print).
A scan at 72 dots per inch (dpi) of an A4 page of 8.267in x 11.69in results in an image 595 dots (pixels) x 842 pixels so it will fit neatly across the screen while maintaining reasonable quality.
Because the physical size has remained the same, the printed size will remain the same - A4 - but the quality of the print will be much lower because your printer is only using 72 dots instead of say 300 - but it should still be readable (and you'll save yourself a lot of money because you're not using so much ink).