After a document is scanned I would like to crop a section of it and post it on a website at almost the same size as the document from which it was cropped. I would like to retain the clarity as the scanned copy too, so what can I do?
use this website to compress your scanned size
When enlarging a cropped image, the image is bound to pixelate. However, you can minimize the pixellation by increasing the quality of the scan by increasing the dpi (dots per inch). Generally, scanners range from 150 dpi to 300 or more. So for the best results, increase the dpi in the scanner settings. Keep in mind that the higher resolution of scan that you select, the longer it will take to scan the image/document.
Scanner software I've used first does a preview scan. From this you can select the area you want to scan, resolution etc. and then it scans that cropped area. Thus you don't lose clarity as you would in method you describe.
I m afraid that cant be done for if you would enlarge a pic, you would definitely lose some quality....try posting the whole of it to retain the clarity...
If I understand your question correctly, you want to enlarge the image so that the cropped section will be the same size on screen as the entire document was on paper. Normally, if you scan for the purpose of reprinting you would scan at 300 DPI (dots per inch). Since screen resolution is usually much lower (72-100 DPI), this means that a 300DPI scan is in fact "enlarged" by a factor of three or four, so all you need to do is open the image in your favourite image editor (IrfanView is good if you are looking for one), crop the image and save it, then upload it.
If the section you want to crop is very small (say, smaller than a quarter of the original size), then start by scanning at 500 DPI.
try to convert to jpeg then crop with photoshop, irfanview
You should scan the image with a high dpi then it'll be clear!
cropping will retain the size, I don't think you need any other, if you are planning to enlarge, then scan it in png format, which gives good clarity even after zooming.