Why Does The File Size Differ From the Image Size?

[sconwell]

While trying to set my new digital camera to match the size of the images that I had been taking with the old digital camera, I noticed different file sizes for the image, and not sure why! When I open the image in PhotoShop and go under "Image Size" the image is 14.4 megs and 2592 x 1944 pixels. Then, when I minimize PhotoShop and do a roll-over of the image in it's folder - with "Thumbnails" selected for view, it says the image is 1.78 megs. Why does this do this?

And a second question about the roll-over info: When I open an image in Photoshop and make any adjustments, then save it, the size seems to get smaller when I do the roll-over to check the size (like from 3.02 megs of a raw image, down to 1.78 megs if I open it and save it).

If I am too vague, I will be happy to elaborate on my situation. I would appreciate any explanation for this. My boss is thinking that I am doing something wrong to make the image smaller!

Thank you!

 

[DucatiST2]

When a file is saved compression is done on certain file formats, in photoshop the file is uncompressed and for each pixel there are three bytes RED,GREEN and BLUE so the file size is three times the pixel count. If you are editing the same document in needs to be in TIF,PSD or some other lossless format. If you save in JPG you will lose a lot of information.

 

[apepp]

..more here:

http://www.tek-tips.com/viewthread.cfm?qid=1469130&page=1

Andrew