Working with digital images

[Boxgrover]

I have a Canon S2...5 megapixels I think. I noticed looking at the details of a couple of pictures that I recently took...completely unprocessed, that the file size was 4.2 mp! I didnt think that was possible   I am accustomed to seeing files sizes from 2 to 3.5 tops. I am wrong?

[ShutterbugGail]

Yes, that's possible. File size varies according to the amount of color in the photo. For example, if you took a black and white photo, it would be a smaller file size than the same one shot in color.

[pentachris]

At 2492x1944 and 24 bits per pixel, the impossibly large file size would be something greater than 14.4 MB.

2492*1944*24= 120932352 bits

120932352 bits/8= 15116544 bytes

15116544 bytes/1024= 14762.25 KB

14762.25/1024= ~14.4 MB

Plus a little for metadata (exif info, etc).

The jpg compression reduces the file size by looking for patterns, blocks of color, etc.  More color and more complexity are harder to compress without losing quality, so the file sizes for them will be larger.

More related info:

http://computer.howstuffworks.com/file-compression.htm

http://computer.howstuffworks.com/question289.htm