Michele,
We were pressing the submit button at the same time.
Chris,
I would recommend saving your original tif file as the source file and then make jpgs from that. Tifs are needed if you ever want to do hard copy printing. Tifs are very large and some people save them on CD to save hard drive space.
The dimension in pixels has something to do with amount of hard drive space an image consumes. But, as you can see in my examples, the dimensions were all 400 x 600, but dramatic differences in hard drive space consumed.
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