Canvas Size?...Image Size?...Resolution

[CascoGraFX]

I guess what I need is something that one of my 6th Grade grand daughters could understand (and explain to me). In PS7, I have a nice little photo that is 72dpi and is about the size of a business card. I have a flat-bed scanner (HP4470c) attached to my computer. Between PS7 and the scanner, is there any way that I can print this photo as, say, a 5x7 without the jagged-edge effect? I guess what would be most helpful in understanding this would be the relationship between all of the elements involved: DPI<>Image Size<>Scanner Resolution<>Printed Size. The help screens with Photoshop engender more questions than they answer. Can someone just point me in the right direction? Is there a book (with pictures, preferably) - something on the order of "Photoshop For Old Dummies"? Thank you very much.

[Doug Nelson]

Your photo is not 72dpi, it is 72ppi. There's a difference, though the marketers at the printer and camera companies don't seem to know it. Images are made out of pixels and prints are made out of dots. You can print a 72ppi image at 1440dpi, it will represent each pixel with 20 dots (which is good, since each dot can only be cyan, magenta, etc., and this allows for more colors to be represented.

Avoiding the jaggy look you refer to is a function of how many pixels there are in your original image vs. how wide a print you're spreading out those pixels. The wider the print, the larger each individual pixel must be, and if they get too large, you can easily see them.

Generally, you'll want more than 150 image pixels per final printed inch to avoid "jaggies" or "stairsteps", etc.

[Vikki]

To put it in a nutshell, if you enlarge the image, it will look blurry.
Here's a little example I made up:

[CascoGraFX]

Thanks to Vicki, Doug and RonDon's e-mail, there is hope for me yet! It don't take more than one swipe up side the head with a tire tool before I begin to understand. Thank you, one and all.