Q. on DPI and printing

This is a bit of a random question...

I know 72 dpi is for web use, and 300 dpi is for printing. If I were to save an image with 72 dpi, and then later go in Photoshop and change it to 300 dpi, is that possible, or is it already saved as 72 and cant be changed again? (just like when you change image dimension sizes, it can't be undone without looking pixelated). If I were to print that 72 dpi from an inkjet, the quality would be lousy, correct?

hehe just checking. I am trying to do a composite image with a photo I took out of my camera, to paste it in a shot (found online) from a movie still, and then print it, but am thinking the shot from online will look bad quality since it was probably saved as 72 dpi.

I hope this even makes sense!

Dpi is only part of the equation. More important is the image dimensions in pixels. Dpi (actually ppi) can be changed to any number you want without altering the image. Divide the pixel dimensions by the ppi you want to print at to determine how big the printed image will be. For instance, a web image 600 X 600 pixels will only make a print 2" X 2" printed at 300 ppi.

Hmm interesting! Thanks for your reply! I'm not very good with matimatical equations, so how big might I be able to print something that is 800x600? (I'm guessig about 3x2 inches since you said 2x2 inches for 600x600) What about 1024x768?

Grr that's not very big to print it though

Just divide the dimensions by the intended ppi. 800 X 600 is 3.67" X 2" at 300 ppi. Also, remember you may not need 300 ppi, depending on the intended use and printer quality. 200 ppi may be OK. If you're printing yourself, experiment. You can also try re-sampling the images to a larger size in Photoshop or whatever image editing app you use. You'll need sure to do some sharpening after re-sizing.

Cool beans! Thanks Bodog!

DPI is just a factor of print quality you can get with the size image (pixel count) you have. And web images aren't 72dpi since they are on your screen and will have to be 1 pixel = 1 pixel on your monitor display resolution e.g. 1024x768. This is why you have to resize your images for web viewing or do a 100% crop. Otherwise many images would be bigger than your screen, as they are when viewing at 100% in PSE.