PPI, DPI, croping help

[thewholequan]

Hello everyone,

I'm trying to wrap my brain around the whole pixels per inch/dots per inch.

I have a 6mp camera and when I download the image to the computer it says 3072x2048 pixels with a resolution of 72 ppi.

My printer is capable of printing at 300 dpi.

Now, I'm not that good of a photographer and I utilize the cropping feature heavily to make the composition look better than the original photo.

I'd like to know how much I could crop an image and yet still retain enough detail to print a 4x6 natively at 300 dpi? (1/4 the image, 1/8 the image?) Obviously, if I cropped a 1/32 piece of the original image there would not be enough detail to print a 4x6 at 300 dpi.

Along these lines...

How much can I crop if I wanted to ensure enough detail to print out a
5x7 @ 300 dpi / 150 dpi / 120 dpi
8x10 @ 300 dpi / 150 dpi / 120 dpi

I think I'm looking for an algorithm so I can apply it on a per image basis...

Please let me know if I'm going about this all-wrong.

[Bodog]

It's pretty simple really. Just multiply the size of your print (L x W) by the desired print resolution(ppi) to get your pixel dimensions. For example, if you want a 4 X 6 print at a 300 ppi resolution, then (4 X 300) x (6 X 300) would be a file 1200 x 1800 pixels. Forget the PPI number the image is tagged with; it's pretty meaningless in most instances. You mentioned that your printer will print at 300 dpi. That's pretty low unless you have a dye sub. Most inkjets today print at 1200 dpi and up. Remember a printer's dpi (dots per inch) is not the same as the image resolution in ppi (pixels per inch). Except, if you do have a dye sub, then ppi and dpi could be used interchangeably.