Confusion about image resolution and dpi

[marchael]

Okay, perhaps I'm just having a pre-senior moment here but some clarification about this matter would be very muchly appreciated.

I use a Canon Digital Rebel XT and shoot at the highest resolution setting, Large Fine. The images are 3456x2304 pixels. Someone who is interested in my photos needs to print them (I'm only sending the digital files) approximately 5x7 inches at 150 dpi or greater. When I check the images' properties (right click, properties) the resolution is listed as 72 dpi. Am I missing something as far as setting the resolution to be higher than 72 dpi or is it something that needs to be done in post-processing? This is baffling me.

Thanks,
Mark

[castledude]

Nope you are right, it's a post processing option. Almost all the digital cameras fill in that field with 72.

Most post processing programs will allow you to reset it to whatever value you want. Most home printers allow you to ignore the value.

The only ones that care are the professional houses that still think in inches at dpi rather than pixels.

[gemmf]

Yes, cameras are normally set at default 'ppi' (not 'dpi' which is to do with a printer). I know it's not possible to change it in my camera, so I change it in Photoshop. It can be done in 'Image Size', then set the required pixel/inch (while unticking 'Resample Image').

[dougj]

As mentioned, the 72 DPI value is misleading, and causes a lot of confusion. The only thing you need to do with your photos is a little cropping as the aspect ratio from the camera is not the same as a 5 x 7 photo. This can easily be done with photo editing software. When cropping, set the parameters in inches and do not "resample".

Your final images will print with a resolution of about 460 DPI without any additional processing. This is considerably higher than what you really need for a high quality print.

Here is an article that discusses DPI vs. PPI, I suggest you read the section "The Horrible DPI Mistake"

http://www.rideau-info.com/photos/mythdpi.html

And another by the same author on what the printer needs.

http://www.rideau-info.com/photos/printshop.html

[marchael]

Thanks castledude, gemmf, and dougj for your help.