How do you change the dpi of a photograph?

Answer 1

I can only partially answer this, because in my view there are several factors.

1: In the camera you can set the resolution of the photo when it is taken. Stretching that photo to fit a certain print size will then result in a certain DPI. 2: You can resize a photo in an editor. But use caution, as there are different resize methods. Some result in better quality than others. It is possible to end with an image which says it has a high DPI value, but the content is actually low in pixels. So you have wasted file space and you still end up with larger pixels than necessary. And last, you can keep the file large and wait to scale it until you are ready to mail or print. At that time you should be able to select the dimensions in inches or cm.

I rarely pay attention to the actual DPI value becaue the result can be unpredictable and dissappointing. Instead, I prefer to stick with pixel dimensions and let the DPI adapt as it may.

Are you are trying to change to a smaller or larger format? What are you starting with and is it the screen size or printing size you are concerned about?

-srobidoux@Verizon.net

Answer 2

You can use a variety of tools, from simple image editors (like the classy MS Paint) to dedicated image converters. Free or commercial tools.

I suggest giving AZImage a look (see reference) - it is a simple image converter supporting also advanced options if you decide to fine tune the results.