I've been doing some googling and reading on this for the past hour or so but it's about as clear as mud.

I noticed that the Canon 40d is defaulted to record in large fine jpg at 72 dpi. Although the actual pixels are huge and record at a high resolution, what about this 72dpi business?

Any of the forums I've read that discuss this all say "It's meaningless unless you intend to print". Ummmm well yeah that's kind of the point of taking wedding pictures.

I also found this, it sort of makes sense:
The 400D has a resolution of 3888x2592 in terms of pixels. As mentioned by several people already, the "72dpi" is irrelevant. If you give a uncropped jpeg file to a printing lab, and ask for 4"x6" prints, then, the linear resolution is: 3888/6=648 dpi, which will be more than the printer resolution of 300 dpi.

Does anyone know about this? Anyone printed a large file shot in large jpg? I generally shoot RAW and convert to jpg which gives me 350dpi but sometimes I just want to shoot jpg.

Anyone? Anyone? Beuller?

That's funny, my new Rebel does the same thing. I thought it was a setting that I had mistakenly made.

HMC150's - GH1 - Sony Vegas

Yeah me too.

But the math thing makes sense. If the pixels are 3888 wide for a large jpg then dividing that by 6 makes it 648dpi
To get a 16x20 it works out to almost 200dpi.
I think the 10d was set to 180dpi as a default. But it seems as though what the dpi settings are doesn't matter to the lab, it is the actual pixels itself.

Here's another forum post on the topic:

"since DPI is just a number in a digital file, and if you want it changed to be 300 - all you have to do is change it. Open the image in photoshop, go to Image/Image Size menu, make sure you uncheck "resample image" box at the bottom (you don't want physical size to change, just dpi), then change DPI box to whatever you want. It will also show you the new print size at that dpi... Alternatively, you may change one of the print dimensions, which will automatically adjust the second dimension and DPI, so that you know at what resolution your print will be coming out should you decide to print that specific size.

But again, keep in mind, that when you take your image to printing, the lab will ignore that dpi setting for as long as you tell it what size to print. The actual physical DPI will be whatever the number of pixels will lie on a linear inch of your print. So if you have 2592x3888 image, and you tell the lab to print a 4x6 photograph from it, they will print at 648 dpi, because 2592 pixels divided by 4 inches of length is 648 dots per inch. Same height-wise 3888/6=648...." This seems to make sense to me. I can't imagine why Canon would default the 40d to something low resolution.

Really, I guess the question is how big is a dot (dpi) because 72dpi isn't the same as 3888 pixels wide - unless you're printing really really big.

the DPI setting is really just a display setting for the most part. Monitors are 72dpi or (i think) about 96 dpi, depending on the model (newer have more dots). Inside the file is embedded a "viewing size" in DPI. When you print, you have different things to consider. A photo lab can get by with 100 dots per inch on the final print - or an 8x10 image needs 800x1000 PIXELS to print properly (bigger is usually better, though, but does not always make a noticable difference). Don't worry about the "dpi" setting registered in the file.

dpi is a term that is used for print. news papers are 65 dpi...hence a coarse dot pattern. Dpi has nothing to do with photographic prints. It's all about pixels. 4000 x 3000 pixels for instance. when you crop, just be sure to try to maintain the highest pixel count and forget about the dpi issue. However, if you are sending your work to a printer for 4 coolr printing, consult with that printer for specs.
hope this helps.Craig

Thanks. :)