what do you mean by "72"? Is that the DPI of the images? (72 is the standard DPI for JPG)

Actually, the resolution is not 72... that is ppi.  The resolution is going to be something like 3072x2048 on a 6MP camera.  I have a Fuji S3 and it stores its JPEGs at 72ppi but if I resize it to 300ppi then the picture size changes but not the resolution.  Visit this web site for more info. 

http://www.usefilm.com/article-14-Understanding-Resolution.html

When capturing and editing your images try to not to think of the output resolution of the printer i.e., 200dpi, 300dpi etc..  Rather, think in terms of pixel dimensions like 3500x2300.  Printing resolution doesn't mean much when editing an image that hasn't been printed yet. When you're ready to send an image to the printer you will then need to change the file to the printer's resolution, which in the case of mpix is 250dpi. 
 

Some of you are very confused about ppi and dpi...

I usually recommend you start here: http://www.fotofinish.com/resources/centers/photo/resolution.htm 

The 72 dpi you see is virtually meaningless.  It is based on the monitor, which is "usually" 72 dpi, although many of us are running higher resolutions than that. I think that I am at 96 dpi.

The short version is that the size of your image determines what you can and cannot do.  You do not have to upsample in photoshop for most printing applications.  Let's use the Rebel as an example since that is what she owns.  I believe it is 3456 x 2304.

That means that if you want to print at 200 dpi, you could print an image that was 3456/200 = 17.28 inches x 2304/200 =  11.5 inches.  At 300 dpi you would have 3456/300 = 11.5 inches x 2304/300 = 7.7 inches.

Basically, you'd have to start printing significantly above 18 x 12 inches before resolution became a factor with a Rebel XT. 

"You can achieve photo quality results when using as few as 150-200 dots-per-inch (dpi) images. The basic rule to maintain image quality is that the number of pixels in the image bitmap file must increase as the size of the printed picture increases. Otherwise, individual pixels will become larger in the print and the picture will get a jagged and grainy texture."

While you're correct that you don't have to upsample a photo to print on an inkjet, I use commerical printers and output that require 300dpi so I must upsample for certain products. By the way, there is really no limit to the size of a print you can make due to the drivers in printers. I've owned sub-megapixel cameras and made quite large prints from them that turn out great with no upsampling...it's purely the quality of the printer's driver that makes the difference. Your web reference only talks about printer dots-per-inch, but does not mention the printer driver's ability to dither the missing information required to make a quality print. It's written assuming that the photographer will upsample/downsample their image to match the intended print size. What I'm saying is that your camera operates at 72dpi when the files are extracted from the camera, only the number of total pixels change when you buy a new, bigger camera. Total pixels does not equate to dots per inch or pixels per inch. Your printer prints at 300dpi (or whatever it's default is) and it's driver fills in the gaps when you don't send a 300dpi file to it.

If you tried to provide enough pixels for a 1:1 ratio in a 20x24 print @ 300dpi, you'd need a 43MP camera. Yet, I have beautiful, flawless 20x24's printed at 300dpi made from my 8MP camera. Where did the extra data come from to make the print? The lab's printer driver! My camera provides less than 1/13th the necessary data, and the driver fills in the "holes".

If you'll open a photo in Photoshop directly from your camera, you'll see that the dpi is.

Tom_Steele:

Some of you are very confused about ppi and dpi...

I usually recommend you start here: http://www.fotofinish.com/resources/centers/photo/resolution.htm 

The 72 dpi you see is virtually meaningless.  It is based on the monitor, which is "usually" 72 dpi, although many of us are running higher resolutions than that. I think that I am at 96 dpi.

The short version is that the size of your image determines what you can and cannot do.  You do not have to upsample in photoshop for most printing applications.  Let's use the Rebel as an example since that is what she owns.  I believe it is 3456 x 2304.

That means that if you want to print at 200 dpi, you could print an image that was 3456/200 = 17.28 inches x 2304/200 =  11.5 inches.  At 300 dpi you would have 3456/300 = 11.5 inches x 2304/300 = 7.7 inches.

Basically, you'd have to start printing significantly above 18 x 12 inches before resolution became a factor with a Rebel XT. 

 

RVsForFun:

While you're correct that you don't have to upsample a photo to print on an inkjet, I use commerical printers and output that require 300dpi so I must upsample for certain products.

I'm not arguing with you, but I am saying that YOU don't have to upsample until you reach image sizes of over 11.5 inches x 8 inches - roughly speaking.  The camera is putting out 3456 x 2304 pixels, and dividing by 300 pixels per inch, you arrive at those numbers.  Also, I don't know what the OP's intended application is, but if it is here on Mpix, then 180-200 ppi/dpi is fine for most photographic printing which means most of us can go way past that and into the 16x20 range before seeing softness.  And actually, you can get away with sloppier ppi/dpi's on larger prints because who looks at a 16x20 from the same distance they view an 8x10? 

By the way, there is really no limit to the size of a print you can make due to the drivers in printers. I've owned sub-megapixel cameras and made quite large prints from them that turn out great with no upsampling...it's purely the quality of the printer's driver that makes the difference. Your web reference only talks about printer dots-per-inch, but does not mention the printer driver's ability to dither the missing information required to make a quality print. It's written assuming that the photographer will upsample/downsample their image to match the intended print size. What I'm saying is that your camera operates at 72dpi when the files are extracted from the camera, only the number of total pixels change when you buy a new, bigger camera. Total pixels does not equate to dots per inch or pixels per inch. Your printer prints at 300dpi (or whatever it's default is) and it's driver fills in the gaps when you don't send a 300dpi file to it.

I'll generally agree with that.  However, if you send a low dpi/ppi file - AT THE PRINTING SIZE - to a printer, I think the driver will give its best shot and end up looking kind of crappy.  For example, if you send a 640 x 480 image to your printer and tell it to print an 8x10, you will be at ~60dpi/ppi and you will have a bad image, even if the printer driver tries to fill in the gaps. 

If you tried to provide enough pixels for a 1:1 ratio in a 20x24 print @ 300dpi, you'd need a 43MP camera. Yet, I have beautiful, flawless 20x24's printed at 300dpi made from my 8MP camera. Where did the extra data come from to make the print? The lab's printer driver! My camera provides less than 1/13th the necessary data, and the driver fills in the "holes".

I think you are just looking at it from a different perspective.  If you send an 8mp image and have it printed out at 20x24, then one of two things is happening.  Either your lab is upsampling and printing at 300 dpi as you say, or you are getting an image that is around 144 dpi and that is within range of acceptable.  Especially since a larger photo is usually viewed from a farther distance.  Ultimately, I suspect that all labs print at their native resolution and upsample if you aren't there.  In the end, the result is the same.  The labs are telling you the lowest dpi for that print size that they can upsample to a decent looking image.  Mpix has stated in their faq that 180-200 is the minimum target.  I've printed 11 x 14's off of a 5mp camera and they looked fine to me.  If I hold the print up to my eye, I can see softness.  But if I mount it on the wall and view it normally it looks very good.

If you'll open a photo in Photoshop directly from your camera, you'll see that the dpi is.

DPI is entirely arbitrary.  It is a flag that is set by the camera, or your image editing program.  It is meaningless when the image is captured.  The only thing that has meaning is the size of the image.  Once you have the image captured, then ppi/dpi only become meaningful when you try to print very large and exceed the possible ppi/dpi of the image for that size print, or if you are putting the image into another setting.  On the internet, it doesn't really matter because you can set the image size in your webpage formatting, thus forcing the image size regardless of the final ppi.

People make far too much of ppi/dpi.  Basically, ignore it - UNLESS you are printing very large, then figure out if you are too large.  Otherwise, it does NOT matter what your dpi/ppi is set at when you go to print, if you are using the original sized file from your camera.  And in fact, many people SCREW UP their images by setting ppi/dpi because they don't know what they are doing and set an image size and a ppi/dpi and throw away pixels.