How do I get a 300 dpi image from my 7.0 MP camera?

Question

I have a fairly new Canon digital 7.0 MP digital camera. I'd like to put together a catalog for my business. My printer wants 300dpi for quality.
If I set my camera at the highest setting, I get a 3072x2304 pixel image at 200dpi.
I'm very confused with this whole DPI/PPI/Megapixel issue...

Can I actually use my own images from the camera to achieve 300dpi? Does shrinking my image increase the DPI? If, yes what is the largest size I can get at 300DPI?

Maybe if someone could explain this whole calculation. :)

Thanks.

Answer 1

Resolution - PPI vs. DPI

The easiest way to find out what you have is to take a picture.
Open the picture in Photoshop or Photoshop Elements.
Click on "Image" then "Resize" then "Image Size"
(Or use [CTRL]+[ALT]+[I] < Look at "Resolution" on the window that opens and it will show you what the resolution of the image is.

You can not control the pixels per inch in your camera, as this is a function of the sensor. I have found the following ppi for SOME cameras by the following manufacturers. I wonder if this specification is available anywhere. I have four camera manuals in front of me and I can't find it in any of them.

NIKON - 300 ppi
CANON - 180 ppi (Plus your reported 200 dpi.)
PENTAX - 72 ppi

We "discussed" this by way of question and answers a while back and decided that the ppi file produced by the camera really did not have any effect on the capability to produce a good print. If I take a photo with my wife's 6 MP Nikon and view the image on the screen, it will start out as 300 ppi. If it's a full frame image of 3008 pixels x 2000 pixels, the SCREEN image would be pretty big if I viewed it full sized, but it would print 10.0" x 6.6". If you crop a 5x7 out of this, keeping it as full-frame as possible, it becomes 400 dpi.

With my brother's 6 MP Pentax, the image is 2816 px x 2112 px, but it's at 72 ppi. If you print this without cropping, it would be 39" x 29"!!! If you crop a 5x7 out of this, though, it becomes 402 dpi resolution, which is virtually identical for the Nikon 6 MP camera.

With my son's 6 MP Canon Powershot A620, the image is 3072 px x 2304 px, but it's at 180 ppi. If you could possibly print this without cropping, it would be 17.1" x 12.8". If you crop a 5x7 out of this, though, it becomes 439 dpi resolution, which is a bit better than either of the other 6 MP cameras.

In other words, regardless of the sensor's pixel-per-inch output, 6 MP cameras produced the same resolution when it came time to print comparable images. How about a camera with more pixels?

If I take a photo with my 10 MP Nikon D200 and view the image on the screen, it will start out as 300 ppi. If it's a full frame image of 3872 pixels x 2592 pixels, the SCREEN image would be pretty big if I viewed it full sized, but it would print 12.9" x 8.6", if I had the right paper. If you crop a 5x7 out of this, keeping it as full-frame as possible, it becomes 516 dpi, or higher resolution than the 6 MP cameras. We knew that is would work out like this, though, didn't we?

The REAL question is, what difference does this make in the real world? If we agree that 300 dpi is an excellent resolution for prints, as long as you end up with at least 300 ppi after you are done cropping on the screen, you will get an excellent print as far as resolution goes. All four cameras exceed that amount. I usually resize "down" to 300 dpi before printing, because you can't tell the difference above that resolution anyway. Most people would be quite happy with a 200 dpi print, so go ahead and crop a bit. If you get a print resolution too much below 200 dpi, you will start to see digital artifact in the print and it will be objectionable.

Answer 2

The default dpi that your camera outputs doesn't mean jack. The only thing that matters is the number of pixels that you send to the printer. If you send him a 3072x2304 file, he can print it at 300 dpi with a resulting print size of
width: 3072 pixles / 300 dpi = 10.2 inches
height: 2304 pixels / 300dpi = 7.7 inches
He can also make a smaller print if he wants. But he can't make a bigger print - not without pulling extra pixels out of his asshole (the technical term is interpolation) or reducing the dpi setting.
(3072x2304 pixels = 7,077,888 pixels = 7 megapixels)

Answer 3

Ok, there is a difference between dpi and ppi, but most people and cameras get them turned around.
dpi stands for dots per inch.
ppi stands for pixels per inch
when you look at the properties of a picture from a camera most of the time it will look something like this
2592 x 1944 at 240dpi (thats a typical 5mp)
now that 250dpi number says very little about what your getting.
Most pros say that in order to get a photo quality image from a digital, you need at least 300ppi. That means the pixels are small enough at that point that you eyes don't see them.
Going back to the 5mp (2592x1944) at 300ppi that will give you a 7x5 or 5x7 print. There are always ways to fudge those numbers to get larger prints. Magazines are printed at 150-200ppi so now with the 5mp numbers you just went up to 17.25 x 13 print size.
The really high end pro cameras will make a pic that says it's only 72ppi. It just takes a little math to figure out what the true size of a print will be.
Also just a note... most moniters only display at 100ppi. Don't worry about what you printer is asking for, at 7mp camera should give you great prints up to 11x15.

Answer 4

You can use Photoshop to resize (change) your picture to specific DPI.