DPI

[Tighearnach]

Hi

A friend gave me some jpegs that I want to print off. How do i figure out what DPI a file is? I know it needs to be around 300 to blow up.

Also at what point during processing does one usually choose the DPI of a file. If you shoot in jpeg does the camera have an automatic/standard dpi for each shot or do you specify that later?

Regards
T

 

[ANDS!]

A file doesn't "need" to be anything to be stretched or smallerized - the aesthetic results will depend on the user. However, some people follow a hard and not at all fast rule that anything below 250 is unacceptable; some wont even go below 300. It's all up to you really.

If you right click on the file, and check Properties>Summary you should see the current DPI of the file.

 

[Big Mike]

Don't worry about the PPI (Pixels per inch is technically more correct that DPI...which is a function of the printer).

What you should do, is check the size of the image, in pixels. That will give you an idea of the size of the print you could easily make. Some people use the 300 pixels per inch of print standard but you can still get good results with less.

 

[epp_b]

DPI/PPI is a measurement of print resolution, not overall resolution. 300 DPI is considered fairly standard for good quality prints. The D40 sets DPI at 72 by default, which would print at 30x40", but I've never tried printing that large.

I like prints as good as possible, so I'd set the resolution as high as you can go for a given print size. Eg.: a 6MP (3008x2000) image can print at about 250 DPI.

Keep in mind that, the bigger you print, the further away you'll be standing from the image when you're viewing it. It's won't be directly proportationate (you'll eventually hit a point were you just can't go any larger), but you can go a fair ways down in DPI and still have an acceptable print.

 

[Tighearnach]

So as an example, if I have a print that is

3888 X 2592 pixels

how many pixels per inch is this?

Also I have two jpegs both taken with a digital camera and both having the above measurements however when i go to properties one says it is 150 dpi and the other is 350 dpi.

Would this have occurred when converting from raw to jpeg?

Could both technically be blown up to the same size?

Thanks for any help
Tighearnach

 

[Big Mike]

I would suggest that you forget about PPI. It's really only a number that tells the computer how large to display the image on your monitor.

You could set it at 100 or you could set it at 10,000...and as long as your image is still 3888 x 2592, there won't actually be any difference.

For example, at 300 PPI the size would be 12.96" x 8.64"...when viewed at 100% on the computer screen. At 150 PPI, the image is twice as big on the monitor but it's still the same quality.

The reference for printing is 300 pixels per inch of paper...so with that, you could print at 12.96" x 8.64"....but you could easily go bigger if you wanted.

Again, Dots per inch has to do with ink on paper...not digital files.

 

[Tighearnach]

I suppose the one drawback i have found to digital photography is that i rarely print. As a matter of fact I have never printed anything since i got my DSLR one year ago! But thats just cos my photos are crap!

So i am totally green when it comes to this end of things. Will need to read up on it or something.......

As always thanks for all the help.....