Why 72 dpi in Photoshop

[scubi]

Hi
I have just received my 10D, wow what a camera. I can see my results straight away. Fantastic. I am like a kid , with a new toy.
My question is, I have taken a couple of photos and downloaded them to my pc and I have opened them in Photoshop.
When I look at the file size it shows( Document size ) Pixels/Inch is 72.
That will not be enough to send it to the lab for printing.
Should it not be about 600 DPI ?
My camera quality is to Large/Fine.
Thanks
Vaughan

[Roger_Cavanagh]

Vaughan,

72 DPI is just a default value that is assigned to JPGs. Just change the value in PS to something more suitable for your printer: 240/300 would be sensible choices. 600 would probably not work well, you just waste ink when printing.

Regards,

[ce900a]

hey first time post yeaea! anyway so when you go into the PS prefrences and change the dpi there are 2 selections a screen and print dpi. my print dpi was set at 300 but what should the screen be set to ???? It's always been set at 72dpi, just curious.

ce900a

[Jesper]

The DPI number has no meaning at all. It's just a kind of suggestion for display on a computer monitor.

A digital image consists of a rectangular grid of pixels. In the case of the 10D, you have 3072 x 2048 pixels when you set it in the highest resolution mode. The size in pixels is all that matters.

The number of dots per inch (or pixels per inch) only has meaning when you print the image at a specific size. For example, if I print a 3072 x 2048 image at 300 pixels per inch, the printed image will be 3072 / 300 = 10.24 inches wide by 2048 / 300 = 6.83 inches high.

[Littlebike]

When I go to "Image-Image Size" mine is always 180dpi.

I just went to "Edit\Preferences\units & rulers" and my display is set to 72 display, 300 print.

I suppose this is right, is it?

[Webster]

You would have trouble getting that 72 dpi picture printed, anyhow. If a 10D's picture is set to 72 dpi, its size is set to 42.667x28.444 inches. If you own a printer that can print to that size, you already know better, and if you send it out to get it printed they will either just reset the size and resolution for you, or educate you.

If you reset it to 600 dpi, the size becomes 5.12x3.413. Not exactly what you'd expect.

Remember that a digital image is just a matrix of dots, and those dots can be either scrunched together when rendered visually to give a small picture or spread wide apart to give a large picture. There is no size inherent or implied in the matrix.

By the way, 72 dpi was the resolution of the original Macintosh, and Photoshop was first developed on that system.

[NickC]

webster wrote:
By the way, 72 dpi was the resolution of the original Macintosh, and Photoshop was first developed on that system.

72 units per inch (six picas) in the typography, printing & graphics industry long preceded computers. I would like to think that Adobe/Apple decided to use 72 dpi on monitors/displays/software because of that.