What determines the size of your print?

Hey all,
I just wanted to ask what determines the size of a print? Is there any rationale to follow when you think of printing your photos?
cheers,

Indeed there is. First thing to check is the size of the FILE.
Open it up in a graphics program and somewhere it should tell you how big it is in pixels (for the web) AND how big it is in inches or centimeters (printing size)

Of course this is 100% related to the QUALITY of the capture. Ie a RAW file will capture more info than a jpeg. Thus it's filesize will be larger, thus you can print it larger.

Another thing to be aware of is WHO will print the image. If it's you, no worries. But if it's a lab, they may well have a format that they print in. If your cropping is non-standard, they may want to charge you more, convert the image to a standard size, say no we can't do this like this, etc.

Hope that helps - Marko

The size of the print is really determined by math. Probably didn't want to hear that, eh? ;) Take, for example, the full size original of this print, http://farm5.static.flickr.com/4080/...1fdee2_m_d.jpg , it's 3690 x 2493. Computer monitors are generally about 72dpi (dots per inch). So, 3690 / 72 = 51.25 inches and 2493 / 72 = 34.625 inches or about 50 x 32 on a monitor. Now, let's take a look at actually printing it. Your average laser printer is around 300dpi which means that same image will print at about 12 x 8 at that resolution. That's not saying you can't print it larger it's just that the quality will suffer as there will be fewer dots per inch. Glossy magazines will generally print at about 600dpi and some at 1200dpi so the same image would print at 6x4 or 3x2.

There's one more thing that enters into this and that's interpolation. Note that you can print this image at 600dpi and tell it to print at 12x8. The computer will interpolate (compute an average) for the missing pixels which may be fine or may make the print look crappy. It depends on the original quality of the image as Marko was saying.

Thanks Marko & Inguanasan.
Wow, I thought I was missing something but didn't know that I was completely in the dark.

Just curious?!?! Is there anything like boosting pixels so that one can print the picture in a larger format?

You can always print larger but the larger you get the more detail you lose. There becomes a tipping point where the image no longer looks good. This is why it's so important to get the image right in the camera. You can add pixels through interpolation to make larger prints but you can't create more detail in the image. You need a very sharp clear image with lots of pixels to get very large prints.

You CAN indeed upsize the file somewhat as Iggy suggests, but you have to be careful about how much. I do this using Photoshop occasionally, and I'll usually upsize in increments of 10%. I might do this 2-3 times on the same file...

I know alien skin also has a product that does this but i have never tried it.

There is a BIG difference however between how the image looks on a computer screen when you upsize versus when it is printed. The printed version is the one that counts, so if you have an inkjet you should do a few tests.
Best! - Marko

Here is an article that helps explain dpi which is important for printing. What Iggy and Marko have said is true this is just a little more detailed.

Learn how to use the right DPI for Printing or On-Screen Graphics – Making Sense of the DPI Equation » Tutorials, Articles and Ramblings by Dan Richard

Thanks Inguanasan, Marko and JAS. I get the point now.

So here's my question and I am posting it here as it it related to the original thread. Thanks Yisehaq. :)
What is the lowest DPI/PPI one can post at 800p on a computer before an image becomes pixelated?
What is the DPI/PPI size most people use when posting images online?
I ask this because I want to keep the resolution on my images as low as possible copyright infringers. They can get the image but cannot do much with it.
Right now I have it at 245ppi but I want to go as low as possible without compromising image quality.
Thanks. :)