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Yisehaq
08-16-2010, 02:11 AM
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,

Marko
08-16-2010, 08:42 AM
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

Iguanasan
08-16-2010, 09:05 AM
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/4080/4889075321_83b81fdee2_m_d.jpg (http://www.flickr.com/photos/eulothg/4889075321/) , 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.

Yisehaq
08-16-2010, 09:40 AM
Thanks Marko & Inguanasan.
Wow, I thought I was missing something but didn't know that I was completely in the dark.

Yisehaq
08-16-2010, 10:01 AM
Just curious?!?! Is there anything like boosting pixels so that one can print the picture in a larger format?

Iguanasan
08-16-2010, 10:58 AM
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.

Marko
08-16-2010, 11:37 AM
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 (http://www.alienskin.com/blowup/index.aspx) 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

JAS_Photo
08-16-2010, 01:42 PM
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 (http://www.danrichard.com/2006/03/23/to-print-or-not-to-print-making-sense-of-the-dpi-equation/)

Yisehaq
08-17-2010, 01:55 AM
Thanks Inguanasan, Marko and JAS. I get the point now.

casil403
08-18-2010, 07:52 AM
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. :)

Iguanasan
08-18-2010, 08:03 AM
While the article JAS pointed to which states computer monitors are not actually 72 DPI is true, it is also very true that they are very close to it. The 72dpi or 96dpi is based only on one of the dimensions which I believe is the vertical dimension. So, most people will see your images in and around 75dpi, a few - very few - will have adjusted their monitors to 96dpi but that would be the exception rather than the norm.

Most people who are publishing for the web will ensure that they publish at 75dpi for the very reason you wish to do so.

casil403
08-18-2010, 08:09 AM
WOW...I am surprised one can go that low. :thumbup:

Iguanasan
08-18-2010, 08:22 AM
Compare for yourself:

300dpi
8839

200dpi
8840

96dpi
8841

75dpi
8842

casil403
08-18-2010, 08:40 AM
PERFECT!! :thumbup: :thankyou: Iggy!

Marko
08-18-2010, 09:13 AM
As far as i know.....DPI doesn't matter for the web. (unless you are posting full Jpeg files or very high res files that are ready for printing).

As far as i know, it's all about filesize for the web...because we DOWNGRADE our images (save as Jpeg, then we say what quality of jpeg) before posting them. (most of us anyway).

If I save an 800 pixel wide file at a medium Jpeg quality so that the end result is about 100-150K....that file will look bad (to me at least)when printed whether it was 300DPI or 72DPI.

DPI is mostly about printing. Pixels and filesize are the parameters for the web.

Just to reconfirm this, I printed 2 of Iggy's 81k files (one at 75 dpi and one at 300 dpi). Because the file was compressed to 81K, both versions look equally bad and i cannot tell which is 300 which is 75dpi. :twocents:

Iguanasan
08-18-2010, 09:36 AM
Hmmm.... Looks like I'm talking through my hat. I thought for sure DPI had some effect on the screen as well but now I'm thinking it only matters when you print. Been playing with different DPI settings here and it looks as though, for the screen, you see the image at about 75dpi, however, that has actually no impact whatsoever on the printing of the image. You can take the same image and print it at 20dpi or at 600dpi and it will effect the size on the paper, however, it doesn't effect the detail in the image.

So, it's about dimensions. If you give someone a full size 4000x3000 pixel image they have the capability to print a decent size at a reasonable high quality. If you only give them an 800x600 image then they are locked into an image which they can only print to a certain size. DPI information in the image is completely meaningless unless you print it.

Learn something new every day! :)

Marko
08-18-2010, 09:49 AM
So, it's about dimensions. If you give someone a full size 4000x3000 pixel image they have the capability to print a decent size at a reasonable high quality. If you only give them an 800x600 image then they are locked into an image which they can only print to a certain size. DPI information in the image is completely meaningless unless you print it.

Learn something new every day!For the web, again as far as I know - It's about dimensions AND filesize. If EITHER the 4000x3000 file OR the 800x600 is saved as 100% jpeg ( yielding LESS compression in the final file), you'll get respectable results if you try to print from it. Of course, those file sizes will be large. The 800 pixel file might be 700k to 1 meg, the 4000 file could be 15-20 megs. Some people DO INDEED upload in that quality for the express purpose of allowing people to print the photo. But for the purposes of protecting your work by uploading lower resolution files, don't worry about the DPI just save the file at a medium to lowish jpeg.

and I agree, DPI information in the image (for web use) is completely meaningless unless you print it. I do not believe I can see any difference in any of your 4 posted files Iggy. For the web, 81k is 81k when the dimensions of the file are identical.