We, meaning me, use DPI to describe resolution for all things. I should not do this but I probably will continue to refer to all things as DPI.
Meagapixels—Millions of pixels describes camera resolution. And yes, they tout the number of meagapixels to confuse you. High is good but when looking for a camera try to find the number of effective meagapixels. Effective megapixels are the number of pixels used to actually capture the image. A nice point and shoot over 4/6 megapixels will do you fine. A 4/6 will do fine but a little higher will produce a nice image for the occasional enlargement.
PPI—Pixels per inch refers to image file and monitor resolution. I usually recommend web image files be saved at 72 DPI ( I know, I know—just know the 72 part). However, monitors have higher resolutions so 72 is fine but if you want a really sharp image try 85 or 125. If you use a higher resolution be mindful of the size. Large files can still take a long time to load. As far as image file size goes the higher PPI means the image contains more information and can be made larger and still look crisp.
DPI—Dots per inch. This means how many dots of ink will be placed on the paper by a printer. The printer being inkjet, laser or commercial. Higher isn’t always better here either. You can have an image that is 1200 DPI but if your printer can only print 600 or more often 300 DPI it will resample (rewrite) your file and discard the extra information. You and your imaging software are much better at determining what stays and what goes in your image.
FYI: Newspapers are printed using LPI or lines per inch and generally are printed at 85/100 LPI. Ay yi yi.
Time to understand a little more about resolution. The fundamental truth still applies though time goes by, a low resolution image cannot be made into a high resolution image. Well it sort of can, but it will be a teeny tiny picture. Resolution is how close pixels are, pixels by the way, are the blocks of colors that when viewed at a distance create an image. Your monitor has a resolution of 72 (dpi—dots per square inch as left over from print, just go with it). Your monitor will show you your image at 72, no matter what. But what if you want to print? A little more explanation before that bit. Higher resolution yields a clearer sharper picture but at a smaller size. Lower resolutions results in a less distinct, blurry, pixilated picture but at a larger size. If you have a 3 x 5 image at 72 resolution you can’t make it 300 without it getting very small. If you want it to stay the same size, if your software permits, it will resample. Resampling is when your software gets rid of information it doesn’t need (300 to 72) or creates information (72 to 300) to reach your desired resolution. Except to create information your computer software guesses based on the information of adjacent pixels. It looks bad so don’t do that. What about printing? Your printer likely has a print resolution of 300. If you send a 600 resolution to your printer it will resample the image. Don’t let your printer do that, you change the resolution to 300. You and your imaging software will do a much better job.
Print–ready Pdfs what are they and what does it mean? I get requests all the time for, “high resolution Pdfs.” And what is exactly is that? You see, when saving a file as a Pdf you have many options. Among them are print–ready and press–ready, there’s web too but that’s for later. When I see a designer asking for a, “high resolution” Pdf I think they don’t know what they want. I try to figure out how it’s being printed and send them what I think they need.
But here it is in a nutshell; print–ready is for things that will be printed out on an office printer or at a copy shop. Saving Pdfs in this version will produce good quality printed material for handing out. This might even include a short run brochure or flyer that you might want to run off in–house. Press–ready is for things being sent to a commercial printer. High run digital printing or offset printing. Press–ready Pdfs strip out unnecessary ancillary information. It keeps the information a printer will need for printing a quality piece.
If you get a request for a high resolution Pdf first ask, print–ready or press–ready. Likely they will respond, high resolution. If you’re sending it to a designer, send a press–ready version if it’s to another office (or office like place) send print–ready. Just remember to tell the recipient what version it has been saved.