re: PPI VS DPI
Well, you did ask. As for my view, I would suggest starting here:
The First Fundamental Concept about Printers and Video Screens
(That page starts higher, I point to this lower box)
Everyone knows and always knew, that printers print ink drops, perhaps in a screen pattern, at a resolution called dpi, which actually means ink drops per inch.
And we know that image resolution specifies to print pixels per inch (on paper, where inches exist)
This is a given. There can be no alternatives.
However, in commercial prepress, image resolution was historically always called dpi, forever back. That was just the formal name of it, without exception. OK, maybe it was jargon, but that was the formal use, in all the literature, and it was the name, and dpi was always was the use.
Both printer or image terms of dots are only a vague and meaningless term, but both are called dots per inch. A pixel is the color of a (hypothetical) area of paper, and an ink drop is a physical ink drop. Both are called dots, which again, has no specific meaning, until we say what it means. Context always makes it clear. If about images, it is pixels. If about printers, it is ink drops.
Maybe it is like the the editor term Resize. Resize has no meaning, it might be cropping or resampling or scaling, all extremely different, but we sometimes tend to say resize, which is totally meaningless until we say what we mean.
But maybe 15 years ago, inexpensive scanners started appearing, which meant novices with no experience started getting involved, because they had a few hundred dollars and a computer. Then digital cameras seriously started maybe 10 years ago, which brought in the masses, users who could not even imagine a pixel, which are indeed a drastic new notion, unknown until we learn.
So, trying to explain that 2400 dpi printers meant ink drops, and printing at 300 dpi meant pixels, tended to confuse the newbies - the actual problem was that they could not even imagine a pixel. Even though the term dpi had always meant resolution of image pixels, someone got the bright notion that dpi should only be used for printer ink drops, and ppi had to be used for image pixels. Only problem, not all got the word, or even agreed. It was just somebodies notions. Old timers were very comfortable with dpi meaning both. And newbies still saw both terms in use. The self-proclaimed purist people, standing up shouting "No Not DPI" just confused everything that the newbie saw to read, which was no help at all - because dpi actually does exist, plentifully.
My own view is that we obviously must understand the real world, where some say dpi and some say ppi, for the same thing, image resolution. We can say which ever we please, but regardless of our preference, we absolutely must understand it either way. Which is technically trivial, the context makes it clear: if it is about an image, it means pixels. If it is about a printer device, it means ink drops. Many English words have multiple meanings. How many can you think for the word "set", for example. My big dictionary has 116, more than two long columns. Just how it is. We manage. Context tells us the meaning.
So, when someone wants to tell me I can't say dpi, I have to ask "and just who are you that proclaims this?"
If that happens to be you, then check out the formal specifications for JPG and TIF images
http://www.w3.org/Graphics/JPEG/jfif3.pdf (page 5)
http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf (page 38)
These are prestigious organizations, and the formal specifications for these image files CLEARLY SAY DPI. The term ppi is not in those documents. Probably because that idiot had not stood up yet.
But of course, there are no ink drops in image files, there is no possible way to confuse it. But of course, the FORMAL specification for JPG files says DPI. And who are you to say otherwise?
Just teasing, but you see my point?
Every scanner made has specs in dpi (yet they create pixels in images, not ink drops)
I think those people know what they are doing too.
Dye-sub printers, and chemical printers (like at the photo printing places) are continuous tone, they actually mix and print colored pixels instead of ink drops of 3 or 4 colors of ink. Their specs say dpi too.
But some people do say ppi, which is fine with me if they do. I understand it either way, and we all should, since that is what we will hear everywhere.
We know the term 72 dpi is NEVER about ink drops. It would be absurd as ink drops.
Yet search Google (with the quotes):
"72 ppi" Less than 1 million hits.
"72 dpi" 52 million hits (this certainly seems to be current usage)
Just how it is. We have to understand it either way.
Be that as it may, images for monitors and the web could not care less about dpi or ppi. Video devices show pixels directly, one for one. It simply cannot matter what the dpi field in JPG might specify, which is only about printing on paper, not about video devices.
So, the 72 ppi use here does seem rather quaint.
