Neil Gould wrote:

Not really. Pixels per inch (ppi) has no meaning that isn't communicated
equally well as dpi. Both describe an abstraction that has nothing to do
with the image itself, as a digital image only contains a matrix of pixels
that have no size.

Not quite the image itself, no. That only has pixels.

But with the processes of scanning and printing.

A scanner is able to produce only a certain number of pixels per unit of
length or width.
The pixel size of the image is limited/determined by that.
So the PPI of a scanner has indeed something to do with the image. But only
until it is scanned.

A print consists of dots of ink, thrown, or transferred onto a bit of paper.
There too the machinery involved and technique it uses is setting limits to
what the picture it produces can be. It has very much to do with the image
itself.

Whereas a pixel is a pixel, a dot is not a pixel. How much dots make up a
pixel is determined by the print technology.

So PPI and DPI are not (!) interchangeable.


However... the incorrect usage of both terms is already so widespread
that...

On the other hand, we have managed very well to get rid of the silly use of
the word "prime".
I, for one, are hard working trying to irradicate the use of "mirror lock
up" when pre-release is meant. And would you believe it, signs are beginning
to show that people take notice!

So why not try to set this "dpi" thing straight too?
;-)