Wide PNG's displaying only coloured stripes?

[David Bovill]

There are lots of time when you need to make these calculations - due
usually to information or interfaces provided by other software (often
defined primarily for print) - in my case I need to pass inches to the
shell and therefore convert to inches from the rect in Rev,

So the question is exactly what is involved in moving from lets say
640 x 480 image rect to a value in inches that you must supply to a
piece of print orientated software? At one time I thought it was just
72 dpi = an inche - but then I never got straight the use of points
and pixels and "dots" per inch. I know what dpi are in print world - I
know (I think) what pixels are in the "screen" world. That is i think
I do :)

    - Pixels are little glowing spots on your screen

    - Dots are little non-glowing spots of colour (usually on paper)

    - the rect and loc etc in Rev refer to pixels of glowing colour

    - inches and other conventional measure refer to fixed distances
in space (relativity not withstanding)

   - to get from pixels or dots to some real physical measure you need
to know the number of pixels or dots per unit of space on the output
device concerned (paper or screen)

    - dpi is this factor and the dpi of monitor screens used to be
72dpi I think all though tis should really be pdi for pixels per inch
or gdpi for glowing dots per inch. 96 is another  number entirely.

Can someone help me here - I think I am in the wrong tree - how do I
know the dpi factor to use in a conversion?