Digital BW, The Print

John,

Not quite so simple! Your monitor may be set to imitate resolutions from xxx 
to yyy, but it only has one fixed screen pixel 'resolution' - that is the 
spacing of the physical pixels (rgb phosphors on a CRT monitor or of the 
individual lcd elements on a LCD monitor). Any other resolution is just 
fudged, spreading an image pixel across several screen elements or ignoring 
some image pixels. The 72ppi (for Mac monitors) and 96ppi (for PC monitors) 
that are often mentioned were, I think, just a general average of these 
actual screen pixel resolutions in the past.

For example, on my 1600x1200 lcd screen, one image pixel at actual 
resolution in PS, occupies one r,g,and b element horizontally, but two of 
each elements vertically. That is the maximum and optimal resolution for 
this monitor. Each physical element is roughly 1.5 times taller than it is 
wide, so two elements high by three elements wide gives a square image 
pixel. At any other resolution, the image pixels have to be fudged onto the 
actual screen pixels. Just have a look with a x10 hand lens at different 
resolutions.

With CRT monitors it is even stranger, since the phosphor dots are arranged 
in triangular arrays with varying dot pitches (leaving out the 
trinitron-type monitors).

The clearest picture on the screen is usually achieved when the image 
resolution and size equal the real screen resolution and size, whether 72, 
96ppi, or whatever.

Bob Frost.

----- Original Message ----- 
From: "John Houghton" <j.houghton@...>




> >I thought the resolution on monitors is either 72 ppi or 75 ppi,

It is unrealistic to make any such assumptions.  My monitor can be
set to resolutions in the range 800x600 to 1920x1440.  Which one you
choose is down to personal taste, viewing distance, and how good your
eyesight is.  The ppi resolution value embedded in the image is
usually ignored by the browser.  All that needs to be understood is
that pixels in the image are displayed in individual pixels on the
screen.  So if the screen resolution is 800 pixels wide, an image
that is 400 pixels wide will fill half the width of the screen.  It's
that simple.