RE: RE: tifs at 240 dpi worth redoing?

["Combs, Richard" <richard -dot- combs -at- Polycom -dot- com>]

Boudreaux, Madelyn wrote:
 
> Robert Lauriston informed me, as he does:
> >Pixels per inch is no more meaningful than dpi.
> 
> Digital cameras use pixels. They do not use "dots" which is what the D
> in DPI refers to. The dots are related to holes in a printer's screen.

If you're thinking of halftone screens, that's lines per inch (lpi), a
different animal. IIRC, 120 lpi is pretty high resolution printing. 

For all intents and purposes pixels and dots are the same. 

Robert's point is that it makes no sense to tell the photographer "I
want 300 dpi photos." The camera is going to produce files that are X
pixels wide and Y pixels high. 

IIRC, the image sensor in most consumer DSLRs is about half the size of
a 35 mm film frame (which is 24 x 36 mm, or about 1" x 1.5"). So Al's 10
megapixel camera might have 3888 pixels / 0.75", or about 5000 pixels
per inch.

But nobody prints 0.5" x 0.75" in pictures. The ppi/dpi are really
meaningful only _after_ you've decided what the output size of that 3888
x 2592 image will be. If you tell the photographer, "I want 300 dpi
pictures," she ought to reply, "OK, the image contains 3888 horizontal
pixels, so print it 3888/300, or 12.96" wide. If you want a smaller
image, either discard some of the pixels (downsample) or accept a higher
dpi." 


Richard G. Combs
Senior Technical Writer
Polycom, Inc.
richardDOTcombs AT polycomDOTcom
303-223-5111
------
rgcombs AT gmailDOTcom
303-777-0436
------






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