From: Richard Ross <rhdesign@xxxxxxxxxxxxx>
Acer quoted:
>>>>640x480 pixels at 72 dpi<<<
...
Now here's my question: I've often seen this business of 72dpi as being the
same as screen resolution and therefore the optimum for scans to be
displayed on monitors. But, ... surely an image scanned at that
resolution will not necessarily be *displayed* at that - it will depend on
the relationship between the dpi of the screen and the video card settings.
Won't it? Or am *I* missing something?
A scale factor, such as 72 DPI, is essentially meaningless with
respect to image data. It's information that may be added to the
header of an image file as a "hint" or indication of the original or
intended scale, such as if it came from a scanner or is going to a
printer, but those devices can have their own ideas of how to
interpret the data.
Output devices generally interpret an image based upon their
intrinsic scale and the actual number of pixels. So if you send a
640x480 "72 DPI" image to a 600 dpi laser printer, you'll get a tiny
image a bit over an inch wide, unless some other software (such as a
printer driver) decides to interpret whatever scale factor may be
embedded in the image. (Graphics professionals generally consider
such interpretation a bug. :-)
So think of "DPI" (or "SPI" for scanners -- samples per inch) as a
characteristic of a media or process, NOT a characteristic of the
image data.
: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229
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