Barton Bosch <[EMAIL PROTECTED]> writes:

> While we're on the topic of scaling/resampling maybe someone could
> clarify something for me.  I read somewhere that when scaling an image
> for display on a monitor that it was best to change the dpi by the
> same ratio to avoid interpolation.  Elsewhere I have gotten the
> impression that dpi was totally and always irrelevant to images on the
> screen.
> My limited understanding is that when scaling an image from, e.g. 1600
> pixels wide to 400 pixels wide, that it is best to change dpi in the
> same ratio, say, from 72 dpi to 288 dpi.  And further that it is even
> more important when upsampling an image.  The desired result being the
> avoidance of any blurring from the software not being able to map the
> scaled image pixel for pixel.

Unless you disable "Dot-for-Dot" in the GIMP's image window (it's in
the View menu), you will always see one pixel of the image taking up
one pixel on screen (of course only in 1:1 zoom ratio). The dpi
setting is irrelevant for the image display. It becomes of importance
if you want to use the rulers or the measure tool with real-world
units. Then GIMP needs to know how large a pixel will end up on the
final print or projection or whatever your final media is.

Changing the dpi setting alone won't alter your pixel data. It's just
some meta information. Even if you disable dot-for-dot view in GIMP,
the dpi information is only used in the display routines. Your pixel
data is not changed.

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