[filmscanners] RE: dpi - formerly PS sharpening

["Austin Franklin" <darkroom@ix.netcom.com>]

> >> 2592x3888 pixels, 2720 dpi, 4x6inch, 22.7MB
> >>
> >> So it *is* saving a resolution in dpi
> >
> >I believe it is simply calculating the DPI.  It's certainly easy
> enough to
> >do...  What file format are you talking about, BTW?
>
> TIFF files.

Hi Ken,

TIFF files can have "resolution" tags (two, one for X and one for Y), so
they probably are saving the resolution(s).  It's a given that they save the
pixel dimensions, or you couldn't reconstruct the xy of the image.  They
also need one of two, either physical dimensions (as in inches)...or PPI
(Pixels Per Inch, mistakenly called DPI by some, or simply called
"resolution"), and either can be derived from the other.

> >When you read the image back into
> >Viewscan (I assume you can do this), does it still have the dpi it was
> >scanned at, even after resizing?
>
> No, it doesn't, it's changed.

OK, that makes sense.  For some reason, I took it that the comment was it
saved the resolution that it was scanned at...which it probably does when
creating the file from the scanner, but, obviously, after resizing, it
changes that.  I don't know any file format that keeps the "scanned at DPI"
information as a separate field...although one could put it in some comment
field or something I guess.

> Interesting, I had never done that -
> re-looked at an image on disk with the scanning software.  I just
> called up an unaltered TIFF.   Why is that?  Would it help if I cited
> the changes?

If you see something that doesn't make sense, and want to try to figure it
out, please do.

Regards,

Austin

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