[filmscanners] Re: PS sharpening

["Maris V. Lidaka Sr." <mlidaka@ameritech.net>]

Brian said the file size was reduced, so there was apparently resampliing
(downsampling).  Your hypothetical of entering 11 inches in the new
dimension, with the resampling box checked or unchecked, would not result in
PS computing 11 inches x 4000 ppi.  PS would reduce the ppi proportionately
in either case.

Try it.

Maris

----- Original Message -----
From: "Anthony Atkielski" <anthony@atkielski.com>
To: <mlidaka@Ameritech.Net>
Sent: Friday, August 09, 2002 2:32 AM
Subject: [filmscanners] Re: PS sharpening


Brian writes:

> If I scan a 35 mm slide or negative at 4000
> dpi in a Nikon Coolscan 4000 and I want to make
> a print in Photoshop, I alter the long dimension
> to 11 inches (the short dimension ends up at
> whatever to retain the proper dimensions).
> Since this usually ends up in a file size that is
> smaller than what it was originally, does this
> mean the image will be downsampled?

No.  By default, when you enter a dimension in the Image Size dialog box,
Photoshop will resample the image to match the dimensions you've given.  In
the case of pixels, PS simply resamples up or down to match the new pixel
dimensions.  In the case of a physical dimension like 11 inches (entered in
the "Print Size" portion of the dialog), however, PS resamples up or down to
match the new physical dimension _after_ calculating the number of pixels
required by multiplying the physical dimension by the number of pixels per
inch.  When you open a scan from the Coolscan, the ppi is set to 4000 (the
scanner's resolution); and the number of pixels in the image corresponds to
the number of pixels in a 35mm frame scanned at 4000 ppi, or about 5669x3779
pixels.  If you now enter just 11 inches as the new dimension in the
resizing dialog, Photoshop will compute 11 inches x 4000 ppi = 44000 pixels,
and will upsample the image to this size.  In general, this is not what you
want.

[remainder snipped]


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