Re: filmscanners: Film Scanner Question Again

[rafeb <rafeb@channel1.com>]

At 01:56 AM 7/8/01 EDT, Roger Miller wrote:

<snip>

Roger, there were a couple of points in your recent 
post to Rick Decker that I'd like to comment on.

My experience with the 1640 SU is that there is 
absolutely no advantage to setting 3200 dpi 
resolution (as compared to 1600.)  There are a 
number of scanners out there with "assymetrical" 
resolutions, and it's usually a shell game.  
Ditto for printer resolutions.  The number 
that matters is the lower one.  The higher 
number is simply for ad copy.  "Looks good on 
the side of the box" -- as the marketing guys 
say.

The other is the matter of resizing/resampling 
the image in Photoshop.  You (and Rick) should 
understand the difference.

In Photoshop's Image->Image Size dialog, there's 
a check-box labeled "Resample Image."

If you CHECK this box, PS will either "create" or 
throw away pixels according to the resolution, 
height, and width that you ask for, and the 
resolution, height and width of the existing 
image.

If you UN-CHECK this box, PS will neither create 
nor destroy pixels; it merely changes and internal 
tag, somewhere in the image file, that determines 
the physical size of the printed image.

If you scanned a 35 mm frame on the 1640SU, you 
get a file that's 1600 x 2400 pixels (let's use 
round numbers here.)  If you set target size at 
100% in the scanner driver (I'm working from 
memory here) it will arrive in Photoshop sized 
at 1" x 1.5". If you print it that way, you'll 
get a 1" x 1.5" print.

So you want to resize or resample.  Which to 
choose?  Fortunately in Photoshop, it doesn't 
matter much -- Photoshop does a good job 
resampling.  But just bear in mind -- with 
"Resampling" an entirely new image is created, 
pixel by pixel.  With "Resize" the original 
pixels in the image remain untouched.  (So 
"Resize" happens almost instantaneously, 
whereas "Resample" takes some time, maybe 
15-30 seconds on this image, on a reasonably 
fast machine.)

A "Resize" of this 1600 x 2400 image might 
yield, for example:

-- an image 2" x 3" at 800 dpi
-- an image 4" x 6" at 400 dpi
-- an image 8" x 12" at 200 dpi

and so on.

"Resize" is probably more of a purist's 
approach.  There's no possibility of degrading 
the image in any way.

"Resample" will either create new pixels (by 
interpolation) or throw them away (by averaging 
and decimation.)  With "Resample" an entirely 
new image is created for you.

Finally... bear in mind that the scanner's 
rated dpi has almost nothing to do with sharpness.
I can prove to you easily that the 1640's 
so-called "1600 dpi" yields an image much less 
sharp than a Polaroid SprintScan Plus working 
at 1350 dpi -- half its rated resolution.



rafe b.