[filmscanners] RE: Postprocessing - Resizing for screen display

["Laurie Solomon" <laurie@advancenet.net>]

I have been staying quite and following the thread and holding my tongue
to see what others might suggest.  However, it appears that everyone has
neglected the questions dealing with resizing and focused on sharpening.
So I guess I have to jump in and ask the difficult primary questions.

First, what do you mean by "resizing" and how are you doing this
"resizing?"  By "resizing." are you referring to changing the resolution
via interpolation methods or keeping the actual original resolutions
while increasing or decreasing the lineal dimensions of the image?

Second, are you increasing the resolution form the original resolution
and from what to what; or are you decreasing the original resolution and
from what to what?

Third, if you are increasing or decreasing the original lineal
dimensions from the original dimensions without changing the original
actual resolutions, how are you doing this - by what method in what
program?

If you are merely changing the lineal dimensions of the image to a new
size (namely, scaling the image) without making changes to the actual
original resolutions of the image, you will be changing the effective
resolution.  Increasing the size will result in an effective
proportional decrease in the resolution, while decreasing the image
scale will result in an effective proportional increase in the
resolution.  This change in resolution may not be readily known since
the effective ppi will change but the actual total number of pixels may
not change; they are either just more concentrated or spread out. Should
the effective ppi be reduced to 100 ppi or less, the quality and
sharpness of the display will be effected, becoming softer in nature and
involving fewer pixels to sharpen.  Thus, one may need to take this into
account when choosing and applying sharpening methods.  Most sharpening
methods rely on hard straight edges so that nature of the image in
question as well as the amount of resolution that it has will impact on
the quality of one's sharpening results.

If one is engaging in actually changing the resolutions by means of
interpolation, then one needs to be aware that different interpolation
methods may effect the quality of the image. However, here again,
resolutions of 100 ppi or less along with the nature of the image in
question will limit the degree of quality sharpening that one can do.

Having said that, the issue of sharpening per se can be addressed more
accurately.  If you are comparing the sharpness of the image on the
monitor versus the sharpness of the image when printed on paper, you may
find a natural discrepancy between them since the brightness and
contrast of the monitor as well as the nature of the type of monitor
display will bear on the apparent sharpness that one sees.  This also
will be effected by the nature of the image along with the low
resolutions of most screen displays as compared to their printed
versions.

Among the various techniques of sharpening other than single-step global
sharpening are incremental global sharpening, single-step local
sharpening, and incremental local sharpening.  All sharpening should be
done while viewing a preview display set at 100% of various locations in
the overall image in the case of global sharpening or of various
locations in the area being sharpened in the case of local sharpening.
One can use any one of a variety of sharpening methods (i.e., USM, edge
sharpening, LAB Color sharpening, Pixel Genius' Photokit Sharpener, or
the like) when employing any of the above mentioned techniques.

Typically with USM method, one uses a low threshold of 1-2 and small
radius of 1-3 with the actual numbers depending on the type of image.
The amount of sharpening depends on how the image appears and on the
nature and type of image in question.

----Original Message----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk] On Behalf Of
Al@greenspace.freeserve.co.uk
Sent: Wednesday, February 15, 2006 8:16 AM
To: laurie@advancenet.net
Subject: [filmscanners] Postprocessing - Resizing for screen display

> I know this has been asked before so my apologies for going over old
> ground!
>
> When I scan my wife's slides, she normally likes a resized
> version for use as desktop wallpaper.  My problem is that,
> after I resize the images in Photoshop, they either don't
> look sharp enough or I manage to oversharpen them and make
> them look unnatural.  I have tried both USM and the high-pass
> filter but just can't get it looking right!  The originals
> are detailed enough - its just my poor technique.  (I'm no
> better at resizing my digicam images for the screen.)
>
> What techniques do list members use to resize/sharpen screen
> display images and what USM etc values seem best?  I'm
> determined to produce an image which my wife actually feels
> does the original justice........
>
>
> TIA,
>
>
> Al
>
>
>
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