Susan Bugher said:
Look for a Descreen option in your Epson scanner settings. Wayne Fulton
(as usual) explains all (except why the image looks better in PSP) -
start here:
http://www.scantips.com/basics06.html
Susan, Morten:
Thanks both, now understood. At 100%, both do indeed look
identical, as shown here:
http://www.terrypin.dial.pipex.com/Images/Screenshot100IrfanView.jpg
http://www.terrypin.dial.pipex.com/Images/Screenshot100PSP8.jpg
(Note: When I view these links initially in my Firefox browser, I see
patterning, which disappears when I click to zoom. In MSIE6, it comes
up at full size straightaway.)
Also, here's the original (1MB):
http://www.terrypin.dial.pipex.com/Images/Original-240.jpg
BTW, after scanning, I naturally want to view the *entire* picture, so
that I can see it's properly cropped, what I intended, worth keeping,
etc, etc.
Eventually found a 'Descreening' option in Epson Scan. On a brief try,
happily it does seem to work. And, unlike using the Auto Mode, I can
now preview and scan only the selected section, which of course avoids
later cropping and saves time.
But I'm still keen to understand what exactly I should be looking at
to *know* whether the patterning has been removed! IOW, what
definitive steps should I take directly after scanning and saving a
JPG to know whether or not I need to repeat it with different
settings, or process it further with blurring, smoothing, or resizing?
I don't want to find at some much later stage (such as when I've used
the JPG in a DVD slide show), that the patterns are still present.
Until this discussion here and elsewhere, I'd never realised there was
an issue. But I now see that different image programs can display the
identical file markedly differently. Furthermore, any *one* of the
programs can display differently depending on factors such as zoom
level or window size.
If I'd had JPG associated by default with PaintShop Pro 8 instead of
IrfanView, I'd never have *seen* the patterns when I did my routine
post-scan view. So I could have done all of them and remained
innocently unaware of a potential problem.
So...would the following make sense as a 'definitive test':
Use IrfanView, because limited experience seems to imply it's the most
sensitive at seeing these patterns. Open the JPG full screen and zoom
in and out across a wide range. If no patterns are seen at any level,
then there *are* none.
I also posted in a couple of other newsgroups, and had some very
helpful replies. Here's two:
From Dave Martindale, in alt.comp.periphs.scanners & rec.photo.digital
-----------------------------------------------------------------------
It looks like IrfanView is using nearest-neighbour resampling to bring
the image to 50% of original size. This will generate aliasing
artifacts, and exaggerate any that are already present. PSP is
obviously doing some low-pass filtering with its downsampling and thus
reducing the moire effects.
However, Irfanview is capable of doing very good quality downsampling
if you ask it to. First go to the Properties dialog and select the
"Fullscreen" tab. Find the option that says "Use Resample function
for display options". This tells IV to use its slower but higher
quality resampling for image display instead of nearest neighbour. And
yes, it applies to windowed-mode display as well as fullscreen,
despite where the option is located in the menus.
Then, with an image loaded, do Image->Resize/Resample, pick some
arbitrary new size, make sure the "Resample" box is checked rather
than "Resize", and select one of the resampling filters. Lanczos is
the most expensive, but does the best job of retaining image detail
that can be retained while avoiding creating new aliasing artifacts.
On the other hand, the other filters smooth the image somewhat more
and might be better in this case.
Once you've done this, you should see your display image improved at
any size below 100%. It's unfortunate that Irfanview doesn't provide
a more straightforward way of setting the filter to be used when
viewing.
From Wayne
----------
You always want to judge images ONLY at 100% actual size on the
monitor screen (even if you must scroll around on it). If you scanned
at 600 dpi, it is a huge image, but I think you will see that pattern
is false and not actually present in the image when you view it at
100% actual size. (IrfanView menu View - Actual Size).
Viewing programs only do a quick and dirty (nearest neighbor) resample
to make large images smaller to fit the screen window (fast and
immediate, but relatively poor quality), and it is not unusual to see
moire effects on the video screen, from even real photos, but
especially from the dot patterns in scanned printed images. Photo
editors do this in different ways, some a little better than others,
but none are the same result as actually viewing the actual real
pixels, which are seen only when at 100% actual size.
If this smaller size is what you want to view on the screen, then use
the resample menu to make a smaller copy that is the right size for
viewing. That resample menu is slower, not quite immediate, but wont
create that false pattern, because it uses better (slower) resampling
methods.
====================
(don't have any additional advice). Thanks