Moiré interference patterns

Discussion in 'Digital Photography' started by Terry Pinnell, Nov 30, 2005.

  1. First time I've come across this effect. Scanning a calendar, I get
    gross 'interference patterns'. Understand they're more correctly
    called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    2480 doesn't seem to have any setting to remove them at source.
    (Gather some scanners have a 'de-screening' facility to do this.)

    What is best way to handle this please? Is it a matter of scanning at
    say 600 dpi and then using an image editor to reduce the size?

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Nov 30, 2005
    #1
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  2. Re: =?ISO-8859-1?Q?Moir=E9_interference_?==?ISO-8859-1?Q?patterns?=

    On Wed, 30 Nov 2005 17:33:10 +0000, Terry Pinnell wrote:

    >First time I've come across this effect. Scanning a calendar, I get
    >gross 'interference patterns'. Understand they're more correctly
    >called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    >2480 doesn't seem to have any setting to remove them at source.
    >(Gather some scanners have a 'de-screening' facility to do this.)
    >
    >What is best way to handle this please? Is it a matter of scanning at
    >say 600 dpi and then using an image editor to reduce the size?


    Terry,

    filters exist that take the mathematical approach to remove
    moiré patterns entirely. The last time I encountered such a
    filter was when I still used a program called Picture Publisher
    by Micrografx. This program had an excellent moiré filter which
    used clever mathematics to obtain a precise model of the moiré
    pattern and deducted it perfectly without losing any visible
    sharpness.

    Unfortunately I haven't seen anything like it ever since, and I
    had to drop Picture Publisher because of its excessive number of
    defects.

    The moiré filter in Paint Shop Pro is a joke in comparison. It
    is only a soft filter that essentially doesn't remove the moiré
    at all, it just reduces it along with any other high frequencies
    by applying a low pass filter, making the whole picture soft.

    I would also like to know a third-party tool that does what
    Picture Publisher did.

    Hans-Georg

    --
    No mail, please.
     
    Hans-Georg Michna, Nov 30, 2005
    #2
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  3. Terry Pinnell

    Marvin Guest

    Re: =?ISO-8859-1?Q?Moir=E9_interference_patterns?=

    Terry Pinnell wrote:
    > First time I've come across this effect. Scanning a calendar, I get
    > gross 'interference patterns'. Understand they're more correctly
    > called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    > 2480 doesn't seem to have any setting to remove them at source.
    > (Gather some scanners have a 'de-screening' facility to do this.)
    >
    > What is best way to handle this please? Is it a matter of scanning at
    > say 600 dpi and then using an image editor to reduce the size?
    >

    Turning the picture at a slight angle when scanning can reduce the problem.
     
    Marvin, Nov 30, 2005
    #3
  4. Terry Pinnell

    kctan Guest

    calendar scanning should not get moiré pattern. I think it should be the
    screen dots pattern which can be removed by de-screen in your Epson scanner
    advance setting menu.

    "Terry Pinnell" <> wrote in message
    news:...
    > First time I've come across this effect. Scanning a calendar, I get
    > gross 'interference patterns'. Understand they're more correctly
    > called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    > 2480 doesn't seem to have any setting to remove them at source.
    > (Gather some scanners have a 'de-screening' facility to do this.)
    >
    > What is best way to handle this please? Is it a matter of scanning at
    > say 600 dpi and then using an image editor to reduce the size?
    >
    > --
    > Terry, West Sussex, UK
     
    kctan, Nov 30, 2005
    #4
  5. "kctan" <> wrote:

    >calendar scanning should not get moiré pattern. I think it should be the
    >screen dots pattern which can be removed by de-screen in your Epson scanner
    >advance setting menu.


    Is there such a feature? If so, as I said, so far I haven't found it.
    Could you tell me exactly where it is please?

    See also my other replies, re apparent difference between viewers.

    BTW, why do you say "Calendar scanning should not get moiré pattern"?

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Nov 30, 2005
    #5
  6. Terry Pinnell

    Wayne Guest

    Re: =?ISO-8859-1?Q?Moir=E9?= interference patterns

    In article <>,
    says...
    >
    >
    >First time I've come across this effect. Scanning a calendar, I get
    >gross 'interference patterns'. Understand they're more correctly
    >called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    >2480 doesn't seem to have any setting to remove them at source.
    >(Gather some scanners have a 'de-screening' facility to do this.)
    >
    >What is best way to handle this please? Is it a matter of scanning at
    >say 600 dpi and then using an image editor to reduce the size?



    Yes. Scan images in printed material at least at 300 dpi, and at 600
    dpi if you can stand it (if the image is small enough it is bearable).
    Moire is digital aliasing, caused by scanning resolution insufficient
    to resolve the detail. The dots are the detail, and the dots are
    typically (often) 150 dpi, which therefore theoretically requires at
    least 300 dpi to resolve them (Nyquist). 600 dpi is better.

    There are other workarounds, but the best solution is to increase the
    scanning resolution, and then resample it to any smaller desired size.

    --
    Wayne
    http://www.scantips.com "A few scanning tips"
     
    Wayne, Nov 30, 2005
    #6
  7. Hans-Georg Michna <> wrote:

    >On Wed, 30 Nov 2005 17:33:10 +0000, Terry Pinnell wrote:
    >
    >>First time I've come across this effect. Scanning a calendar, I get
    >>gross 'interference patterns'. Understand they're more correctly
    >>called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    >>2480 doesn't seem to have any setting to remove them at source.
    >>(Gather some scanners have a 'de-screening' facility to do this.)
    >>
    >>What is best way to handle this please? Is it a matter of scanning at
    >>say 600 dpi and then using an image editor to reduce the size?

    >
    >Terry,
    >
    >filters exist that take the mathematical approach to remove
    >moiré patterns entirely. The last time I encountered such a
    >filter was when I still used a program called Picture Publisher
    >by Micrografx. This program had an excellent moiré filter which
    >used clever mathematics to obtain a precise model of the moiré
    >pattern and deducted it perfectly without losing any visible
    >sharpness.
    >
    >Unfortunately I haven't seen anything like it ever since, and I
    >had to drop Picture Publisher because of its excessive number of
    >defects.
    >
    >The moiré filter in Paint Shop Pro is a joke in comparison. It
    >is only a soft filter that essentially doesn't remove the moiré
    >at all, it just reduces it along with any other high frequencies
    >by applying a low pass filter, making the whole picture soft.
    >
    >I would also like to know a third-party tool that does what
    >Picture Publisher did.
    >

    Thanks Hans-Georg.

    Since my post, I've discovered something very puzzling. By default, I
    was viewing the finished JPG scan in IrfanView. That showed the bad
    patterns. And they remained with various DPI changes in Epson Scan
    (300, 400, 600, 150, 96). But I happened to open one in PaintShop Pro
    8 (in order to see what filters I might use), and the patterns were
    gone! This is with both programs filling the screen with the image to
    about the same size.

    I also found something else that I haven't figured out. Those first
    scans were done by opening Epson Scan direct and using its
    Professional Mode. But just now I instead tried opening Smart Panel
    and then selecting Scan & Save. That doesn't present any options, it
    just appears to scan using Fully Auto mode (and takes a fair while,
    presumably because it's scanning the entire area, because there's no
    Preview allowing cropping). But the resulting JPG was not patterned!

    Any help getting my mind around these would be appreciated please.

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Nov 30, 2005
    #7
  8. Marvin <> wrote:

    >Terry Pinnell wrote:
    >> First time I've come across this effect. Scanning a calendar, I get
    >> gross 'interference patterns'. Understand they're more correctly
    >> called Moiré patterns. I'm disappointed that my Epson Perfection (!)
    >> 2480 doesn't seem to have any setting to remove them at source.
    >> (Gather some scanners have a 'de-screening' facility to do this.)
    >>
    >> What is best way to handle this please? Is it a matter of scanning at
    >> say 600 dpi and then using an image editor to reduce the size?
    >>

    >Turning the picture at a slight angle when scanning can reduce the problem.


    Thanks, I'll experiment with that when I get these other puzzles
    sorted!

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Nov 30, 2005
    #8
  9. Wayne <> wrote:

    >In article <>,
    > says...


    >>What is best way to handle this please? Is it a matter of scanning at
    >>say 600 dpi and then using an image editor to reduce the size?



    >Yes. Scan images in printed material at least at 300 dpi, and at 600
    >dpi if you can stand it (if the image is small enough it is bearable).
    >Moire is digital aliasing, caused by scanning resolution insufficient
    >to resolve the detail. The dots are the detail, and the dots are
    >typically (often) 150 dpi, which therefore theoretically requires at
    >least 300 dpi to resolve them (Nyquist). 600 dpi is better.
    >
    >There are other workarounds, but the best solution is to increase the
    >scanning resolution, and then resample it to any smaller desired size.


    Thanks Wayne. Just tried one (a photo of about 5" x 8") at 600 dpi
    then halved its size in IrfanView and it did indeed make a big
    improvement. But please see my reply to Hans-Georg. I'm now confused
    as to whether this patterning is *real*, or just a flaw in my usually
    excellent IrfanView.

    Here are a couple of screen shots showing the comparison. Both scans
    were at 240 dpi. I then used Print Scrn to capture both and paste as a
    new image in PSP 8. As you see, the view in IrfanView shows the
    patterns, but PSP 8 does not (or vet much diminished).

    http://www.terrypin.dial.pipex.com/Images/Screenshot240-IrfanView.jpg
    http://www.terrypin.dial.pipex.com/Images/Screenshot240-PSP.jpg

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Nov 30, 2005
    #9
  10. Terry Pinnell

    Wayne Guest

    Re: =?ISO-8859-1?Q?Moir=E9?= interference patterns

    In article <>,
    says...
    >
    >Thanks Wayne. Just tried one (a photo of about 5" x 8") at 600 dpi
    >then halved its size in IrfanView and it did indeed make a big
    >improvement. But please see my reply to Hans-Georg. I'm now confused
    >as to whether this patterning is *real*, or just a flaw in my usually
    >excellent IrfanView.
    >
    >Here are a couple of screen shots showing the comparison. Both scans
    >were at 240 dpi. I then used Print Scrn to capture both and paste as a
    >new image in PSP 8. As you see, the view in IrfanView shows the
    >patterns, but PSP 8 does not (or vet much diminished).
    >
    >http://www.terrypin.dial.pipex.com/Images/Screenshot240-IrfanView.jpg
    >http://www.terrypin.dial.pipex.com/Images/Screenshot240-PSP.jpg



    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.

    --
    Wayne
    http://www.scantips.com "A few scanning tips"
     
    Wayne, Nov 30, 2005
    #10
  11. Terry Pinnell

    kctan Guest

    Moiré only happens in subject with very fine surface's textures like textile
    or mesh's fabric or net. It happens on photography work only. Calendar
    images are press printing on smooth paper surface that will never produce
    moiré pattern. Even it does, it is from the printing screens not properly in
    control that reproduces as moiré image and not pattern.

    "Terry Pinnell" <> wrote in message
    news:...
    > "kctan" <> wrote:
    >
    >>calendar scanning should not get moiré pattern. I think it should be the
    >>screen dots pattern which can be removed by de-screen in your Epson
    >>scanner
    >>advance setting menu.

    >
    > Is there such a feature? If so, as I said, so far I haven't found it.
    > Could you tell me exactly where it is please?
    >
    > See also my other replies, re apparent difference between viewers.
    >
    > BTW, why do you say "Calendar scanning should not get moiré pattern"?
    >
    > --
    > Terry, West Sussex, UK
     
    kctan, Nov 30, 2005
    #11
  12. Terry Pinnell

    kctan Guest

    "Terry Pinnell" <> wrote in message
    news:...

    > Is there such a feature? If so, as I said, so far I haven't found it.
    > Could you tell me exactly where it is please?
    >
    > Terry, West Sussex, UK


    I can't tell it but mine got to be selected during the time that scanner
    starts, from the splash screen, click the advance tab to go into advance
    mode. There are plenty of manipulations there.
     
    kctan, Nov 30, 2005
    #12
  13. On Wed, 30 Nov 2005 19:25:12 +0000, in rec.photo.digital Terry Pinnell
    <> wrote:

    >Since my post, I've discovered something very puzzling. By default, I
    >was viewing the finished JPG scan in IrfanView. That showed the bad
    >patterns. And they remained with various DPI changes in Epson Scan
    >(300, 400, 600, 150, 96). But I happened to open one in PaintShop Pro
    >8 (in order to see what filters I might use), and the patterns were
    >gone! This is with both programs filling the screen with the image to
    >about the same size.


    Probably different resampling/display algorithms.

    --
    Ed Ruf Lifetime AMA# 344007 ()
    See images taken with my CP-990/5700 & D70 at
    http://edwardgruf.com/Digital_Photography/General/index.html
     
    Ed Ruf (REPLY to E-MAIL IN SIG!), Dec 1, 2005
    #13
  14. Terry Pinnell

    Frank ess Guest

    =?iso-8859-1?Q?Re:_Moir=E9_interference_patterns?=

    Terry Pinnell wrote:
    > Hans-Georg Michna <> wrote:
    >
    >> On Wed, 30 Nov 2005 17:33:10 +0000, Terry Pinnell wrote:
    >>
    >>> First time I've come across this effect. Scanning a calendar, I
    >>> get
    >>> gross 'interference patterns'. Understand they're more correctly
    >>> called Moiré patterns. I'm disappointed that my Epson Perfection
    >>> (!)
    >>> 2480 doesn't seem to have any setting to remove them at source.
    >>> (Gather some scanners have a 'de-screening' facility to do this.)
    >>>
    >>> What is best way to handle this please? Is it a matter of scanning
    >>> at say 600 dpi and then using an image editor to reduce the size?

    >>
    >> Terry,
    >>
    >> filters exist that take the mathematical approach to remove
    >> moiré patterns entirely. The last time I encountered such a
    >> filter was when I still used a program called Picture Publisher
    >> by Micrografx. This program had an excellent moiré filter which
    >> used clever mathematics to obtain a precise model of the moiré
    >> pattern and deducted it perfectly without losing any visible
    >> sharpness.
    >>
    >> Unfortunately I haven't seen anything like it ever since, and I
    >> had to drop Picture Publisher because of its excessive number of
    >> defects.
    >>
    >> The moiré filter in Paint Shop Pro is a joke in comparison. It
    >> is only a soft filter that essentially doesn't remove the moiré
    >> at all, it just reduces it along with any other high frequencies
    >> by applying a low pass filter, making the whole picture soft.
    >>
    >> I would also like to know a third-party tool that does what
    >> Picture Publisher did.
    >>

    > Thanks Hans-Georg.
    >
    > Since my post, I've discovered something very puzzling. By default,
    > I
    > was viewing the finished JPG scan in IrfanView. That showed the bad
    > patterns. And they remained with various DPI changes in Epson Scan
    > (300, 400, 600, 150, 96). But I happened to open one in PaintShop
    > Pro
    > 8 (in order to see what filters I might use), and the patterns were
    > gone! This is with both programs filling the screen with the image
    > to
    > about the same size.
    >
    > I also found something else that I haven't figured out. Those first
    > scans were done by opening Epson Scan direct and using its
    > Professional Mode. But just now I instead tried opening Smart Panel
    > and then selecting Scan & Save. That doesn't present any options, it
    > just appears to scan using Fully Auto mode (and takes a fair while,
    > presumably because it's scanning the entire area, because there's no
    > Preview allowing cropping). But the resulting JPG was not patterned!
    >
    > Any help getting my mind around these would be appreciated please.


    My Epson Scan software ver. 2.03A offers a descreening filter with
    four Screen Ruling 'level' choices. In professional mode it is near
    the bottom of options offered, just below Unsharp Mask Filter.

    If that doesn't have the desired effect, do a Gaussian Blur sufficient
    to your purposes. On a 3000x2000 ppi image, a blur of something
    between 0.8 and 1.3 seems to eliminate the pattern effect without too
    much of a deleterious effect on detail.
    http://www.fototime.com/02FB5204FA89BE0/orig.jpg (99KB file)

    My guess about the Fully Auto mode is that it applied the Descreening.

    It doesn't require much of an offset or interference to render a
    pattern effect onscreen (anoraks please forgive my unfamiliarity with
    approprate terms of art). When I look at a scanned programme cover in
    Windows' viewer or Photo Shop, rolling the mouse wheel in the view
    resizing function passes through several sizes that are alternately
    pattern-free and patterned in various configurations. Proportion of
    the screen utilized also has an effect.

    --
    Frank ess
     
    Frank ess, Dec 1, 2005
    #14
  15. Terry Pinnell <> writes:

    >Here are a couple of screen shots showing the comparison. Both scans
    >were at 240 dpi. I then used Print Scrn to capture both and paste as a
    >new image in PSP 8. As you see, the view in IrfanView shows the
    >patterns, but PSP 8 does not (or vet much diminished).


    >http://www.terrypin.dial.pipex.com/Images/Screenshot240-IrfanView.jpg
    >http://www.terrypin.dial.pipex.com/Images/Screenshot240-PSP.jpg


    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.

    Dave
     
    Dave Martindale, Dec 1, 2005
    #15
  16. "kctan" <> wrote:

    >Moiré only happens in subject with very fine surface's textures like textile
    >or mesh's fabric or net. It happens on photography work only. Calendar
    >images are press printing on smooth paper surface that will never produce
    >moiré pattern. Even it does, it is from the printing screens not properly in
    >control that reproduces as moiré image and not pattern.


    Well, still not sure I follow the distinction you're making, but
    whatever they're called, I don't want them! FWIW, these patterns
    change as I zoom in or out with IrfanView.

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Dec 1, 2005
    #16
  17. "kctan" <> wrote:

    >"Terry Pinnell" <> wrote in message
    >news:...
    >
    >> Is there such a feature? If so, as I said, so far I haven't found it.
    >> Could you tell me exactly where it is please?
    >>
    >> Terry, West Sussex, UK

    >
    >I can't tell it but mine got to be selected during the time that scanner
    >starts, from the splash screen, click the advance tab to go into advance
    >mode. There are plenty of manipulations there.
    >


    Thanks, have now found the Descreening option (hadn't realised I
    needed to scroll down to get access to all settings).

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Dec 1, 2005
    #17
  18. "Frank ess" <> wrote:

    >My Epson Scan software ver. 2.03A offers a descreening filter with
    >four Screen Ruling 'level' choices. In professional mode it is near
    >the bottom of options offered, just below Unsharp Mask Filter.


    Thanks! Now found it from those directions. I hadn't realised I needed
    to scroll downwards in order to see all my setting options. And I use
    a 1024 x 768 screen, which I don't regard as abnormally small <g>. (I
    also see a Dust Removal option hiding at the bottom.)

    >If that doesn't have the desired effect,do a Gaussian Blur sufficient
    >to your purposes. On a 3000x2000 ppi image, a blur of something
    >between 0.8 and 1.3 seems to eliminate the pattern effect without too
    >much of a deleterious effect on detail.
    >http://www.fototime.com/02FB5204FA89BE0/orig.jpg (99KB file)


    >My guess about the Fully Auto mode is that it applied the Descreening.
    >
    >It doesn't require much of an offset or interference to render a
    >pattern effect onscreen (anoraks please forgive my unfamiliarity with
    >approprate terms of art). When I look at a scanned programme cover in
    >Windows' viewer or Photo Shop, rolling the mouse wheel in the view
    >resizing function passes through several sizes that are alternately
    >pattern-free and patterned in various configurations. Proportion of
    >the screen utilized also has an effect.


    Only tried the Descreening option once so far, but 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, 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.

    Any other suggestions would be appreciated please.

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Dec 1, 2005
    #18
  19. (Dave Martindale) wrote:

    >Terry Pinnell <> writes:
    >
    >>Here are a couple of screen shots showing the comparison. Both scans
    >>were at 240 dpi. I then used Print Scrn to capture both and paste as a
    >>new image in PSP 8. As you see, the view in IrfanView shows the
    >>patterns, but PSP 8 does not (or vet much diminished).

    >
    >>http://www.terrypin.dial.pipex.com/Images/Screenshot240-IrfanView.jpg
    >>http://www.terrypin.dial.pipex.com/Images/Screenshot240-PSP.jpg

    >
    >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.


    Wayne, Dave: Excellent - thanks a lot for those detailed explanations.
    Finally think I have my mind around this.

    Viewed at 100%, both PSP and IV do indeed show identical views, as you
    see here:
    http://www.terrypin.dial.pipex.com/Images/Screenshot100PSP8.jpg
    http://www.terrypin.dial.pipex.com/Images/Screenshot100IrfanView.jpg
    (In my Firefox browser, the initial display of these still shows
    patterns; clicking to zoom gets full-size, and they disappear. In
    MSIE6 they come up OK at once.)

    Also, here's the original (1 MB).
    http://www.terrypin.dial.pipex.com/Images/Original-240.jpg

    I'll experiment with IV's settings later.

    Please also see my reply just now to Frank. I'd appreciate your
    thoughts on my question about a definitive (but fast and simple) test
    please.

    --
    Terry, West Sussex, UK
     
    Terry Pinnell, Dec 1, 2005
    #19
  20. Terry Pinnell <> writes:

    >Viewed at 100%, both PSP and IV do indeed show identical views, as you
    >see here:
    >http://www.terrypin.dial.pipex.com/Images/Screenshot100PSP8.jpg
    >http://www.terrypin.dial.pipex.com/Images/Screenshot100IrfanView.jpg
    >(In my Firefox browser, the initial display of these still shows
    >patterns; clicking to zoom gets full-size, and they disappear. In
    >MSIE6 they come up OK at once.)


    If Firefox is automatically shrinking the image to make it fit the
    window, you're seeing the results of the downsampling algorithm built
    into Firefox, which you have no control over (other than turning it
    off). IE will also downsize automatically, if you selected that option,
    and again you don't have any control over the algorithm used. To avoid
    these uncertainties, view at 100% size.

    By the way, Photoshop is even *more* insidious at doing things behind
    the scenes. If you have the "image cache" enabled (this is in PS6; it
    might be called something else now), Photoshop automatically computes
    smaller-sized versions of large images, and uses them for display when
    you are displaying the image at some sizes below 100%. These sub-sized
    images are properly filtered when created. But at some magnifications,
    Photoshop uses nearest-neighbour resampling to the final size, which
    is what you saw in Irfanview. So as you change magnification in
    Photoshop, moire effects can get better or worse depending on exactly
    what route Photoshop took to create the displayed image at that size.

    For the same reason, film grain (in scanned film images) may appear to
    get worse (compared to 100% view) or better at smaller sizes. Filtered
    downsampling reduces grain, because grain is mostly high-frequency noise
    that is reduced by filtering. Nearest-neighbour downsampling doesn't
    reduce grain noise amplitude, but it makes the grain look bigger (called
    grain aliasing).

    >Please also see my reply just now to Frank. I'd appreciate your
    >thoughts on my question about a definitive (but fast and simple) test
    >please.


    Haven't seen it yet.

    Dave
     
    Dave Martindale, Dec 1, 2005
    #20
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