Why not do moire filtration in post-process?

Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?

I suppose that you don't want to force users to post-process images.

Toby

"Rich" wrote in message
oups.com...
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?

"Rich" wrote in message
oups.com...
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?



This was talked about back when the K10D started to have sample shots
posted. Some of the sample shots had moiré in them. There really isn't any
way to get rid of it post process. If your camera has it it is the fault of
the camera. Some are more susceptible than others because the filter
(hardware) that gets rid of it or reduces it is better than others. The
Leica M8 has some major problems.

Once the moiré pattern is in the image the only way to get rid of it is to
blur the image and that isn't something people want.

=(8)

On Jun 12, 9:58 pm, Rich wrote:
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?


Kodak DCS SLRs were extremly sharp, but had a lot of problems with
moire. There was a program, photo or picture mechanic that Kodak
absorbed into Photo Desk, the Kodak RAW program. Moire went away with
heavier AA filters, cutting back on over all sharpness. I worked in a
studio from 1998 to 2004, they used Kodak DCS 460s and 760s, always
had to process for moire. But they rented a D1X when one camera was
down, he rejected every pic from the D1X for not being sharp enough,
though he was using his own lenses.

Tom

On Jun 13, 3:58 am, Rich wrote:
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?


It's not possible. Look, for example, at
http://cnx.org/content/m0050/latest/
in particular fig. 2. The top part is the frequency spectrum of the
actual signal; if you record it with insufficient sampling rate (ie
number of pixels per mm), you get the thing in the middle, while if
you have high enough sampling point density you get the bottom signal
(all in frequency space). As you can see, from the bottom signal you
can recontstruc the original with no problem, but from the middle on
you can't: some high-frequency information has been lost due to
overlapping images of the real frequency spectrum.

Now if you don't have enough sampling points to avoid aliasing, the
only solution is to remove the high frequencies from the signal (ie to
low pass filter it), which is what most cameras do. In other words,
you blur the image. There is always a tradeoff between blurring too
much and having artifacts; whole papers have been written on how to
optimize this tradeoff for various definitions of better.

Anyway, the short answer is you can't avoid either aliasing or
blurring. What you can do (in cameras with bayer sensors) is
automatically recognise aliasing artifacts and desaturate the colour
there, making them much less visible. I have no idea if this is done
by any camera (or raw converter) automatically.

But low-pass filtering with most current cameras certainly looks much
more natural to me. Opinions of course differ.

And lo, Rich emerged from the ether
and spake thus:
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?

It's definitely possible. MaxMax, the somewhat venerable service
company known for IR conversions, offers what they call "HotRod"
service, which involves removing the anti-moire filter from your
digital camera.

http://maxmax.com/

They have some example before/after images to give you a feeling for
what it's like not to have an anti-moire filter. There are certainly
cases where the filter does more harm than good.

--
Aaron
http://www.fisheyegallery.com
http://www.singleservingphoto.com

"Aaron" wrote in message
...
And lo, Rich emerged from the ether
and spake thus:
Is it possible? It would allow for full resolution exploitation of a
sensor if this could be done in PS
or some other program. In some instances, moire never shows up, in
others it does. Why not leave the images where it doesn't show up
alone?

It's definitely possible. MaxMax, the somewhat venerable service
company known for IR conversions, offers what they call "HotRod"
service, which involves removing the anti-moire filter from your
digital camera.

http://maxmax.com/

They have some example before/after images to give you a feeling for
what it's like not to have an anti-moire filter. There are certainly
cases where the filter does more harm than good.

--
Aaron
http://www.fisheyegallery.com
http://www.singleservingphoto.com


But you had better like the look of moiré because without that filter or if
you camera has a weak one (the Pentax K10D) do that you have more sharpness
there is no way post process to get rid of it without major blurring.
Personally, I would rather have the "it shows only on certain patterns
otherwise isn't there with a balance of image detail and sharpness.) So far
I think most companies do a decent job of balancing the two.

=(8)

=(8) wrote on Wed, 13 Jun 2007 07:56:11 -0700:

"Aaron" wrote in message
...
?? And lo, Rich emerged from the ether
?? and spake thus:
?? Is it possible? It would allow for full resolution
?? exploitation of a sensor if this could be done in PS or
?? some other program. In some instances, moire never shows
?? up, in others it does. Why not leave the images where it
?? doesn't show up alone?
??
?? It's definitely possible. MaxMax, the somewhat venerable
?? service company known for IR conversions, offers what they
?? call "HotRod" service, which involves removing the
?? anti-moire filter from your digital camera.
??
?? http://maxmax.com/
??
?? They have some example before/after images to give you a
?? feeling for what it's like not to have an anti-moire
?? filter. There are certainly cases where the filter does
?? more harm than good.
??
But you had better like the look of moiré because without
that filter or if you camera has a weak one (the Pentax K10D)

I don't have any examples to try it on but relatively
inexpensive programs like PrintShop have Moire removal. My Canon
scanner can also be set in an anti-Moire mode.

James Silverton
Potomac, Maryland

E-mail, with obvious alterations:
not.jim.silverton.at.verizon.not

"James Silverton" wrote in message
news:q6Ubi.7151$pd5.667@trnddc02...
=(8) wrote on Wed, 13 Jun 2007 07:56:11 -0700:

"Aaron" wrote in message
...
?? And lo, Rich emerged from the ether
?? and spake thus:
?? Is it possible? It would allow for full resolution
?? exploitation of a sensor if this could be done in PS or
?? some other program. In some instances, moire never shows
?? up, in others it does. Why not leave the images where it
?? doesn't show up alone?
??
?? It's definitely possible. MaxMax, the somewhat venerable
?? service company known for IR conversions, offers what they
?? call "HotRod" service, which involves removing the
?? anti-moire filter from your digital camera.
??
?? http://maxmax.com/
??
?? They have some example before/after images to give you a
?? feeling for what it's like not to have an anti-moire
?? filter. There are certainly cases where the filter does
?? more harm than good.
??
But you had better like the look of moiré because without
that filter or if you camera has a weak one (the Pentax K10D)

I don't have any examples to try it on but relatively inexpensive programs
like PrintShop have Moire removal. My Canon scanner can also be set in an
anti-Moire mode.

James Silverton
Potomac, Maryland

E-mail, with obvious alterations: not.jim.silverton.at.verizon.not

Yes, and it is a simple blur, you loose image detail and you loose a lot.
Once the pixels are arranged in a pattern that is a moiré pattern the only
way to get rid of it is to either add enough noise to obliterate it or you
blur it out. There is no way to do anything other than that to it. You can't
add detail that isn't there and if there was detail there you wouldn't have
a moiré pattern because a moiré pattern isn't detail.

=(8)

"=(8)" wrote:

I don't have any examples to try it on but relatively inexpensive
programs like PrintShop have Moire removal. My Canon scanner can also be
set in an anti-Moire mode.

James Silverton
Potomac, Maryland

E-mail, with obvious alterations: not.jim.silverton.at.verizon.not

Yes, and it is a simple blur, you loose image detail and you loose a lot.
Once the pixels are arranged in a pattern that is a moiré pattern the only
way to get rid of it is to either add enough noise to obliterate it or you
blur it out. There is no way to do anything other than that to it. You
can't add detail that isn't there and if there was detail there you
wouldn't have a moiré pattern because a moiré pattern isn't detail.

Exactly. Note, by the way that digital images not only cannot resolve above
the Nyquist frequency, they can't resolve above the Nyquist frequency times
the Kell factor.

Here's a game to play. First of all accept the following definition: the
"reliable resolution" of a camera is the maximum resolution at which both
the relative intensities and relative widths of features in an image are
correctly rendered. If you don't care if your photographs bear no relation
to the subject, you can stop hereg.

First, download the resolution chart images for the Canon 10D and Sigma SD10
from this page.

http://www.dpreview.com/reviews/sigmasd10/page18.asp

Open both in your favorite editor, apply a bit of sharpening, and observe
both at 400%.

Now, keeping in mind that there are exactly nine lines in the test pattern,
start at the wide end of the horizontal pattern and find the first point
(highest resolution) where the where the camera fails to render the pattern
as nine lines of equal darkness. The point below that is the "reliable
resolution".

To my eye, the Canon 10D, the camera produces intensity variations at "15"
(1500 lph) and 9 even lines at "14" (1400 lph).

The Sigma is having nasty jaggy problems from the start, and is showing
different width lines at "9" (900 lph), and intensity variations at "11". So
it's "8" if you need correct feature widths, and "10" if you just require
correct feature intensities.

So I see the 10D has having a "reliable resolution" of around 1400 lph, and
the SD10 of having a "reliable" resolution of around 1000 lph (since I'm in
a generous mood today: in a more serious mood, since the SD10 messes up the
line widths at 900 lph, it's really an 800 lph camera). A 40% difference is
an enormous difference, but a lot of people don't care that their images are
correctly resolved, and think that the SD9/SD10 are roughly similar to the
6MP dSLRs.

So here's a question: how many pixels do these cameras require to reliably
resolve a line? The 10D requires 2000/1400 = 1.43 (to get feature width and
intensities OK), and the SD10 requires 1536/800 = 1.92 for correct feature
widths and 1536/1000 = 1.56 for correct feature intensities.

So my take is that the low-pass filter _improves_ resolution for people who
require that features that appear in their images actually correspond
correctly to features that exist in the subject.

David J. Littleboy
Tokyo, Japan