"Moire Effect" - Camera to Offset Lithography - Important Defect?

In article . com,
tomm42 wrote:

Don't know if you are over analizing a digital image, are you
photographing images that are made with offset lithography or using
digital images in offset lithography.

I will be using digital images in offset lithography, not photographing
images that are made with offset lithography.


...I work for a hospital magazine that requires digital to avoid
scanning costs. Is offset lithography significantly different
from these applications? I really would like to know

Offset litho' is different in the sense that very large high res'
images of blank areas like flesh tones are liable to be in the final
litho' image, whereas newspaper photo's are less liable to be "fashion
shots" with large areas of skin tones.

Also, the newspaper editor can change the size of the image in his
paper, to minimize any Moire pattern by making his final image an exact
multiple of the CCD image size.

Clients for extremely high cost fashion images are less inclined to
approve any change in final image size.



My Google sources explaining the Moire effect, claim it creates banding
even in areas that have no patterns, like plain walls, sky, skin tones,
etc.

Has something to do with the dot pattern in the camera CCD being
"out-of-sync" with the dot pattern of the displayed image in the
newspaper or slick magazine.

According to the Google source, the Moire effect only occurs when the
final image is created with a regular dot pattern, as in a newspaper
photograph, or a magazine offset litho' rendition.

Print to regular photographic paper that has no dot pattern, and the
Moire effect should never occur.

In my mind, this means the Moire effect is different than the colored
fringes on fine lines, commonly observed when photographing plaid
shirts etc.

Mark Conrad wrote:

Great suggestion. I can then run some tests by submitting my photo's
of blank areas to an offset lithography shop, being careful to ensure
that the litho' image size is _not_ exact multiples of the CCD image
size, and put this entire "Moire effect" issue to rest.

'Course, the litho' guys will call the guys in the white coats to haul
me away, when I ask them to process images of blank walls.g

Test for two cases that give digital camera the most problems, fine
patterns, like you might find in some fabrics, and detail that is in
color, such as red lines on a blue background, or the other way around.

You should not have a problem with moire pattens between the cameras
pixels and the screening, at least if some care is done in the
screening. The screening is just a resampling of the digital image and
this normally does not cause a problem, at least if the person doing
the screening knows even a little about what they are doing (which they
might not).

A moire pattern is one form of aliasing, lines that are jegged is
another. I can make it show up at will, shoting through a screen at an
angle usning a larger f number will do it. but it is pretty rare in the
kind of photos I take. But be aware that you subject matter can have a
large impact on how often you see it.

Scott

"Colin D" wrote in message
...


Mark Conrad wrote:

I am seriousely contemplating buying a new 12.8 MP Canon.

Would appreciate advice from actual owners of that camera.

Contemplated usage will be mainly for producing offset lithography
phamplets and possibly larger 8 x 11 inch "slick" brochers.

My setup will be an Intel-based Mac using Photoshop (or other raw
editor) for editing the raw digital image from the Canon.

I have heard that the Canon has a fairly bad Moire effect, but I guess
all digital cameras in that price range are afflicted with the
Moire-effect problem, when offset lithography is used.
(colored bands in areas that should be plain, like flesh tones)

According to Hassleblad press releases, their newest 39 MP camera will
incorporate Moire-effect reduction techniques, however that camera will
be too costly for most users. I heard $43,000 (US).

I am essentially new to digital photography. The Canon 12.8-MP might
be my first digital camera of any kind.

Mark-

Moire is not a problem with Canon cameras, thanks to a fairly aggressive
Anti-aliasing filter, but the camera with the reputation for moire is
the Nikon D70, which has a less aggressive filter to try to maintain
sharpness. While the ex-camera image from a Canon appears less sharp
than from a D70, unsharp masking in Photoshop will restore all the
sharpness you want, and you don't have the disadvantage of risking
moire.

Of course, if you will be shooting half-tone printed images, then moire
is almost certain to show up with any digital camera - except perhaps
the Sigma with its Foveon chip, but the color results from Foveons
leaves a lot to be desired. If you want accurate color, specially skin
tones, a Foveon won't do it.

Colin D.

I find the colors from my Sigma to be just fine - with the exception of
skintones as you noted but those are easily corrected. It's also an
intermittent problem, not a constant one. FWIW, did you view the site I
linked to? The fabric example used to show the moire artifacts on Foveon's
site is almost identical to a shirt I have - even the color. I could not
reproduce much of any moire artifacts using my shirt and a Nikon D50. How
much of a real probelm is this for most DSLRs anyway?

In message . com,
wrote:

I primarily shoot motion picture stuff, and I'm known in my circles as
a rather moire-conscious cinematographer anytime I shoot on a video
format (most of the past year and a half). I'm confident that my 20d
didn't produce any moire... it isn't something that I simply "didn't
notice".

http://www.pbase.com/image/37173876
--


John P Sheehy

I primarily shoot motion picture stuff, and I'm known in my circles as
a rather moire-conscious cinematographer anytime I shoot on a video
format (most of the past year and a half). I'm confident that my 20d
didn't produce any moire... it isn't something that I simply "didn't
notice".

http://www.pbase.com/image/37173876


I didn't say it was impossible, I said I hadn't seen it in my
photographs even when shooting various "real-world" subjects noted for
producing moire.

I didn't shoot any monitors though, and I don't think I've ever had
need to do so in photography. I suppose if the original poster is
shooting alot of monitors he should avoid the 20d and likely every
other prosumer digital camera on the market.

Will

In message .com,
wrote:

I didn't say it was impossible, I said I hadn't seen it

.... and I didn't say anything. I just linked a photo.

in my
photographs even when shooting various "real-world" subjects noted for
producing moire.

I didn't shoot any monitors though, and I don't think I've ever had
need to do so in photography. I suppose if the original poster is
shooting alot of monitors he should avoid the 20d and likely every
other prosumer digital camera on the market.

If it can happen on a monitor, it can happen on any pattern of colored
dots with the same angular resolution, reflective or source. A sharp
lens "helps" (I was using the Tamron 90mm Di Macro lens, an extremely
sharp lens).
--


John P Sheehy

In article , Mark Conrad
wrote:

Wonder where I went wrong in my long winded "analysis".

Think I will go back to my Google sources, and read them again.


Well guys, I went back and checked my Google sources.

I was wrong in my posts - - - I hate when that happens.

The "Moire Effect" is totally different than I thought it was.

Apparently, like everyone was trying to tell me, patterns in the
original object-being-photographed are necessary to trigger the Moire
effect.

I was dead wrong when I posted that there can be Moire defects when
photographing a plain sky, or a wall without any texture, or broad
areas of evenly colored skin tones.


Also, I read a very large number of posts from poor devils who had
Moire defects in their final images. Those guys often tried
everything suggested to them by pros, and _still_ could not get rid
of the Moire defects.

It seems to be something of a black art, as to what works and what
doesn't work.

Even ordinary film cameras are sometimes affected by Moire defects.

It was pretty well agreed that some models of Nikon are afflicted with
more than their share of Moire problems.

Come to think of it, I sometimes see Moire defects on my television,
when the weatherman wears some types of patterned ties.g

Hope the Canon 12.8 MP camera I am considering buying only has its
"ordinary" share of Moire problems.

Apparently this is something we all have to live with, trying this and
that to minimize Moire defects.



Sorry everyone, for wasting all your time because of my own inept
reading of stuff about Moire.

Mark-

Mark Conrad wrote:
In article , Mark Conrad
wrote:


Wonder where I went wrong in my long winded "analysis".

Think I will go back to my Google sources, and read them again.



Well guys, I went back and checked my Google sources.

I was wrong in my posts - - - I hate when that happens.

Surprise, surprise.

Yet another newsgroup polluted by "Mark Conrad". "All Things Mopar",
meet your doppelganger "Mark Conrad".

The "Mark Conrad" FAQ:

http://www.codecomments.com/archive2...-4-182180.html

I'm sure Jim Hill can update it to include a 7(c):

b) People competent in digital imaging risk high blood pressure by
reading his explanations of how things work. Among the
risks associated with high blood pressure are stroke, heart
attack, acid reflux disease, and shortened life span.

Greg


--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

In message ,
Gisle Hannemyr wrote:

Actually, the Canon EOS 5D, along with the Nikon D70, has a
fairly weak antialias-filter and is therefore more subject
to moire than, say, the EOS 20D or 30D.

I don't know about the 20D; with a very sharp lens the RAW data will go
through almost 100% contrast in the space of 2 pixels (3 inclusive).
That's the same bayer color, so there isn't a possibility that it a
color sensitivity issue. I don't think the 20D's AA filter is all that
strong. It took almost a pixel more to do the same with the 10D, and
that is less taxing on the lens, with its coarser pixel pitch.
--


John P Sheehy

Mark Conrad wrote:
...
I am sorely tempted to consider buying a Nikon instead, then forget
about using high priced offset lithography output for my short runs of
phamphets, brochures - - - then print the final _sharp_ Nikon images
to regular photographic paper, where the Moire effect does not exist.
...

It the Moire effect is visible in the picture talken by the camera, it will be
visible in the printed photograph regardless of how you print it.