Avoiding Moire Patterns

[Chris Harding]

Hi All

After finding moire patterns in my bridal arrival footage whilst a brick wall got in the way when the limo pulled up (Luckily I didn't have to use that bit of footage as it was just the limo trying to park correctly!!!) it has made me generally more concious of the effect during filming!!!

I was watching a commercial program this afternoon and the camera was switching back and forth between talent all sitting having dinner and the chair backs (all matching) were upholstered and the camera picked up moire patterns on each and every chair back and they were extremely prominent!!!! The commercial producers obviously have the same problem too but don't seem to worry about it. I often seen it in episodes of MASH so even footage shot on film and run thru the telecine process is not immune either!!!

I'm reluctant to go back thru years of wedding footage but I was wondering if anyone else notices them when patterned surfaces are in the frame????

I wonder if there are any special rules for avoiding moire patterns whilst filming????

Any bright ideas from the experts how to avoid them?????

Chris

[Daniel Browning]

Originally Posted by Chris Harding

I was watching a commercial program this afternoon and the camera was switching back and forth between talent all sitting having dinner and the chair backs (all matching) were upholstered and the camera picked up moire patterns on each and every chair back and they were extremely prominent!!!!

Yep.

Originally Posted by Chris Harding

The commercial producers obviously have the same problem too but don't seem to worry about it. I often seen it in episodes of MASH so even footage shot on film and run thru the telecine process is not immune either!!!

That's correct.

Originally Posted by Chris Harding

I'm reluctant to go back thru years of wedding footage but I was wondering if anyone else notices them when patterned surfaces are in the frame????

It drives me crazy. Makes me want to claw my eyes out. But brides don't seem to notice. At all.

Originally Posted by Chris Harding

I wonder if there are any special rules for avoiding moire patterns whilst filming????

One is to not add moire in post. One common way is in how you downsample (e.g. from HD to SD). Most downsample algorithms do a very bad job and add moire.

Another is to use a good camera. See this page for a report on many cameras and how bad their aliasing (moire is one type of aliasing artifacts) is:

BBC R&D White Paper WHP034 - Alan Roberts

Originally Posted by Chris Harding

Any bright ideas from the experts how to avoid them?????

If you can't switch cameras, the only other option is to blur detail optically, such as with diffraction or a softening filter.

[Dave Blackhurst]

I never noticed all the artifacts, moire patterns, and goof ups until I started shooting/editing... now I see all that stuff on practically everything broadcast.

I doubt ANYONE other than someone with experience will ever notice, and as you've already figured out, there's not much you can do about it... some things you just live with.

[Chris Harding]

Hi Dave

You are 100% correct..I now see them on tons of broadcast programs too!! Funny thing is that normally I would not have shot the sequence if I was using tape and I just shoot what I need and pause!! With AVCHD cameras everytime you pause, it creates a new clip and each card can only handle 99 clips so to "conserve" clips I tend to let the camera run and film more than I need and that bit was, in fact cut out in post as the bride doesn't really want to see her limo struggling to get into position!!

Does anyone know if a moire pattern is visible in your EVF??? To be honest I have never seen one! I went to the trouble of playing the segment back in the camera just to satisfy myself and it shows on the LCD clearly!! I can actually remember having these as coloured patterns on house roofs in the good ole VHS days..both with CCD and even Saticon tube cameras!!!

Chris

[Daniel Browning]

Originally Posted by Chris Harding

Does anyone know if a moire pattern is visible in your EVF?

Yes. (In fact, many times there are patterns visible in the EVF that do not exist in the recorded image, which is because the method used to create the EVF image can cause moire itself.)