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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Moire Issues

David Fairbanks

David Fairbanks

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Has anyone heard if Red has mentioned moire. It's been a issue on electronic cameras since day one as far as I know. I'm sure they will have the absolute best processing to eliminate it.

Having shot with digital stills for years, I know that the higher the resolution of the sensor, the more susceptible you are to moire in fabrics like suit jackets and the like. Smaller images from large sensors can give you moire when the actual full size image doesn't have a problem. It's even worse when the small image doesn't show anything and the full size image is covered in it.

In stills the best way to elevate it is to change focal length slightly and reshoot the shot. This wont be practical in most situations with Red.
 
Low pass... I don't see that would do anything. But I also haven't messed with low pass filters (or high pass for that matter).
 
I don't understand moire. Is that a different word for alising?
 
Moire is interference patterns.
The texture in cloth for instance will render in odd patterns when it is captured by a patterened sensor.
004WFK-11367184.jpg
 
If it's over the sensor, we wouldn't have the option of removing it. But if it's not a noticable amount of softening, it probably wouldn't matter.

Surely my D2X doesn't have it, it loves to moire.
 
Every Bayer based sensor should have a OLPF that matches the sensors resolution.
Current pro DSLR's seem to have a filter that is tuned for a sharper image and will still show a little moiré in worst case situations.
The RED camera will have one as well. I believe some of the first shots previewed was without any filter, but the recent ones were with it fitted.
 
There is some issues with the hair in the Bubblegirl clip. But it's also mentioned that it's shot without a low pass filter.
 
Hi,

If you can turn off any sharpening (Red does not have any) you should not have big issues.

Remember the project is 'work in progress', I have not seen any problems with images so far.

Stephen
 
My experience is that it has nothing to do with sharpening. It's just the interference of the two patterns.

The images they have produced have been amazing, and it is a work in progress, so time will tell.
 
Moire is visible aliassing. Being a sampled system, the sensor will exhibit aliassing on images if it is asked to record detail smaller than 1 pixel in dimension.

The above, is applicable to all sensors, including 3 chip systems, RGB silicon filter sensors etc. That's why all sampled systems need an anti-alias filter, which in a camera is called an OLPF or optical low-pass filter. The name tells you what it does. It passes though, or leave un-effected low frequencies, and attenuates high frequencies. We want to make sure than the sensor isn't asked to sample any frequencies or details so high that they would introduce aliassing.

With a bayer pattern CFA, this is even more important because moire on a bayer pattern sensor shows up as colour moire as well as luma moire. Colour moire, as shown above is quite nasty.

Now when we did our first mysterium shots, our OLPF had not arrived, so we just shot things as it, and I used a demosaic that was designed to be gentle on the eyes and remove some of the moire that could occur. It can't get everything, but was a good solution.

Now we have an OLPF in place, and we can be more free with our choice of demosaic. We don't get nasty colour moire on edges, and the slight softening makes for a very smooth, continous image, with no visible pixels or aliassing.

Aliassing makes it harder to suspend disbelief as we don't see aliassing in the real world. (we do see moire when two fine patterns are overlayed though). We don't see fine detail having steppy edges or being made of discrete pixels.

Excessive edge sharpness is know to cause judder in slow fps recording - think 24p.

Because in motion, aliassing changes on each frame, it's more noticible than on a still as it's almost as if the pixels are waving at you saying "look at me". On a still image, if there's a bit of moire, you can paint it out. On a movie, that would be terrible!

Graeme
 
Aliassing makes it harder to suspend disbelief as we don't see aliassing in the real world.
We do see aliasing on stuff that moves (although motion blur tends to act as a low pass filter). But other than that, for stationary stuff, we see incredibly low/no aliasing.

We also seem to get less aliasing in dim conditions. You can test this out by printing out a zone plate test pattern and holding it in your hands and moving it around. You can get one off here: (scroll down)
http://www.ecinemasys.com/products/edp100/edp100_lcd_vs_crt.htm

Or
http://www.worldserver.com/turk/opensource/#ZonePlate
 
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