Moire shooting LED signs

Started Mar 3, 2010 | Discussions
StrangerTF
Junior MemberPosts: 36
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Moire shooting LED signs
Mar 3, 2010

Although not a photographer by trade I frequently need to photograph a large electronic sign as part of my job. Mainly this is for proof of performance for clients who buy time on the sign, but it is also important for the photos to show their creative efforts at the best. Problem is, that pointing a tiny, dense matrix of red green and blue sensors at a matrix of red green and blue LEDs seems to be a recipe for some especially hideous moire effects. For example, this is a detail from a photo taken with a Lumix LX3, and shows an area of the sign that a human eye would read as white.

I have also used an old Canon 300D which produces ugly, although less intense moire than the LX3, which I attribute to its much larger sensor area and also lower pixel density, although perhaps other factors may be involved as well.

The magnitude of the problem varies depending on the colors, patterns and distances involved, but rarely goes away entirely.

I know moire is a fact of life in photography, especially digital, but I would appreciate input on how I could at least reduce it. I can disguise it somewhat in Photoshop, but I would prefer to have things looking better out of the camera, to the extent that it is possible to do so.

I am sort of an 'advanced novice' meaning that I have been taking photographs for a long time and understand, at least superficially, most of the basics, but in actual practice I go about it rather simply. Perhaps I am just not doing it well? I do not have a heavy investment in EF-S lenses for the Canon, just the kit lens it came with and a relatively inexpensive long zoom, so switching systems is not a big deal to me.

Here is what I have thought of so far that might lessen moire, although I hope their may be other alternatives as well:

  1. use a camera with a larger sensor (like the Canon EOS 5D).

  2. use a camera with a Foveon sensor (like the Sigma SD14)

  3. Use film

1. Larger Sensor

This seems theoretically OK but I wonder in practice. Newer cameras with extra big sensors tend to also pack in higher resolution, and I have read some complaints (about the EOS 5D in particular) about significant Moire. Also, Full Frame sensors are expensive and I doubt my employers will foot the bill for $3K or so of gear.

2. Foveon Sensors

This seems like it may hold some potential. My understanding is that these cameras are virtually free of color moire by their very nature, although I have not had the chance to handle one yet. I would still have to deal with dark/light moire, I guess, but that would be one less issue to have. Unfortunately, I don't know anyone that has one (or a full frame sensor camera) so I am not able to try it on the sign. Sigma SD14 bodies are not too costly, especially second hand, lenses I am less sure of. I am aware that the SD14 has many critics, and is considered by some to be a niche camera, but perhaps this is one of its niches?

3 Film

I plan to try this, just to see, but it is not really a solution. I need much faster turnaround than film allows, and lack the facilities at work for heavy scanning.

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Any suggestions or comments? Thanks in advance for any input.

Joves
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Re: Moire shooting LED signs
In reply to StrangerTF, Mar 3, 2010

Well it is more the case of the AA filter over the sensor that affect the moire over sensor size from my understanding. Most of the filters are in the 30% range to lessen the effect. I shoot nature and wildlife myself and, am think of having my filter changed out to no AA which will increase the moire but, will give me more detail. You might try and see which manufacturer has the strongest with the best results for IQ. That is really all I can think of.
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FrankieJ
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Re: Moire shooting LED signs
In reply to Joves, Mar 3, 2010

Not sure if this may help or not, I shoot a lot of architecture and I get a lot of moire' off of horizontals, brick facades, rows of window frames, etc.
I began turning my camera diagonal then correcting in post.
It helps with straight lines, not sure if it will help with the little LED dots.
Worth a try...
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dave_lamb
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Rotation or slight de-focus
In reply to StrangerTF, Mar 3, 2010

Greetings,

I do a bit of LCD metrology using a digital camera which can result in horrendous moire (as in your examples). As someone else mentioned, slight rotation of the camera can help reduce the visibility of moire. I have also found that de-focusing slightly from the exact plane of the display is very effective (especially when shooting at large apertures). This may or may not be suitable for your application, but it might be worth a try.

Good luck!

Dave.

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StrangerTF
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Re: Rotation or slight de-focus
In reply to dave_lamb, Mar 4, 2010

Thanks to all who have replied. I will try out using slightly off focus and angles in the morning and see if I get improvement.

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Danack
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Re: Moire shooting LED signs
In reply to StrangerTF, Mar 4, 2010

Any chance of uploading a raw file so that we can have a play with processing it?

The only thing I can suggest are make sure you use a slow exposure - most LED display don't drive the constantly but flash them on/off very fast. You should try taking an picture with an exposure of say a half of a second so see if that is happening.

"I know moire is a fact of life in photography,"

I don't believe that what you are seeing is moire. Moire effect happen at the pixel level. Unless your camera is producing more pixels in the output picture than are on it's sensor (i.e. there's some kind of upscaling going on) the effect you're seeing here is across too many pixels to be moire.

It's more likely either to be due to flourescence across the pixels in the LED display which you're eye can't see but the camera can (due to your eye having a lower resolution than your camera) or some kind of temporal effect, where, again your eye can't see the pattern, but your camear can.

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StrangerTF
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Re: Any chance of uploading a raw file..
In reply to Danack, Mar 5, 2010

I am chagrined to confess I didn't start shooting in raw format until recently--I did not understand the benefits, or even how to open raw files, at first. I only have these bad shots in jpeg (maybe that's part of the problem?), but haven't shot the sign in raw more than a few times. Next time I get a really bad moire, or whatever it is, in raw I will see if I can make it available.

The only thing I can suggest are make sure you use a slow exposure -

I will try that.

most LED display don't drive the constantly but flash them on/off very fast. You should try taking an picture with an exposure of say a half of a second so see if that is happening.'

I don't believe that what you are seeing is moire. Moire effect happen at the pixel level. Unless your camera is producing more pixels in the output picture than are on it's sensor (i.e. there's some kind of upscaling going on) the effect you're seeing here is across too many pixels to be moire.

Not sure. It certainly looks like moire to me, but I am no expert.

It's more likely either to be due to flourescence across the pixels in the LED display which you're eye can't see but the camera can (due to your eye having a lower resolution than your camera) or some kind of temporal effect, where, again your eye can't see the pattern, but your camera can.

The part of the sign that gives me these problem runs at 30 fps, non-interlaced. The change from one frame to the next is pretty consistent across all the LEDs--I have looked at many videos frame by frame and there is never any discernible blanking between frames(also much less severe moire-ish patterning than in a much higher res still image). Also, colors that are close to pure red, green or blue show up clean as a smooth, freshly painted wall. White is the worst.

I don't know what that says, pro or con about the possibility of it being a temporal effect.

Anyway, thanks for the suggestions.

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joseph costa
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Re: Moire shooting LED signs
In reply to StrangerTF, Mar 6, 2010

try increasing your physical distance from the lights and use an open aperture if you have the ability. that should help with that. you get really close and the light coming off the signs are pretty bright..this could contribute to the moire effect if the sensor cannot handle it.

StrangerTF wrote:

Although not a photographer by trade I frequently need to photograph a large electronic sign as part of my job. Mainly this is for proof of performance for clients who buy time on the sign, but it is also important for the photos to show their creative efforts at the best. Problem is, that pointing a tiny, dense matrix of red green and blue sensors at a matrix of red green and blue LEDs seems to be a recipe for some especially hideous moire effects. For example, this is a detail from a photo taken with a Lumix LX3, and shows an area of the sign that a human eye would read as white.

I have also used an old Canon 300D which produces ugly, although less intense moire than the LX3, which I attribute to its much larger sensor area and also lower pixel density, although perhaps other factors may be involved as well.

The magnitude of the problem varies depending on the colors, patterns and distances involved, but rarely goes away entirely.

I know moire is a fact of life in photography, especially digital, but I would appreciate input on how I could at least reduce it. I can disguise it somewhat in Photoshop, but I would prefer to have things looking better out of the camera, to the extent that it is possible to do so.

I am sort of an 'advanced novice' meaning that I have been taking photographs for a long time and understand, at least superficially, most of the basics, but in actual practice I go about it rather simply. Perhaps I am just not doing it well? I do not have a heavy investment in EF-S lenses for the Canon, just the kit lens it came with and a relatively inexpensive long zoom, so switching systems is not a big deal to me.

Here is what I have thought of so far that might lessen moire, although I hope their may be other alternatives as well:

  1. use a camera with a larger sensor (like the Canon EOS 5D).

  2. use a camera with a Foveon sensor (like the Sigma SD14)

  3. Use film

1. Larger Sensor

This seems theoretically OK but I wonder in practice. Newer cameras with extra big sensors tend to also pack in higher resolution, and I have read some complaints (about the EOS 5D in particular) about significant Moire. Also, Full Frame sensors are expensive and I doubt my employers will foot the bill for $3K or so of gear.

2. Foveon Sensors

This seems like it may hold some potential. My understanding is that these cameras are virtually free of color moire by their very nature, although I have not had the chance to handle one yet. I would still have to deal with dark/light moire, I guess, but that would be one less issue to have. Unfortunately, I don't know anyone that has one (or a full frame sensor camera) so I am not able to try it on the sign. Sigma SD14 bodies are not too costly, especially second hand, lenses I am less sure of. I am aware that the SD14 has many critics, and is considered by some to be a niche camera, but perhaps this is one of its niches?

3 Film

I plan to try this, just to see, but it is not really a solution. I need much faster turnaround than film allows, and lack the facilities at work for heavy scanning.

-- hide signature --

Any suggestions or comments? Thanks in advance for any input.

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comeon
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proof of performance ..
In reply to joseph costa, Mar 6, 2010

i dont know how small a crop you have posted of the actual sign .

However if it just for proof of performance i doubt the client is pixel peeping so why would it matter so much ??

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StrangerTF
Junior MemberPosts: 36
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Re: if it just for proof of performance...
In reply to comeon, Mar 6, 2010

comeon wrote:

i dont know how small a crop you have posted of the actual sign .

A fair question. Each of those stripes is one meter high (or just over 3 ft, if you prefer). So the samples are both about 3 meters (or 10 feet square) The actual sign is 38 meters long by just under 8 meters high (124x26 feet) So this is a small but not completely insignificant chunk of the final image.

However if it just for proof of performance i doubt the client is pixel peeping so why

Down-sampled to a convenient size for email, it is true the moire is no longer obvious-- as moire . Unfortunately, it is still very visible as blotchy areas of discoloration and uneven brightness. I could preface every email with the caveat 'Your ad looks beautiful, I am just a lousy photographer" and I would still get replies asking if their ad really had random-looking color splotches.

By taking a lot of shots I can always eventually get one that is passable with a some Photoshop work, but I would prefer to get better than passable with less time spent post-processing. I have gotten many suggestions I haven't had the chance to try out yet, though so I have some hope.

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Svein Eriksen
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Re: if it just for proof of performance...
In reply to StrangerTF, Mar 6, 2010

I think it's interference patterns beteween the pixels on the LCD and the sensor like you said in the original post. I'm not sure if it's moire or not, but that's not really that important either.

I've seen similar effects taking pictures of small LCD-screens, and sometimes it's worse than other without an obvious reason. Taking the shots on angle and correcting in postprocessing like someone suggested might help, and varying the distance (or zoom) might also help.

I'm usually able to get a pretty good result by using a gaussian blur in photohsop though. It will make your image less sharp, but you can improve sharpness again by downsizeing afterwards (and sharpen if needed). Of course provided that you don't need the full resolution of your camera.

The problem is similar to scanning printed material. Many scanners have a descreen function which will do this automatically, but you can also find descriptiosn of a "manual descreen" on the net.

http://www.scantips.com/basics6b.html
http://www.descreen.net/eng/help/descreen/home/descreen_manual.htm

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