7D Moire/aliasing !
 

I shot some footage today with my 7D of some brick walls at a distance, and lo and behold...that nasty moire/aliasing pattern! It really is awfully obvious. I researched the heck out of this camera before I bought it a few days ago and this didn't come up as a paralyzing problem, but it really is a sore thumb in such an otherwise great piece of hardware.

So my questions are thus:
Why did I buy this camera?

Also,
Is it fixable? In other words, can I expect a firmware update to set things right, or is this wishful thinking? I understand the concept of how the sensor "downscales" from the sensor to 1920x1080 in the most lazy way possible--skipping lines, boo!--so can a rewrite of the firmware fix this, or is reasonably clean footage of horizontal patterns simply outside the capabilities of the camera?

You need better skill in the search, the moire and aliasing was well known and all over the net, the best solution is don't use it as wide infinite dof camera, but if you have to, what I do is I have the Zacuto so I can see aliasing crop up on buildings like that and I slightly out of focus it until the moire goes away and then add a little sharpening in post.

The best way to fix it is:
1) Put an actor a number of steps in front of the brick wall.
2) Set the lens to f/4 or wider.
3) Focus on the actor. (just make sure they're not wearing a finely patterned shirt.)

You can also take the edge off of aliasing with a diffusion filter, like a Soft/fx, pro-mist, or glimmerglass. There's no magic formula. It varies by lens and the look that you want. If you go too soft, you get the boudoir look. If you don't go soft enough, you won't see a difference.

These filters also reduce contrast. That makes it really hard to give a cookbook answer. If the contrast of your scene is already too low (say, on an overcast day), a diffusion filter can look terrible. On a sunny day, it might look great.

Just go shoot some thin DOF in low light and you'll remember. ;)

Jon and Khoi Pham gave you good suggestions already. I can't think of anything else to add.

I don't know for certain, but I strongly suspect it's a hardware limitation.

I didn't say I didn't know about it, It was simply not emphasized to me as major nail in the coffin.

Canon 7d Tips Blog Archive Canon 7D Moire pattern test

The focus fix came to me as I was playing around with it--it's still unfortunate, how can you not use a camera at full wide? I can deal with limitations, just frustrating to encounter one that could have been avoided (Canon I'm looking at you).

Don't look at me. I emphasized the problem so much that people around here started giving me the stink eye. :)

That's what my XH-A1 is for. ;)

Actually, I don't think it could have been avoided. I think their only choice was to give us flawed video or no video at all. I'm sure that eventually the hardware will catch up to the level we'd like, but for now we have to grin and bear it.

Because it only cost $1600. It's solid for the price. For the price.

I don't think it would make sense to say that it could have been avoided. There is some pretty complex number crunching involved in downscaling an image of 21,100,000 pixels to one of 2,073,600. On top of everything else that's going on in creating the 264 stream.

I'd rather say, Canon has revolutionized what many of us can do, and the inevitable improvements in tech over the next 2-3 years will knock our socks off.

From your site Bill it seems you make indie features. So you're up against Z1U's, XH's, HVX's and just maybe a few EX1's. I think you look pretty good shooting 7D.

Unless you're screening it on a giant screen with a super-critical and technical audience, I think you're good to go even with a bit of aliasing in certain shots. But it would make sense to follow the advice above to reduce it as much as you can.

Or, return the 7D, gather up about $10,000 on top of that, and get a Scarlet in ... months.

Ben,
Not to be a jerk but when you say you researched the heck out of this camera and didn't realize the extent of the issue, I have to wonder where you researched. The ailasing issue has been discussed ad infinum in many forums until it seems that is all that is talked about. This forum may be an exception, I don't know. Personally it hasn't been that big of an issue for me, I just try to avoid situations where it will pop up.

Clearly, issues are downplayed by a lot of people who are antagonistic towards second-guessing their $2k purchase. Perfection of an image is a priority to some, not to others. My mistake was not taking this into account.

The problem is incredibly disappointing to me. I may be an exception, I don't know.

I'm in my last year of electrical engineering at UMD. They teach us that our major provides us the ability to take the complexity of real life and engineer solutions. I'm not going to pretend I'm familiar with the DSLR systems, but I am familiar with VLSI circuit design and DSP. This is a DSP problem: it is possible to engineer a solution. This was not an impasse, this was a decision to ignore the problem. As has been discussed on this forum and others, this is primarily a photographic camera. If the engineering emphasis had been on video the issue would have certainly been addressed. I have no illusions about the reasons behind the problem, I just feel a bit let down.

Avoiding Aliasing
 

I'm strongly considering buying a 7D. The only thing holding me back is the aliasing/moire issue. Whenever I see a horrible still-grab posted, I think about playing it safe with a more 'traditional' model, but then I remember all the amazing videos I've seen posted and wonder why it never affected any them. Can't take the back and forth much longer!

Is this a safe choice for someone whose only HD camera will be the 7D? What do I need to stay away from aliasing when using the 7D? What triggers it? Just a bunch of straight, parallel lines? I'd rather exclude all problematic objects/shots from the storyboards than have to correct for aliasing during shooting or in post.

Also, if I export to a lower res for displaying the video on the web (say 720 or 480) will this hide the aliasing or make it worse?

You make it sound like a lot of money. Not in this biz ;) Believe me, the 7D is a phenomenal steal. Unheard of bargain.

Name me a camera (any price) that produces a "perfect" image. Every camera has severe drawbacks, even the much-worshipped Red One.

Let me put it this way, I'd rather be a musician than an audiophile. Embrace the flaws and make art.

The 7D isn't an every down back. It's kind of like Reggie Bush. Used in the right situations, it's golden. If you want a one size fits all video camera, you need to spend over 15 grand. A cam with a seamless image, shallow DOF, low light ability, multiple frame rates doesn't exist below that mark.

And seriously, I can't imagine how anyone, at this point, could complain about being surprised that the 7d has moire issues. It's almost cliche to even talk about it.

Justin,
For 2K, nothing comes close. Not having to mess with DOF adapters, great low light, stealth design (video cam posing as a still cam) and interchangable lenses make this an absolute steal. The bad issues of moire, jello and crappy audio are disadvantages you need to consider before purchase, but remember ALL cameras have achilles heels and you need to weigh those cons against what you are planning to use it for. Ben apherantly didn't and is upset about his purchase, so think it out carefully and if your doing alot of run-n-gun shooting (jello) or shots of buildings, fences, tiled roofs, striped shirts, verticle blinds etc (ailasing) you will have issues :)

Here's a "real world" use of the 7D on a car lot with buildings, cars, trees, etc. - lines everywhere - and it held up real nice like me thinks. Client liked it for sure. :) Footage is shown here raw and then graded. Used "flat" setting shot at 1080p24...

I agree. The 720p render doesn't have nearly as much aliasing as normal 7D footage. Did you use a slow f-number by any chance (e.g. f/16)?

That's a new. Didn't know 720 renders were cleaner. Supposedly native 720 (originating) is worse though.

Generally, they are. A quality downsampling algorithm will throw away both high frequency detail (resolution) as well as high frequency artifacts (e.g. aliasing). The low frequency detail and aliasing (e.g. moire) are left in place.

That said, what I actually meant by "the 720p render" was "Blake's 720p render of this specific video", to differentiate it from the lower-resolutions that Vimeo also provides. Sorry for the confusion.

Yes I did. I had no ND so I actually shot at f/22!

And I did upload a 720p H.264 Quicktime to Vimeo, downconverted from the original 1080p file.

Thanks. That explains why you didn't get any aliasing: diffraction took care of it. It was still sharp enough for 720p, though. Good work.

i think this video looks really good too but i think it was quite an easy one for the 7d to do well.. lots of matte colours, the sky, the buildings, the cars..

the shots i've had difficulty with have been much more textured - old brick buildings, trees, landscapes, clothes textures etc

i dont think vertical lines are necessarily some awful thing to avoid but more if the frame is full of extremely detailed stuff and the camera doesnt have any chance to say 'ok over here weve just got some blue so we can use our available resolution to take care of whats in the rest of the frame'..

i guess.. or else just the colours look very matte because of the diffraction!

Just to summarize, a way to minimize aliasing is:

-originate in 1080
-shoot with high F stops (F16,22)
-render footage to 720p in timeline
-cross fingers

or alternately, if filming a person (as opposed to landscape/cityscape)
- originate 1080
- shoot low F stops (2.8 and below)
- render 720p

No truth to this.

I usually render to 720 my 1080 material. The aliasing found in 1080 stays in the 720.

I agree with Ted. From my experience, unless you minimise the aliasing on the original footage (either by diffraction softening with a F stop of say F11, 16, 22 etc. or - most often a much better approach - going the other way and having a very shallow depth of field) then expect to see those horrible artifacts when problematic things are in the shot. I'd love to be proved wrong though!

Because of this I tend to use my EX3 for any overcranking work and leave the 7D in 1080p25 where it's aliasing is least problematic.

I agree that for perfections sake traditional cameras should be considered for certain scenes.

But let me share this;

In a very recent project, delivered Feb 5th, the scenario for having aliasing in scenes was very high. It was an urban real estate project.

I was aware moire and aliasing would show up in my shots due to thin lines in buildings.

I have done intensive chart tests to tell me the threshold for thin line sizes to trigger moire.

Having said that I decided to push it when I decided to shoot the wide facades of buildings with the 7D knowing it produces moire and artifacting.

I had our HD100 and HD200 with 35 adapter on standby but decided to "prove a point" that viewers don't care about us techies pixel peeping the image.

The gambit paid off cuz even though this was shown on a couple of huge screens (10.5 x 14 FEET) during the launch nobody noticed the limitations of the camera's binning method of CMOS reading.

The moire is there, so is aliasing. BUT -the viewers focused on the message, and the client(s) were very happy.

Heres the material I'm talking about.

Simply Life's Essentials http://exposureroom.com/getassetthum...4d28ba&size=sm

I've been realizing more and more what you're talking about Ted. I've done 3 paid projects with my D90 in the last several months. Even though I see all kinds of technical problems with the image, the clients were thrilled with the footage. I've been going back and forth about getting a 7D, but I think if the D90 can make the clients happy, then the 7D will do just fine.

What it comes down to is whether the amount of aliasing is noticeable and objectionable to the client, not to us. A little glimmer here and there is not terrible--the main subject's shirt, hair or eyebrows crawling is obviously a problem. Rainbows all over a brick wall may not be noticed under certain circumstances.

The key to all this is having external monitoring of the camera. That little LCD doesn't tell enough of the story a lot of time.

Unfortunately, sometimes whether or not the client will accept/notice is up to client...after i spent their money:) Being up front with the client before you are hired, telling them that at certain times a different camera angle/distance/background might be needed, helps. We did a television commercial where the client/creatives were on location, and told them the moire was a problem on a certain shot and we needed to block it a little differently. They were fine with new blocking...but they didn't notice the moire in their monitor either!

If you can make beautiful images, most people won't notice at all...like me watching Ted's video...


...Ted, you always make beautiful, creative films that i forgot i was watching for aliasing/moire examples... i watched a second time...and still forgot about aliasing/moire.
i didn't watch it a third time:)

Can anyone tell me if shutter speed effects Aliasing?

surely a higher shutter speed would exaggerate the effect, yes/no?

@Mike, Thanks! Its important to be aware how to provoke this defect so it can be addressed ideally at shooting stage. Addressing it in post is difficult.

@Joe, Shutter speeds has no effect. Slow or fast they will be there,
if the spacing/size and angle of the design pattern meets the camera's "criteria", it will convert it to an appropriate bluish greenish mishmash pattern or moire.

It will attract attention to itself once you do a camera move. or if the part of the scene causing this moves in the frame.

This defect will lessen a bit if you turn down sharpening in your menu.

@Charles, Thats true about getting a good monitor, whats sad is some shooters might think that checking for moire using the zoom button will let them think there is non! -its a tricky electronics when zooming in on the suspected pattern gives you clear sharp and alias free image, when in fact it only aliases and moires when zoomed back and the pattern becomes small again!

On my last project i had to film the sea and i knew moire would be a big issue. Here's the trick i used to remove it.

I masked the sea and desaturated the water to black and white. I then applied a tint filter on top of it to match the color of the sky. It worked for me so i wanted to share. I did it in Vegas but you can do this with any software.

Looks real good even in motion. Of course it's not perfect but it's a good workaround. Here are the before after pics.

Before:

http://img682.imageshack.us/img682/1754/sunsetmoire.jpg

After:

http://img64.imageshack.us/img64/1763/sunsetnomoire.jpg

You don't have to do all that, just load your clip into photoshop and use noise reduction and reduced color noise and done and will be much better like this.

Blurring the color can work too. I did that on some woodgrain that had green and red moire (the red looked okay, but the green was ugly.) After blurring the colors together, the result was very natural.