Noise in green foliage

[Barry Green]

I think what you were seeing in the foliage is likely "mosquito noise", a JPEG/DV/DCT type of compression artifact. Especially if lowering the detail/sharpening made the noise go away.

DCT algorithms at relatively high compression ratios don't like fine-detail high-contrast edges, and grass/leaves provides LOTS of fine-detail high-contrast edges. So lowering the sharpness can help to minimize the introduction of mosquito noise.

As A.J. said, if the noise pattern is moving, it's electronic noise. If the pattern is stationary when shooting a stationary object, it's more likely compression artifacts.

[Shekar Dattatri]

Thanks, guys, for the great feedback, I will keep you posted.

[Kevin Kocak]

So basically, the Xl2 is a great camera... as long as you don't shoot anything with a lot of grass or trees.
I am saying that sincerely. At first I was very upset about this but because of the quality of the Xl2 in many other scenarios I am accepting it. If all you are going to be shooting is grass and trees then you might want to investigate other options.

[Rachel Oliver]

Hi;

Aghhh! Don't say stuff like that, I'm about to shoot a short in a rural English landscape full of wide angle green stuff and it was my call to use the XL2! I'm going with the "it's the limitations of the format, not the camera" suggestion. Seriously though it's interesting and I'll be watching out for any trouble in my tests.....

Olly

[Stefan Scherperel]

Hey can anybody post a little clip of this problem? I really have yet to see anything that would say that this camera cannot be used to shoot greens. That just doesn't make sense.

[Kevin Kocak]

I have no way to post my footage at the moment but believe me it is a problem. I went several rounds with a DP over this. When we had our problem it was like this. We had the Xl2 mounted on a jib. We were shhoting basically a rich green garden outside of a house. There was a lot of bright green grass, trees, and shrubs around the house. When the camera was stationary no problems. When we made our camera move, a descending diagonal movement the grass, and the leaves looked like they were dancing. Small, blocky, artifacts all over them. As soon as the camera stopped they disappeared. We tried many things and eventually scrapped the shot.

[Stefan Scherperel]

and this was only in the greens?
Hmmm, if it is just when you move then that would definatly be a moir effect like barry explained. However, what were you using to view the footage? Did you have a full res 16:9 monitor? have you viewed it on the computer screen?
IF it flickers on the hi res monitor and computer screen then there is a bigger problem because this would not be an issue with resolution rather something else. I really wish I could help. If you want to email me a small clip, under 10 megs, let me know, I can host it for you on my server.

[Kevin Kocak]

It was primarily on the greens. There was some artifacting on the roof as well. I was not on set at the moment when it was recorded. The camera crew was using a small NTSC field monitor. No need for 16:9, we were shooting 4:3 in 60i. I have noticed since then that the camera has a lot of problems with moire or artifacting or whatever you want to call it. Over the last 2 weeks I have been working on a project where we shot one weekend with a DVX100 and the next week with our Xl2. Both in the same soundstage with the same lights on the exact same set. The DVX image was very warm and soft and oversaturated. The Xl2 is very cold and sharp. There were several areas where we picked up moires on the Xl2 which were not there when we shot with the DVX. Please don't take this as a DVX vs Xl2 post because it isn't. I like the Xl2 much better. I am just saying that the camera seems to have more issues with moire patterns and they are very pronounced outdoors in grassy areas or dense foliage.

[A. J. deLange]

Kevin said the magic word" "blocky". This means that what he is seeing is definitely DCT related and is caused by the mechanism I explained (or tried to anyway) last week. At http://homepage.mac.com/ajdel/FileSharing5.html there is some video the first clip of which shows pinwheels spinning in the breeze. If you go through this a frame at a time you will see this effect clearly especially on the edges of the pinwheels' blades. They appear serrated. The only way to eliminate this is to cut down on detail especially in the green (detail in Y-B and Y-R is cut down for you when these signals are formed). Green (or Y which is mostly green) is the detail carrying channel.

[Kevin Kocak]

Cut down how??? I have heard so many explanations of this now but no definite solutions. So I said blocky what difference does it make. It is there and the footage is useless. And I am not saying you can't shoot in those circumstances but rather be prepared for what you may encounter. Like I said many times before I love this camera but it does have limitations. I am just sharing my experience with it so that maybe it can help us all figure this out. Right now I don't see a solution only everybody explaining the problem so maybe we are getting closer here. I am editing another project right this second but I will try to email some footage to the person who said they would host it. And, by the way, the regional Canon rep here refered to it as aliasing. I don't care what you call it, it sucks.

[A. J. deLange]

It makes a difference because it tells me what's causing it and what I might be able to do about it. Blocky artifacts come from the DCT compression used by DV - not aliasing. As such it's not a limitation of the camera unless you want to call it a limitation of the camera in the sense that the camera can supply more information, in some circumstances, to the DV25 algortithms than the DV25 algorithms can handle or in that the camera uses the DV25 algoritms. To get rid of this artifacting you must limit the amount of high frequency content presented to the algorithms. This can be done by limiting the relative size of "busy" portions of the picture relative to the whole. Recompose to eliminate large expanses of grass or trees or anything else with lots of fine detail especially if it is green. There are limitations as to the extent this can be done especially in terms of constraining the creative freedom of the photographer but then there are plenty of other constraints as well. Another way, the way taken by the DVX100 apparently, is to implement an optical system with lower resolution i.e. "soft" lens with lower resolution CCD. You can acheive this result by using soft lenses for shots which have lots of busy content or by using a softening filter. Another way to lower high frequency content is to get far enough away from the high frequency stuff that even the Canon lenses blur it relative to the pixel size.

I don't think there is a "solution". This is a limitation of DV. Your experiences and those of others are of benefit because they help everyone better understand what the limitations of this camera are.

[Kevin Kocak]

Well put AJ. After reviewing my previous post it seemed a bit confrontational which is not where I was trying to go there. I am always having to defend this camera and have gotten tired of doing so. I now tell people to take it for what it is and choose a camera that best suits their needs. Anywho thanx for the explanation and advice. As always very helpful.

[Rob Lohman]

What software is available for editing? You could try adding a
chroma blur filter, see what that does to the "green" footage.

[Kevin Kocak]

I use FCP. That's an excellant idea.