Rainbow-like Moire?

I'm doing some pick ups shots later today, and whilst I have the camera this morning, I decided to test this Cinema Lock Vs Canon Log, as it has confused me quote a bit, since I don't own the camera, I can't spend enough time testing it, to really find out why they do look slightly different.

I made a quick test, showing a high dynamic range light scene, with three settings; Cinema Lock, Canon Log (default Settings) and Canon Log with -10 Sharpness, black levels & black gamma adjusted (lifted). Then graded them all to look similar and it really doesn't make that much of a difference once is graded...

Also, no CA or Moire of any kind....
Shot with a Canon L 17/40 at f4, 28mm

Take a look,

 
@nuno, I think the error seen in the original post happens when its a hard high contrast edge to blowout white which I didn't see in your clip. Great clip BTW
 
I just shot some "bad case" footage where horizontals were blown out against a bright interior. Normally I wouldn't let the camera get close to this hot, but sometimes it's unavoidable (such as on transient highlights, say glints on the ocean). This is troubling. The picture of the kid's room is not cropped. The rest are crops. F2.8, 2 stops ND, 17-55 IS lens. I've seen it on the 100MM Macro too. Unfortunately adding these shots to the post made them very small but you can still make it out.

One good thing; not much of an issue when shooting fine details on the screen, moire wise. There was a tiny amount, but most people wouldn't ever see it.

Screen Shot 2012-03-12 at 4.24.24 PM.png


Screen Shot 2012-03-12 at 4.26.15 PM.png



Not-cropped.png
 

Attachments

  • Not-cropped.jpg
    Not-cropped.jpg
    16.5 KB · Views: 0
  • Screen Shot 2012-03-12 at 4.24.24 PM.jpg
    Screen Shot 2012-03-12 at 4.24.24 PM.jpg
    7.6 KB · Views: 0
  • Screen Shot 2012-03-12 at 4.25.07 PM.jpg
    Screen Shot 2012-03-12 at 4.25.07 PM.jpg
    8.2 KB · Views: 0
  • Screen Shot 2012-03-12 at 4.25.38 PM.jpg
    Screen Shot 2012-03-12 at 4.25.38 PM.jpg
    7.5 KB · Views: 0
  • Screen Shot 2012-03-12 at 4.26.15 PM.jpg
    Screen Shot 2012-03-12 at 4.26.15 PM.jpg
    6.5 KB · Views: 0
  • Screen Shot 2012-03-12 at 4.26.50 PM.jpg
    Screen Shot 2012-03-12 at 4.26.50 PM.jpg
    8.1 KB · Views: 0
Last edited:
Point noted - I hereby from this day forth pledge that I will not shoot extreme high contrast blowouts.
 
Noel Evans said:
Point noted - I hereby from this day forth pledge that I will not shoot extreme high contrast blowouts.
Click to expand...

Hahaha yes that is the point. And the camera does a pretty good job with them compared with, say, the FS100 that just fell apart. However one must be careful about transient blowouts like glints off cars/chrome, etc. If they are horizontal, it could get ugly.
 
Looks like a processing issue, to me, and not an optical issue. Maybe if it's brought to Canon's attention, we can get a firmware update that improves the performance in these scenarios.
 
Yeah, I agree, I don't think that is an optical issue myself either. Seems like some strange processing.

If I were to make a guess, I would say it's something with the highlight handling and how each channel blows out. If you look closely, you see either 1 or 2 channels completely blown out, so you see red, green, blue, cyan, yellow, magenta. Like the FS100 which tries to retain detail at the expense of shift to color, this is the same sort of thing. At those edges, it's seeing 1 or 2 channels blown, but not the third for some bizarre reason. What you'd want is the 2 or 3 channels to blow as well at the same time, (so it goes white), but that is not happening.

I also don't think it's aliasing/moire, but looks like it because of the handling of the highlight blow out. (Or should I say really, it's not aliasing in the traditional issue sense, which is because of the sensor sampling).
 
It is probably a really hard thing to do. White is perfectly desaturated where as the rolloff isn't. A high contrast edge on an angle can cause aliasing. In this case I would call it chroma aliasing. Remember blue and yellow are the same channel.
 
J Davis said:
It is probably a really hard thing to do. White is perfectly desaturated where as the rolloff isn't. A high contrast edge on an angle can cause aliasing. In this case I would call it chroma aliasing. Remember blue and yellow are the same channel.
Click to expand...

I think this is what happens when you try and retain more detail in the colors instead of using a certain portion of the dynamic range at the top for highlight protection. When I compare the blowout from the FS100 compared to the 7D, the 7D goes white as soon as any channel hits max value. There is some sort of ramp function happening to get a better roll-off (to me anyways) where each channel limits the other channels.

With the FS100, this is not the case. If a single (or two) channels goes to clip, it doesn't bring the third channel up (or other two channels). What happens is you end up getting more detail, but you get a colored blowout at that color.

It's definitely bizarre.

Definitely something I would share with Canon.
 
J Davis said:
op's looks like need creatives on 'roids. Sharpening?
Click to expand...

Yeah, and I really tried hard to create a problem. I had to intentionally over expose, Way over expose anything I would normally do with the camera. So while it's possible to make this error come about, it's also possible to make it a lot worse by intentionally blowing out your backgrounds. I'm not sure how the original poster got it to look that bad, I've never been able to do that in a normal shooting situation where you ensure that your whites don't go off the waveform.
 
I'm sharing issue with Canon. But I got some good advice which I concurred with today. A good camera op I know said the answer is easy, expose for your brightest highlight. Use the waveform, and/or zebras, ensure that. If your shadows go dark, just bring them up in post as long as they're not too crushed in the field. Clipping causes all kinds of problems. And this camera it happens to cause chroma aliasing on horizontals. On the FS 100, the camera just laughs at you. It's a lot worse there, can happen on verticals as well, and it's much harder to control just using the histogram. In both cases, if you keep your highlights controlled, this problem shouldn't show itself. That's probably why I never noticed it before, and I've shot or produced a fair amount on the camera since I got it.
 
I believe that lensing is also very important, a good lens will dramatically reduce flare, the more the elements, the better the flare control. When not controlled, flare degrades an image a lot, and these examples are, I believe mainly a product of lens flare.

I don't have one with me, but I believe a polarizer would greatly reduce that kind of destructive chroma aliasing.

Just sayin'...
 
re: expose to protect highlights. you can't always apply that rule, let say you were shooting people on a white back ground, sharp and in-focus and someone had dark hair
 
Last edited:
Nuno Dias said:
Use fill light.
Click to expand...

I'm sorry but I don't understand your reply at all. :) The problem of this chroma aliasing is when you have a high contrast edge to blowout white. If I'm shooting someone with dark hair on a white background how would fill light help? If anything I would under expose so the white bg can be lifted in post but you don;t want to have to do that if you are handing the client the media and you are not involved in post
 
I meant in a way that i you avoid that high contrast so that the sensor won't pick up the chroma aliasing, by bouncing a small amount of fill light in her hair, in post you can bring it down to shadow if you want.

But if you don't want to hand over that 'unfinished' shot to the client, you can do as the poster suggested, expose your brightest light to just below peeking (so that it won't create the highlight aliasing) and expose her hair accordingly to achieve the shadow you want.

That would work.
 
FWIW Canon EOS Support said they have never heard of this problem before. They want to see the camera but I suggested they try a similar shot on their own; they'll see it.

Nuno, all the EF lenses I have can show the highlight aliasing on angles and horizontals to some degree if the whites are overexposed, cheap to expensive (e.g. Canon 70-200 F2.8 IS II). I think I never noticed this before it was reported to me because, well, I never clipped the whites past 100 intentionally (as I did in the test). And I saw no signs of the issue where whites were clipped necessarily (for example, shooting into the sun with branches of a tree in front of it). IN fact, most of the places where the FS100 showed a really bad chroma aliasing on contrasted highlights, the C300 shows nothing or very little. I had to really look to see it.

This issue happens very infrequently if properly exposed and set up but it is one to look out for. I'm surprised that the OP saw it so bad, as have some others.
 
Last edited:
You must log in or register to reply here.
Back
Top