Thread: AA Filter

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  1. #1 AA Filter 
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    Here is a great article by Barry Green about aliasing from dvxuser
    http://www.dvxuser.com/articles/article.php/20/

    he wrote " Can you combat aliasing? Is there anything you can do to prevent it? Well, it basically comes down to focus since only the finest detail causes aliasing, throwing it out of focus will prevent aliasing. Soft focus eliminates fine detail. You can try a couple of things, such as defocusing slightly on shots where aliasing is showing itself. By defocusing, you change the amount of detail present in the shot and you add a natural blur, which means you're kind of inventing your own video-appropriate OLPF, right? You can also try a softening filter on the front of your lens, to see if that will take the false detail away and leave only the true sample-able detail. But be aware, if you took all the false detail out, you'll be left with a camera that's capable of barely better than standard-def imaging! The true resolving capability of these cameras is shown on the resolution charts, and the only reason they look high-def at all is because of the presence of the false detail, so you don't necessarily want to filter it all out, you really just want to get rid of the stuff that is obviously wrong. Frame it out, or open the iris to throw the offending background detail more out of focus, or consider using something like a Caprock anti-moire filter or a diffusion filter on the front of your lens. I'll update this article with the effectiveness of some of these methods as I have a chance to test them with various HDSLRs. "
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  2. #2  
    Senior Member Peter J. DeCrescenzo's Avatar
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    Quote Originally Posted by Barry Green View Post
    http://www.bmcuser.com/showthread.ph...ll=1#post14054
    ... Perhaps there's something being lost in the communication here. ...
    I have a small hope this is the case, and that the BMCC will actually ship with a OLPF tuned for 2.5K & 1080p video.

    However, if it doesn't, here are a few things we know:

    The BMCC is designed to record 2.5K & HD motion video (and not hi-res stills) that look at least as good as what John Brawley has shown us thus far.

    And, because the BMCC is designed for motion video, not stills, unlike a DSLR there's no penalty for adding a 3rd party after-market OLPF if necessary, other than the not inconsiderable issues of cost & availability. You typically won't need to repeatedly insert & remove the filter as is the case with a DSLR used for shooting both video and stills (an add-on OLPF blurs MP stills too much). With the BMCC you'd likely install the OLPF once and leave it in place.

    Given the BMCC's likely popularity, if it doesn't include a OLPF, and if its video frequently suffers as a result, my guess is that Mosaic and others (perhaps BMD?) will offer one at a reasonable price ASAP.


    [I moved my post from the Shipping Status thread to this one.]
    Last edited by Peter J. DeCrescenzo; 08-14-2012 at 07:49 PM.
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  3. #3  
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    The wheel on the big screen still turning backward but Movie goers still going to the movies for 100 years, I would like my camera without a permanent AA filter, I can add it later if I need to.
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  4. #4  
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    So correct me if I'm wrong. As long as the output resolution matches the number of photo cells on the sensor no AA filter is needed, correct? If this is the case, than the BMCC will only have the aliasing issues in ProRes and DNxHD, RAW 2.5K wouldn't have the issue correct?
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  5. #5  
    I guess I can show you my screen shots. 100% vs 300%. In 100%, the aliasing does not move, shimmer or rainbow. I'm satisfied and I'm a pixel peeper. But, it is there.



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  6. #6  
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    Quote Originally Posted by rawCAM35 View Post
    The wheel on the big screen still turning backward but Movie goers still going to the movies for 100 years, I would like my camera without a permanent AA filter, I can add it later if I need to.
    Quote Originally Posted by mattbatt View Post
    I guess I can show you my screen shots. 100% vs 300%. In 100%, the aliasing does not move, shimmer or rainbow. I'm satisfied and I'm a pixel peeper. But, it is there.



    It might be a good thing to note that this was from ProRes footage.
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  7. #7  
    Senior Member AndrewDeme's Avatar
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    Quote Originally Posted by mattbatt View Post
    I guess I can show you my screen shots. 100% vs 300%. In 100%, the aliasing does not move, shimmer or rainbow. I'm satisfied and I'm a pixel peeper. But, it is there.
    Am curious what you think.....do you reckon when these sorts of scenes are filmed in RAW that this is what they will look like or do you think this is a result of compression (either in or out of camera).
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  8. #8  
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    Quote Originally Posted by Brian@202020 View Post
    So correct me if I'm wrong. As long as the output resolution matches the number of photo cells on the sensor no AA filter is needed, correct? If this is the case, than the BMCC will only have the aliasing issues in ProRes and DNxHD, RAW 2.5K wouldn't have the issue correct?
    I'd like to know that too.
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  9. #9  
    Senior Member Peter J. DeCrescenzo's Avatar
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    It's worth noting that only a portion of one of the frames is enlarged in the posts above. And that it was compressed by Vimeo from whatever compressed file JB uploaded. So, a crop of a frame that was compressed at least 3 separate times (including the cam's in-camera ProRes compression).

    Unfortunately, BMCuser.com reduces large images down to 1000 pixels wide. I'm not saying the aliasing and color weirdness isn't there, but that it doesn't look too bad on my 1920 x 1200 pixel laptop screen, and looks even better on my 1080p HDTV.

    I'm hopeful aliasing isn't a common problem in ProRes BMCC footage, because that's the format I plan to use most of the time. Looking forward to learning more ...

    bmcc alleged aliasing 1.jpg
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  10. #10  
    Senior Member nickjbedford's Avatar
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    To tell you the truth, it's good to know that this can be found in footage, but I was honestly never even close to perceiving it when watching the footage, and I'm not a layman. I was too busy focusing on the parts John was shooting for us to see, which are the actors then brief glances at the environment.

    At 24-25fps, and with cuts every 1-3 seconds, your audience is far less likely to notice it. And the issue with the computer chair in the previous Pool Shark footage wasn't even because of the sensor, but a naturally occurring visual phenomenon.

    You probably just use a tiny window with a desaturate/slight blur to reduce it in post, but it's more likely that you'll not even notice it until you're looking at individual frames for minutes on end in Resolve.
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