Thread: Aliasing

Page 3 of 10 FirstFirst 1234567 ... LastLast
Results 21 to 30 of 97
  1. Collapse Details
    #21
    Senior Member smelni's Avatar
    Join Date
    Apr 2005
    Location
    Manhattan
    Posts
    1,554
    Default
    why isnt there a way to create and put a real OLPF to put in front of the lens or behind the lens - If a OLPF is a physical thing and not a digital thing why isnt this possible
    SLM Production Group
    http://www.slmproduction.com - HPX500 available


     

  2. Collapse Details
    #22
    Default
    It is possible. CommanderSpike's already done a bit of a homebrew version.

    Problem is, if you eliminate all the aliasing, you're going to be left with only the true resolved detail that these cameras can provide, and that's not much more more than standard-def. It is the presence of aliasing that makes these cameras look sharp at all.

    These cameras are trying to use a still-camera sensor to do high-speed motion photography. It's beyond what they were ever designed to do. So the pixel-binning (or line skipping, whichever/whomever you believe) is necessary to get the frame rate up to video speeds. There are compromises involved. If you believe the "six-pixel bin" approach as stated by Canon's Tim Smith, each binned pixel is made up of reading a combination of six sensor pixels. But because it's a Bayer pattern sensor, thos six pixels cannot be side by side -- it's not like a 3x2 block! It's six pixels extracted out of a matrix of at least 24 (in red and blue), which means there are gaps between the pixels. Which is why spurious aliased detail "gets through". So if you put on an OLPF that's strong enough to blur those little details out, something that blurs the entire six-pixel matrix into one big pixel, you'll be left with imagery that's way way way lower than HD. But it'd be accurate.

    Which is, of course, why these cameras only resolve a medium-def image -- because, in terms of true resolving power, they can only resolve detail as small as that six-pixel bin. But if we examine that six-pixel bin as being out of a 24-pixel matrix, then that really means the OLPF would drop the resolution from the stated 18-megapixels, to 1/24 of that (which would mean a 750,000-pixel frame).

    And, guess what -- let's do the math, an SD frame has about 350,000 pixels in it, and a 720p frame has about 920,000 pixels in it. 750,000 fits right between there, doesn't it? Which is a reaffirmation of what I've been saying -- the true resolved detail on these systems is somewhere between standard-def and 720p. At best.

    Any additional "sharpness" being detected is aliasing that's leaking through and contaminating the image. (and yes, I'm well aware that people like that contamination and think it adds to the image).


     

  3. Collapse Details
    #23
    Director of Photography TimurCivan's Avatar
    Join Date
    Aug 2004
    Location
    New York City
    Posts
    12,182
    Default
    I think the bendy propeller looks AMAZING. i know its inaccurate.... but God its beautiful!
    Cinematographer
    Sigma Pro

    www.timurcivan.com 917-589-4424


     

  4. Collapse Details
    #24
    Dark Side of the Camera Postmaster's Avatar
    Join Date
    Nov 2007
    Location
    Germany
    Posts
    5,317
    Default
    Actually I don`t get it.

    Why do they use those Bayer sensors? (yeah they are cheaper)
    Why not 3 traditional chips in full size/full HD matrix and do away with all that debayer, rolling shutter, Jello, moire Voodoo Shmoodoo?

    In my book they should have phenomenal low light sensitivity and great DOF.

    To complicated? To expensive?


    Frank
    frankglencairn.wordpress.com
    http://twitter.com/FrankGlencairn



    Real men edit their films in a hex editor.


     

  5. Collapse Details
    #25
    Senior Member Al MacLeod's Avatar
    Join Date
    Feb 2008
    Posts
    884
    Default
    Manufacturers have long known that to soak the market for all it's worth, you have to appeal
    to every niche you can. If you accommodate everybody with one camera, you have wasted a lot of market potential.
    I read once that color tv availability was delayed for a time because the manufacturers wanted to fully saturate the market for black and white sets. Waste not want not!


     

  6. Collapse Details
    #26
    Senior Member adkimery's Avatar
    Join Date
    Oct 2005
    Location
    Los Angeles
    Posts
    1,648
    Default
    Quote Originally Posted by Postmaster View Post
    Actually I don`t get it.

    Why do they use those Bayer sensors? (yeah they are cheaper)
    Why not 3 traditional chips in full size/full HD matrix and do away with all that debayer, rolling shutter, Jello, moire Voodoo Shmoodoo?

    In my book they should have phenomenal low light sensitivity and great DOF.

    To complicated? To expensive?


    Frank
    Well, like Barry said these are still cameras first and foremost w/bolted on video functionality because many still photojournalists are now being asked to shoot video for the web. The fact that video people are lusting for them and trying to use them for more than what the cameras are designed for is the fault of the video people, not the camera makers.

    W/regards to 3xCCD vs 1xCMOS, AFAIK, 1xCMOS doesn't require as much space, doesn't require as much power, doesn't produce as much heat, and is overall a less expensive technology to go with. I think you also run into lens compatibility problems between camera systems that use 3xCCDs and camera systems that use 1xCMOS.


    -A


     

  7. Collapse Details
    #27
    Default
    Quote Originally Posted by Postmaster View Post
    Why do they use those Bayer sensors?
    Because sensors are monochrome. The only way to get color is to use three chips and a prism, or stick a bayer cfa in front of the chip.

    Why not 3 traditional chips in full size/full HD matrix and do away with all that debayer, rolling shutter, Jello, moire Voodoo Shmoodoo?
    Using three chips will get you away from debayering, but you'll still be subject to rolling shutter, jello, and moire.

    Rolling shutter is integral to today's CMOS video chips, and it happens whether you have one chip or three. And jello is one of the effects of rolling shutter.

    Moire is one of the most objectionable ways that aliasing manifests itself, but it's not tied inherently to Bayer filters, it's endemic to an undersampling video system.

    The reason they use one chip in these SLRs is because of the simulation of the way a film camera works. They can use the same lenses, with the same flange focal distance, with one chip. That's not possible with three chips because you have to build an optical prism assembly to split the beam of light across three chips, and that takes up space, which blows the relationship of the lens-to-chip distance, meaning those lenses won't focus properly. It's more important to them to maintain the lens relationship, than it is to avoid Bayer de-mosaic'ing.


     

  8. Collapse Details
    #28
    Junior Member
    Join Date
    Feb 2009
    Location
    CA Sacramento
    Posts
    6
    Default
    Barry great article, thanks. Too bad my 5d is such a compromise! Couldn't one bypass the compression with some software config and get the entire uncompressed sensor readout via hdmi? I was reading about some thought on that from cinema5d. Anyway I enjoyed learning and reading whY you said. I guess now I can see and agree with why the BBC won't use the 5d


     

  9. Collapse Details
    #29
    Member
    Join Date
    Jun 2004
    Location
    Panadura, Sri_Lanka
    Posts
    57
    Default
    Barry,

    What will happen if we down sample the material to SD. Will it be comparable to materials shot using a 35 mm adapter with a HD prosumer camera (EX1) and down sampled to SD.
    Maheel R Perera
    www.dcinemanetworks.com


     

  10. Collapse Details
    #30
    Senior Member
    Join Date
    Feb 2006
    Location
    Notts
    Posts
    497
    Default
    Brilliant article.

    And explains to me why the GH1 doesn't looks so good blown up on my 1080p projector, as the information just isn't there. Especially on a wide shot.

    I really didn't think it this bad though!
    RED EPIC, DRAGON, RPPS, GH5, GH4, DVX200
    DJI OSMO, PHANTOM 4 pro +, Inspire Pro 1
    www.besq.co.uk


     

Page 3 of 10 FirstFirst 1234567 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •