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Technical question about Iray noise

Member_257874Member_257874 Posts: 76
edited August 2017 in Technical Help (nuts n bolts)

Hello

When testing with low quality renderings in a movie I noticed that the noise, Iray produces because of it's sampling, always stays in the same place. So it's not like static noise on an analogue TV screen that wizzles around but it looks like every picture is sampled with the same "seed" value. Why is it this way? I thought Iray takes light rays and randomly reflects them from surfaces until they hit a light source (or don't where the sample will return "black") or did I understand something wrong here? And couldn't be image quality improved a little, when the seed of the random changes each iteration so one get's a greater variance in random samples (mean's one get's a greater chance to render a pixel with the correct light souce instead of missing it into dark infinity)?

Post edited by Member_257874 on

Comments

  • ToborTobor Posts: 2,300

    What you're seeing is not noise, and it's not random. These are unconverged pixels. The process involves sending light rays throughout the scene in a predictable process, and sampling the endpoints as the pixels in the image. There must be numerous samples to each pixel (hundreds to thousands) before Iray can determine that the sampling is correct. All this follows a set algorithm. While there may be elements of the algorithm that could provide a different distribution, these settings are not user customizable. Some users have reported that making very small changes in the scene can produce a different distribution, though how well the separate images can be combined is a matter of whatever filtering tools you might have at your disposal .

  • designerendesigneren Posts: 1
    Surely a renderer like Iray must have some kind of way to randomize the seed value? I have this very same problem. I do not mind the noice iray produces. It is quite nice, once you add some love to it, but as long as the algoritm that distributes the sample-rays uses the same seed for every frame then that really hurts daz studio as an animation tool. If anyone with knowledge about the Iray-renderer reads this, please let us know if there is a way to scriptfix this.
  • mindsongmindsong Posts: 1,715

    I'll second that re-request. It makes animations look like a screen is in front of the camera, rather than random TV-like noise. I'd really prefer the more random effect too.

    Any experts with some ideas or workaround theories?

    tia,

    --ms

  • kenshaw011267kenshaw011267 Posts: 3,805

    Iray just doesn't work the way you guys imagine. There is no random seed not is there any way to add one. If your renders end with too many unconverged pixels then you need to add more light or to let the render run for longer.

  • algovincianalgovincian Posts: 2,636
    kenshaw011267 said:

    Iray just doesn't work the way you guys imagine. There is no random seed not is there any way to add one. If your renders end with too many unconverged pixels then you need to add more light or to let the render run for longer.

    Are you certain about that? Iray interactive uses a quasi Monte Carlo approach.

    - Greg

     

  • kenshaw011267kenshaw011267 Posts: 3,805

    No idea where you got that from. I've seen multiple statements by iray devs that the renders are deterministic and that unchanged starting conditions will always result in the same render including the same unconverged pixels. If there was a pseudo random element that wouldn't be the case.

  • algovincianalgovincian Posts: 2,636
    kenshaw011267 said:

    No idea where you got that from. I've seen multiple statements by iray devs that the renders are deterministic and that unchanged starting conditions will always result in the same render including the same unconverged pixels. If there was a pseudo random element that wouldn't be the case.

    Got it from nVidia themselves:

    Iray Interactive now incorporates a new and unique approach to image sampling that speeds up the incremental refinement of an image by a factor of 10. This patent-pending approach uses the Quasi Monte Carlo (QMC) method to ensure high-quality imagery and efficient, fast rendering and Path Space Filtering (PSF) to reduce image noise.

     

    https://developer.nvidia.com/sites/default/files/akamai/designworks/docs/nvidia_iray_overview.150810.A4.pdf

    My gut tells me that the “predictive” nature of the AI being used are what makes the output not appear random.

    - Greg

  • kenshaw011267kenshaw011267 Posts: 3,805

    Had to do some research as this isn't my field, quasi Monte Carlo doesn't use pseudo random numbers. That's why it's called quasi. It definitely is deterministic and has no random element. 

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