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> If you work with image kernels / reconstruction filters long enough you will eventually learn that 90% of the time you want a gauss kernel. Strongly disagree

> If you work with image kernels / reconstruction filters long enough you will eventually learn that 90% of the time you want a gauss kernel. Strongly disagree, and my commercial software is known for its high image quality and antialiasing. Gaussian is way too blurry unless you're rendering for film.

CyberDildonics 2y ago
Then your filter width is too wide. Try 2.2 - 2.5
dahart 2y ago
In my film experience, I think most film people don’t like Gaussian either; too blurry for them as well. At least, I’ve sat in on filter evaluations with a couple of directors & VFX sups many years ago, and they said Gaussian was too soft and preferred a sharper Mitchell. But I am curious, perhaps similar to the sibling comment - how do you determine the optimal Gaussian width? You can certainly go narrower/sharper and get less blur at the cost of more artifacts similar to a sharper filter, right? BTW have we discussed this recently? ;) I love Gaussian’s ability to hide any hint of the pixel grid, which I find very few filters can do. I also tend to believe that, perceptually speaking, over-blurring slightly doesn’t hurt while under-blurring does, especially for moving things, but that might be more personal bias than objective reality. I would be interested to look at any comparisons or results from your software or in general, if you have some.
- CyberDildonics 2y ago
  The truth is that when people test out filters they are looking close up at the pixels, trying to squeeze out detail, but the reality is that whatever minute detail might get slightly softened by a 2.2-2.5 gauss filter will get chewed up by the process of color correction and compression anyway. The aliasing you can end up with from a mitchell filter though can be noticeable all through the process. Not only that, but what will the compositor do when they see the aliasing? They'll blur it. Basically it is trying to squeeze blood from a stone and the image out of renderer is going to be far sharper than anyone will see because it will go through multiple stages. Even compositing almost never leaves a render verbatim. There is usually some sort of slight softening, chromatic aberration, lens distortion and/or other transforms that require resampling anyway. It is picking up pennies in front of a bulldozer and only causes problems to have a filter that's too sharp, let alone one that has negative lobes.
  - dahart 2y ago
    Oh FWIW, the sessions I remember most vividly were for the first Shrek movie, which was printed to actual film, projected to a theater screen, and final render was at slightly lower than 1080p resolution. The digitizing to film does add a little blur, of course, but not a lot since the resolution was so low and the pixels so big. The filter did kinda matter, and the compositors did not add extra blur in this case. I was highly impressed with how sensitive the director and lighting/fx supes were to filter differences, and how quickly they could spot them in animated clips that were often less than one second long. The main thing they were doing was trying to avoid texture sizzle without overblurring.
    - CyberDildonics 2y ago
      The digitizing to film Scanning film would be digitizing it, going out to film could be called printing. does add a little blur A lot of blur. 35mm film had a lot of folk wisdom built up around it and even though it would be scanned and worked on at 2k resolution for live action vfx, if you actually zoomed in it would be extremely soft. You could get away with 1.5k just for printing to the first generation film, let alone the 2nd gen master prints and the third gen prints that went out to theaters. The filter did kinda matter It is extremely unlikely lighters were changing the actual pixel sample filters on a shot by shot basis. This is something that is set globally. Also if you set it differently for different passes and you use holdouts, your CG will not line up with the other CG renders and you will get edges from the compositing algebra not being exact. I was highly impressed with how sensitive the director and lighting/fx supes were to filter differences, No one is changing the pixel sampling filters on a shot by shot basis and no one is going to be able to tell the filter just by looking at playing back on film. This is simply not reality. and how quickly they could spot them in animated clips that were often less than one second long Absolutely not. Whatever you are talking about is not different pixel sample filters. Aliasing in general yes, but that's much more complex. The main thing they were doing was trying to avoid texture sizzle without overblurring. This has nothing to do with the renderer's pixel sample filters which is what would be the only analog to the article here. Maybe you are talking about texture filtering, although that is not a difficult problem due to mipmapping and summed area mapping. Even back then a geforce 2 could do great texture filtering in real time. Maybe you are talking about large filter sizes in shadow maps, which need a lot of samples when using percentage closer filtering, but that has nothing to do with this.
- a_e_k 2y ago
  Historically, Pixar's RenderMan defaulted to a 2x2 Gaussian filter [1], and from what I can see, that hasn't changed [2]. Essentially it uses a truncated isotropic (non-separable) Gaussian defined by exp(-2.0 * (x*x + y*y)) with a 2x2 pixel support [3], which is slightly soft and completely avoids ringing. Gaussian also plays very nicely with filtered importance sampling [4] since it has no negative lobes. (Though I remember a number of studios using RenderMan preferring filters with a bit of sharpening.) [1] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 [2] https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering [3] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=207 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=20... [4] https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=d5d120ae2c47e38fc4a2d379cfcf9953f5e23ada https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&d...
  - dahart 2y ago
    Oh very interesting, thanks! Yeah I guess the PDI folks wanted the benefits without the slightly soft part, but I stand corrected, not all film people are the same.

CyberDildonics 2y ago

Then your filter width is too wide. Try 2.2 - 2.5

dahart 2y ago

In my film experience, I think most film people don’t like Gaussian either; too blurry for them as well. At least, I’ve sat in on filter evaluations with a couple of directors & VFX sups many years ago, and they said Gaussian was too soft and preferred a sharper Mitchell. But I am curious, perhaps similar to the sibling comment - how do you determine the optimal Gaussian width? You can certainly go narrower/sharper and get less blur at the cost of more artifacts similar to a sharper filter, right? BTW have we discussed this recently? ;) I love Gaussian’s ability to hide any hint of the pixel grid, which I find very few filters can do. I also tend to believe that, perceptually speaking, over-blurring slightly doesn’t hurt while under-blurring does, especially for moving things, but that might be more personal bias than objective reality. I would be interested to look at any comparisons or results from your software or in general, if you have some.

CyberDildonics 2y ago
The truth is that when people test out filters they are looking close up at the pixels, trying to squeeze out detail, but the reality is that whatever minute detail might get slightly softened by a 2.2-2.5 gauss filter will get chewed up by the process of color correction and compression anyway. The aliasing you can end up with from a mitchell filter though can be noticeable all through the process. Not only that, but what will the compositor do when they see the aliasing? They'll blur it. Basically it is trying to squeeze blood from a stone and the image out of renderer is going to be far sharper than anyone will see because it will go through multiple stages. Even compositing almost never leaves a render verbatim. There is usually some sort of slight softening, chromatic aberration, lens distortion and/or other transforms that require resampling anyway. It is picking up pennies in front of a bulldozer and only causes problems to have a filter that's too sharp, let alone one that has negative lobes.
- dahart 2y ago
  Oh FWIW, the sessions I remember most vividly were for the first Shrek movie, which was printed to actual film, projected to a theater screen, and final render was at slightly lower than 1080p resolution. The digitizing to film does add a little blur, of course, but not a lot since the resolution was so low and the pixels so big. The filter did kinda matter, and the compositors did not add extra blur in this case. I was highly impressed with how sensitive the director and lighting/fx supes were to filter differences, and how quickly they could spot them in animated clips that were often less than one second long. The main thing they were doing was trying to avoid texture sizzle without overblurring.
  - CyberDildonics 2y ago
    The digitizing to film Scanning film would be digitizing it, going out to film could be called printing. does add a little blur A lot of blur. 35mm film had a lot of folk wisdom built up around it and even though it would be scanned and worked on at 2k resolution for live action vfx, if you actually zoomed in it would be extremely soft. You could get away with 1.5k just for printing to the first generation film, let alone the 2nd gen master prints and the third gen prints that went out to theaters. The filter did kinda matter It is extremely unlikely lighters were changing the actual pixel sample filters on a shot by shot basis. This is something that is set globally. Also if you set it differently for different passes and you use holdouts, your CG will not line up with the other CG renders and you will get edges from the compositing algebra not being exact. I was highly impressed with how sensitive the director and lighting/fx supes were to filter differences, No one is changing the pixel sampling filters on a shot by shot basis and no one is going to be able to tell the filter just by looking at playing back on film. This is simply not reality. and how quickly they could spot them in animated clips that were often less than one second long Absolutely not. Whatever you are talking about is not different pixel sample filters. Aliasing in general yes, but that's much more complex. The main thing they were doing was trying to avoid texture sizzle without overblurring. This has nothing to do with the renderer's pixel sample filters which is what would be the only analog to the article here. Maybe you are talking about texture filtering, although that is not a difficult problem due to mipmapping and summed area mapping. Even back then a geforce 2 could do great texture filtering in real time. Maybe you are talking about large filter sizes in shadow maps, which need a lot of samples when using percentage closer filtering, but that has nothing to do with this.
a_e_k 2y ago
Historically, Pixar's RenderMan defaulted to a 2x2 Gaussian filter [1], and from what I can see, that hasn't changed [2]. Essentially it uses a truncated isotropic (non-separable) Gaussian defined by exp(-2.0 * (x*x + y*y)) with a 2x2 pixel support [3], which is slightly soft and completely avoids ringing. Gaussian also plays very nicely with filtered importance sampling [4] since it has no negative lobes. (Though I remember a number of studios using RenderMan preferring filters with a bit of sharpening.) [1] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=40 [2] https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering https://rmanwiki-26.pixar.com/space/REN26/19661819/Filtering [3] https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=207 https://paulbourke.net/dataformats/rib/RISpec3_2.pdf#page=20... [4] https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=d5d120ae2c47e38fc4a2d379cfcf9953f5e23ada https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&d...
- dahart 2y ago
  Oh very interesting, thanks! Yeah I guess the PDI folks wanted the benefits without the slightly soft part, but I stand corrected, not all film people are the same.