5 ms·

Depth of field blur: the Swiss army knife that improved the framerate

111 points by exch 15y ago

timmorgan 15y ago
Pet peeve, It's "farther."
- StavrosK 15y ago
  "Farther away", but "improved even further". I know this is what you mean, but others might get confused.
  - timmorgan 15y ago
    Indeed, thank you.
  - _delirium 15y ago
    I don't think there's a consistent distinction on those. The OED lists greater-distance meanings for both words, and has quotations going back centuries for both (Shakespeare used "further" for distance). Spot-checking on Google Books, it looks like "further away" and "farther away" have roughly equal contemporary usage, as well.
    - StavrosK 15y ago
      Hmm, that's true. I use them in the way previously described, but don't correct people on it, as it's too late for that. We can still save "it's/its" "their/there/they're" and "your/you're", though!
      - evincarofautumn 15y ago
        This is wildly off-topic, but here goes. We really can’t; you’re going to have to accept one day that your position is untenable. Where languages evolve, we’re powerless to prevent their inexorable transformation. They’re like species—there’s no such thing as “devolution”. Some would that it were different—they say “we could’ve won, if only”. Try though we might, the globalising power of the Internet, and its effect on communication, mean that it’s ultimately futile to fight change—even when it makes us uncomfortable. We really cant, your gonna hafta accept one day that your position is untenable. Were languages evolve, were powerless to prevent there inexorable transformation. There like species, theres no such thing as “devolution”. Some would that it were different—they say “we could of won, if only”. Try tho we might, the globalising power of the internet, and its effect on communication, mean that its ultimately futile to fight change, even when it makes us uncomfterble.
        yew 15y ago
        I consider loss of specificity (which is what is happening in the latter case) to be devolution, and do not find descriptivism a convincing (or even meaningful) argument against that position. Other arguments might prove more successful, of course. As for futility - well, we'll see, won't we? As you say, though, this is wildly off topic.
        hej 15y ago
        There are two contradictory forces shaping a language: effectiveness and clarity. Languages walk the narrow path between those two. Sometimes languages move in one direction, sometimes in the other direction. A loss of specificity (like the disappearing distinction between “it’s” and “its”) increases effectiveness (for the writer) at the cost of clarity. I’m not sure with what justification you can call that devolution. It’s a change that affects clarity only minimally: There aren’t many situations where using “it’s” instead of “its” is confusing and doesn’t communicate what the writer wants to communicate. It just makes sense that every flourish in a language that adds rarely needed specificity will be ground away with time. Stylistically you are certainly within your rights to call it a devolution (I also don’t like it aesthetically), but that’s very subjective. I don’t think that pointing at specificity is the way to go here, though.
        _delirium 15y ago
        One of the fascinating general trends in that respect, which I don't think the reasons for are fully settled yet, is the tendency of languages to simplify grammar over time. Ancient Greek and Latin had more complex grammatical features than modern Greek and Italian do, for example, and similarly with Sanskrit and its descendants. Of course, it can't be a universal trend, because the complexity must have arisen at some point as well.
        twelvechairs 15y ago
        English dropped grammatical gender some centuries ago. Despite being 'less specific' in some ways, I'm not sure too many would argue that this was a step backward.
      - _delirium 15y ago
        If anything, I think this one is going the other way: traditionally there wasn't a distinction, but one seems to be emerging more recently.
- vilhelm_s 15y ago
  My understanding is that "further" and "farther" can be used interchangeably when talking about distances (so "further" can be used wherever "farther" can, but not the other way around). This is for example what the usage note at http://www.merriam-webster.com/dictionary/farther http://www.merriam-webster.com/dictionary/farther says, although they state that the usage is becoming more polarized.
janzer 15y ago
My first thought on reading is this is essentially (at least in spirit) mipmapping[1] applied to his 2D (2.5D?) engine. 1. http://en.wikipedia.org/wiki/Mipmap http://en.wikipedia.org/wiki/Mipmap
daenz 15y ago
Downsampling images before a blur seems to be a pretty standard technique to get more perceived bang (blur) for your buck. If you don't downsample the image too far, the blur adequately covers any artifacts the downsampling (and re-scaling) would have. The result is, an N radius blur can be stretched a lot farther, because the downsampling (and re-scaling) itself adds an blur of its own. This performance optimization doesn't really work for variable-width blurs (like depth of field) on 3d scenes though, because some parts of your image need to be crisp, while others blurred. Downsampling the entire image would lose resolution on the crisp parts. 3d depth of field blurs are actually pretty interesting though. They're variable width, which is just another way of saying that each pixel on the final image might be blurrier or less blurry than another pixel. Implementing this kind of variable blurring is a tough task, and typically done by scaling up or scaling down a disk of random sampling coordinates for each pixel. When the disk of coordinates is large, the sampling coordinates sample further from the pixel its centered on, so the resulting pixel has a bigger blur. When the sampling disk is small, the surrounding coordinates are closer to the center pixel, creating a smaller blur. The size of this sampling disk is controlled by the depth of the pixel from the near and far focus planes of the virtual camera. I've glossed over a lot (like the artifacts that can result from 3d DoF), but Nvidia's GPU gems has a great article on the subject http://http.developer.nvidia.com/GPUGems3/gpugems3_ch28.html http://http.developer.nvidia.com/GPUGems3/gpugems3_ch28.html
- Retric 15y ago
  In 3D games with significant view distance, they often use low resolution copy's for displaying distant objects. These low resolution copy's are progressively replaced with ever more complex versions as you approach. I suspect you could mix in some blur to get a smoother transition and enable even lower resolution copy's while avoiding the 'pop' that occurs when you suddenly get the high rez version of an object.
- mrhyperpenguin 15y ago
  > This performance optimization doesn't really work for variable-width blurs... An alternative would be to use Summed-area tables [1] where each texel contains the sum of all texels that are above and to the left of the current texel. This allows variable-width blurs to be computed in constant time, using only four texture samples (!). And the concept of a variable-width blur is an approximation to a related concept in photography/optics called the "circle of confusion." [2] The circle of confusion, combined with bokeh sprites, are usually what AAA games are doing for depth of field [3]. See [4] for more details. [1] http://http.developer.nvidia.com/GPUGems3/gpugems3_ch08.html http://http.developer.nvidia.com/GPUGems3/gpugems3_ch08.html [2] http://en.wikipedia.org/wiki/Circle_of_confusion http://en.wikipedia.org/wiki/Circle_of_confusion [3] http://udn.epicgames.com/Three/BokehDepthOfField.html http://udn.epicgames.com/Three/BokehDepthOfField.html [4] http://mynameismjp.wordpress.com/2011/02/28/bokeh/ http://mynameismjp.wordpress.com/2011/02/28/bokeh/

111 points by exch 15y ago

timmorgan 15y ago

Pet peeve, It's "farther."

StavrosK 15y ago
"Farther away", but "improved even further". I know this is what you mean, but others might get confused.
- timmorgan 15y ago
  Indeed, thank you.
- _delirium 15y ago
  I don't think there's a consistent distinction on those. The OED lists greater-distance meanings for both words, and has quotations going back centuries for both (Shakespeare used "further" for distance). Spot-checking on Google Books, it looks like "further away" and "farther away" have roughly equal contemporary usage, as well.
  - StavrosK 15y ago
    Hmm, that's true. I use them in the way previously described, but don't correct people on it, as it's too late for that. We can still save "it's/its" "their/there/they're" and "your/you're", though!
    - evincarofautumn 15y ago
      This is wildly off-topic, but here goes. We really can’t; you’re going to have to accept one day that your position is untenable. Where languages evolve, we’re powerless to prevent their inexorable transformation. They’re like species—there’s no such thing as “devolution”. Some would that it were different—they say “we could’ve won, if only”. Try though we might, the globalising power of the Internet, and its effect on communication, mean that it’s ultimately futile to fight change—even when it makes us uncomfortable. We really cant, your gonna hafta accept one day that your position is untenable. Were languages evolve, were powerless to prevent there inexorable transformation. There like species, theres no such thing as “devolution”. Some would that it were different—they say “we could of won, if only”. Try tho we might, the globalising power of the internet, and its effect on communication, mean that its ultimately futile to fight change, even when it makes us uncomfterble.
      - yew 15y ago
        I consider loss of specificity (which is what is happening in the latter case) to be devolution, and do not find descriptivism a convincing (or even meaningful) argument against that position. Other arguments might prove more successful, of course. As for futility - well, we'll see, won't we? As you say, though, this is wildly off topic.
        hej 15y ago
        There are two contradictory forces shaping a language: effectiveness and clarity. Languages walk the narrow path between those two. Sometimes languages move in one direction, sometimes in the other direction. A loss of specificity (like the disappearing distinction between “it’s” and “its”) increases effectiveness (for the writer) at the cost of clarity. I’m not sure with what justification you can call that devolution. It’s a change that affects clarity only minimally: There aren’t many situations where using “it’s” instead of “its” is confusing and doesn’t communicate what the writer wants to communicate. It just makes sense that every flourish in a language that adds rarely needed specificity will be ground away with time. Stylistically you are certainly within your rights to call it a devolution (I also don’t like it aesthetically), but that’s very subjective. I don’t think that pointing at specificity is the way to go here, though.
        _delirium 15y ago
        One of the fascinating general trends in that respect, which I don't think the reasons for are fully settled yet, is the tendency of languages to simplify grammar over time. Ancient Greek and Latin had more complex grammatical features than modern Greek and Italian do, for example, and similarly with Sanskrit and its descendants. Of course, it can't be a universal trend, because the complexity must have arisen at some point as well.
        twelvechairs 15y ago
        English dropped grammatical gender some centuries ago. Despite being 'less specific' in some ways, I'm not sure too many would argue that this was a step backward.
    - _delirium 15y ago
      If anything, I think this one is going the other way: traditionally there wasn't a distinction, but one seems to be emerging more recently.
vilhelm_s 15y ago
My understanding is that "further" and "farther" can be used interchangeably when talking about distances (so "further" can be used wherever "farther" can, but not the other way around). This is for example what the usage note at http://www.merriam-webster.com/dictionary/farther http://www.merriam-webster.com/dictionary/farther says, although they state that the usage is becoming more polarized.

janzer 15y ago

My first thought on reading is this is essentially (at least in spirit) mipmapping[1] applied to his 2D (2.5D?) engine. 1. http://en.wikipedia.org/wiki/Mipmap http://en.wikipedia.org/wiki/Mipmap

daenz 15y ago

Downsampling images before a blur seems to be a pretty standard technique to get more perceived bang (blur) for your buck. If you don't downsample the image too far, the blur adequately covers any artifacts the downsampling (and re-scaling) would have. The result is, an N radius blur can be stretched a lot farther, because the downsampling (and re-scaling) itself adds an blur of its own. This performance optimization doesn't really work for variable-width blurs (like depth of field) on 3d scenes though, because some parts of your image need to be crisp, while others blurred. Downsampling the entire image would lose resolution on the crisp parts. 3d depth of field blurs are actually pretty interesting though. They're variable width, which is just another way of saying that each pixel on the final image might be blurrier or less blurry than another pixel. Implementing this kind of variable blurring is a tough task, and typically done by scaling up or scaling down a disk of random sampling coordinates for each pixel. When the disk of coordinates is large, the sampling coordinates sample further from the pixel its centered on, so the resulting pixel has a bigger blur. When the sampling disk is small, the surrounding coordinates are closer to the center pixel, creating a smaller blur. The size of this sampling disk is controlled by the depth of the pixel from the near and far focus planes of the virtual camera. I've glossed over a lot (like the artifacts that can result from 3d DoF), but Nvidia's GPU gems has a great article on the subject http://http.developer.nvidia.com/GPUGems3/gpugems3_ch28.html http://http.developer.nvidia.com/GPUGems3/gpugems3_ch28.html

Retric 15y ago
In 3D games with significant view distance, they often use low resolution copy's for displaying distant objects. These low resolution copy's are progressively replaced with ever more complex versions as you approach. I suspect you could mix in some blur to get a smoother transition and enable even lower resolution copy's while avoiding the 'pop' that occurs when you suddenly get the high rez version of an object.
mrhyperpenguin 15y ago
> This performance optimization doesn't really work for variable-width blurs... An alternative would be to use Summed-area tables [1] where each texel contains the sum of all texels that are above and to the left of the current texel. This allows variable-width blurs to be computed in constant time, using only four texture samples (!). And the concept of a variable-width blur is an approximation to a related concept in photography/optics called the "circle of confusion." [2] The circle of confusion, combined with bokeh sprites, are usually what AAA games are doing for depth of field [3]. See [4] for more details. [1] http://http.developer.nvidia.com/GPUGems3/gpugems3_ch08.html http://http.developer.nvidia.com/GPUGems3/gpugems3_ch08.html [2] http://en.wikipedia.org/wiki/Circle_of_confusion http://en.wikipedia.org/wiki/Circle_of_confusion [3] http://udn.epicgames.com/Three/BokehDepthOfField.html http://udn.epicgames.com/Three/BokehDepthOfField.html [4] http://mynameismjp.wordpress.com/2011/02/28/bokeh/ http://mynameismjp.wordpress.com/2011/02/28/bokeh/