<p>I am unsure whether you're talking about realistic image synthesis or realtime rendering, but either way these two are somewhat connected. The biggest issues in real time rendering are really finding good approximations of the algorithms used in realistic image synthesis, and the effective implementation of those, as well as hardware that supports this - think RTX atm. RTX in games however is pretty limited - it is highly biased (you can't even call it a good approximation of the rendering equation for most non-trivial scenes), so we're still at a point where rasterization based graphics dominate. Ray tracing has many advantages however, like its average O(logn) complexity versus rasterization's O(n) (where you can think of n as number of triangles in a scene). Note that this is asymptotic notation, so the main reason why ray tracing is not currently faster than rasterization is that: 1) the current hardware is highly optimized for rasterization, 2) the number of drawn triangles needs to be relatively large to offset the constant (it's unclear whether so many triangles would even be necessary for a realistic representation of shapes). There are however effects and realism which you simply cannot achieve with the "hacks" from rasterization graphics, ray tracing (or more precisely path tracing) is what we're aiming at- when you hit that for complex enough scenes/materials/participating media at interactive rates you've basically achieved photorealism.
Now as far as unsolved problems in realistic image synthesis go, there are many. They range from good sampling distributions (the best samplers that we know of currently for CG are usually Owen scrambled Sobol, and some low-discrepancy sequences with blue noise properties - but those usually do not extend as well to higher dimensions), good approximations of the radiance in a scene (there are some recent papers from Vorba and Muller on the topic, they usually call it path guiding), dealing with participating media and complex brdfs (think subsurface scattering), spectral rendering (while there are several techniques for this, you can prove that each of those is bad in some aspect), the theory in general dates back to "Lambert's antiquated framework", and while there have been attempts to modernize it similar to what's been done to other fields in physics for example, the best attempt at that as far as I am aware is Christian Lessig's thesis and the publications following it (which btw do not manage to solve the issue outlined fully). You can say that most problems in realistic image synthesis are actually unsolved - the problem is simply very hard mathematically.</p>

CC BY-SA 4.0
2019-04-10T14:08:30.050Z
Sorry i was referring to real-time. For example when it comes to algorithms for AO, have the latest achieved the best result or they have a huge research area for improvement. I am just pointing it out as an example it can be anything.
Code Master
CC BY-SA 4.0
2019-04-10T14:50:40.767Z
First you need to define what "the best result" means here. Also SSAO is quite different from actual (raytraced) AO. "The best" in terms of accuracy is simply raytracing AO until convergence. But since performance is a factor you usually only get screen space AO, last time I checked Scalable ambient obscurance was one of the best in terms of perf/accuracy. While working on RTX some researchers developed a hybrid AO algorithm that combines SSAO and raytraced AO to get both acceptable performance and quality. I believe that's currently the cutting edge.
lightxbulb
CC BY-SA 4.0
2019-04-10T13:00:37.867Z
2019-04-10T13:00:37.867Z
lightxbulb
<p>What problems haven't been solved yet when it comes for instance in rendering,deferred rendering, Volumetric lighting, ambient occlusion or in any other interesting area. When i say unsolved problems, i mean topics in computer graphics that haven't been entirely solved and need serious improvement and maybe new techniques.</p>

<raytracing><rendering><deferred-rendering><volumetric><ambient-occlusion>
Unsolved Problems in CQ to this day?
Code Master
# Unsolved Problems in CQ to this day?

(Asked by: username_0 on 2019-04-10)

What problems haven't been solved yet when it comes for instance in rendering,deferred rendering, Volumetric lighting, ambient occlusion or in any other interesting area. When i say unsolved problems, i mean topics in computer graphics that haven't been entirely solved and need serious improvement and maybe new techniques.

**Tags:** raytracing, rendering, deferred-rendering, volumetric, ambient-occlusion

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## 1 answers

### Answer by username_1 on 2019-04-10. Score: -1

I am unsure whether you're talking about realistic image synthesis or realtime rendering, but either way these two are somewhat connected. The biggest issues in real time rendering are really finding good approximations of the algorithms used in realistic image synthesis, and the effective implementation of those, as well as hardware that supports this - think RTX atm. RTX in games however is pretty limited - it is highly biased (you can't even call it a good approximation of the rendering equation for most non-trivial scenes), so we're still at a point where rasterization based graphics dominate. Ray tracing has many advantages however, like its average O(logn) complexity versus rasterization's O(n) (where you can think of n as number of triangles in a scene). Note that this is asymptotic notation, so the main reason why ray tracing is not currently faster than rasterization is that: 1) the current hardware is highly optimized for rasterization, 2) the number of drawn triangles needs to be relatively large to offset the constant (it's unclear whether so many triangles would even be necessary for a realistic representation of shapes). There are however effects and realism which you simply cannot achieve with the "hacks" from rasterization graphics, ray tracing (or more precisely path tracing) is what we're aiming at- when you hit that for complex enough scenes/materials/participating media at interactive rates you've basically achieved photorealism.
Now as far as unsolved problems in realistic image synthesis go, there are many. They range from good sampling distributions (the best samplers that we know of currently for CG are usually Owen scrambled Sobol, and some low-discrepancy sequences with blue noise properties - but those usually do not extend as well to higher dimensions), good approximations of the radiance in a scene (there are some recent papers from Vorba and Muller on the topic, they usually call it path guiding), dealing with participating media and complex brdfs (think subsurface scattering), spectral rendering (while there are several techniques for this, you can prove that each of those is bad in some aspect), the theory in general dates back to "Lambert's antiquated framework", and while there have been attempts to modernize it similar to what's been done to other fields in physics for example, the best attempt at that as far as I am aware is Christian Lessig's thesis and the publications following it (which btw do not manage to solve the issue outlined fully). You can say that most problems in realistic image synthesis are actually unsolved - the problem is simply very hard mathematically.

> **Comments:**
> **username_0**: Sorry i was referring to real-time. For example when it comes to algorithms for AO, have the latest achieved the best result or they have a huge research area for improvement. I am just pointing it out as an example it can be anything.  
> **username_1**: First you need to define what "the best result" means here. Also SSAO is quite different from actual (raytraced) AO. "The best" in terms of accuracy is simply raytracing AO until convergence. But since performance is a factor you usually only get screen space AO, last time I checked Scalable ambient obscurance was one of the best in terms of perf/accuracy. While working on RTX some researchers developed a hybrid AO algorithm that combines SSAO and raytraced AO to get both acceptable performance and quality. I believe that's currently the cutting edge.  

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