Eevee's ground truth motion blur (steps) no longer working #79646

New Issue

msalv · 2020-08-08T17:18:51+02:00

msalv commented

2020-08-08 17:18:51 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.67

Blender Version
Broken: version: 2.90.0 Beta, branch: master, commit date: 2020-08-07 15:11, hash: a93be410c9
Worked: at least 2020-06-26 17:24, hash: b7b57e7155 , probably later

Short description of error

Using motion blur by increasing the Steps value is not working. Also, the postprocessed motion blur (the one that works with the Max blur value) only behaves correctly with 1 Steps of ground truth motion blur, with more, it becomes increasingly smaller.

b7b57e7155:

a93be410c9:

Exact steps for others to reproduce the error
Download this file and render with both versions to compare: mbtest.blend

Suggestion

In the version that works, I noticed that a forced motion blur step is essentially the same as a render sample, taking care of antialiasing, shadows and such. So I often trade Render samples for MB steps because 64samples * 1step = 1sample * 64steps. You get a fast rendertime, but with accurate motion blur, which is really good.

I suggest to 1: Make this automatic in the UI, so in essence the 1 to 1 trade happens under the hood by itself when you turn on forced motion blur. If the render has 64 samples, the motion blur will have 64 samples (which is actually 1 static sample * 64 motion steps so it will be fast) And 2: Make the postprocessed motion blur, which only affects geometry, optional with a tick box, or get rid of it altogether. It seems to me like this was added because Forced motion blur seemed slow to render multiple steps, but it's only slow because the interface by default doesn't make it intuitive. A tick box and subpanel to separate it would make it more clear that these are two different motion blur techniques, right now its confusing to the user how these two behave together (eg Background Separation and Max Blur belong to postprocessed motion blur)

The forced ground truth motion blur is important for my workflow, it would be a shame if we never get it working back again, the postprocessed one isn't enough. I hope this is a bug and not a sudden change of heart of not having it

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.67 **Blender Version** Broken: version: 2.90.0 Beta, branch: master, commit date: 2020-08-07 15:11, hash: `a93be410c9` Worked: at least 2020-06-26 17:24, hash: `b7b57e7155` , probably later **Short description of error** Using motion blur by increasing the Steps value is not working. Also, the postprocessed motion blur (the one that works with the Max blur value) only behaves correctly with 1 Steps of ground truth motion blur, with more, it becomes increasingly smaller. `b7b57e7155`:![worked.png](https://archive.blender.org/developer/F8759318/worked.png) `a93be410c9`:![notworking.png](https://archive.blender.org/developer/F8759319/notworking.png) **Exact steps for others to reproduce the error** Download this file and render with both versions to compare: [mbtest.blend](https://archive.blender.org/developer/F8759322/mbtest.blend) **Suggestion** In the version that works, I noticed that a forced motion blur step is essentially the same as a render sample, taking care of antialiasing, shadows and such. So I often trade Render samples for MB steps because 64samples * 1step = 1sample * 64steps. You get a fast rendertime, but with accurate motion blur, which is really good. I suggest to 1: Make this automatic in the UI, so in essence the 1 to 1 trade happens under the hood by itself when you turn on forced motion blur. If the render has 64 samples, the motion blur will have 64 samples (which is actually 1 static sample * 64 motion steps so it will be fast) And 2: Make the postprocessed motion blur, which only affects geometry, optional with a tick box, or get rid of it altogether. It seems to me like this was added because Forced motion blur seemed slow to render multiple steps, but it's only slow because the interface by default doesn't make it intuitive. A tick box and subpanel to separate it would make it more clear that these are two different motion blur techniques, right now its confusing to the user how these two behave together (eg Background Separation and Max Blur belong to postprocessed motion blur) The forced ground truth motion blur is important for my workflow, it would be a shame if we never get it working back again, the postprocessed one isn't enough. I hope this is a bug and not a sudden change of heart of not having it

msalv commented

2020-08-08 17:18:51 +02:00

Added subscriber: @moisessalvador

Cycles commented

2020-08-08 22:43:13 +02:00

Added subscriber: @Cycles

Cycles commented

2020-08-08 22:43:13 +02:00

About 1: It should be an option. If a user is only using one sample and there are post process blur artifacts then they might be confused as to why there are artifacts, while controlling the steps from the motion blur panel makes it intuitive that it should change the quality of the motion blur. Global samples shouldn't change the quality of a given effect, it should simply average randomized samples of the render. Effects like anti aliasing don't "care" what the global samples are. They simply randomize each sample and it will eventually converge. On the other hand, the motion blur would have to take the global samples into account for each sample so there would be accurate post process blur. Having it use global samples would be more practical but much less intuitive.

What I think there should be is a check box next to steps saying "Use Global Samples" which would set the steps to the global sample value. This would both make it the user's choice how Blender decides the steps and clear it up to the user that it is actually using global samples for the motion blur steps when it is enabled. It gives the user control while still making the process semi-automatic.

About 2: I definitely agree that we should keep step based motion blur. However, the post process motion blur is meant to be used to blend between multiple steps. Although you can use post process blur by itself, it intertwines with time step blur so the two techniques should not necessarily be separated. I think the current system makes sense since in most cases users would want to use both of them together. Of course if you wanted to just use step based motion blur you could set max blur to zero (assuming this is actually a bug and it gets fixed) or set steps to one for only post process blur.

About 1: It should be an option. If a user is only using one sample and there are post process blur artifacts then they might be confused as to why there are artifacts, while controlling the steps from the motion blur panel makes it intuitive that it should change the quality of the motion blur. Global samples shouldn't change the quality of a given effect, it should simply average randomized samples of the render. Effects like anti aliasing don't "care" what the global samples are. They simply randomize each sample and it will eventually converge. On the other hand, the motion blur would have to take the global samples into account for each sample so there would be accurate post process blur. Having it use global samples would be more practical but much less intuitive. What I think there should be is a check box next to steps saying "Use Global Samples" which would set the steps to the global sample value. This would both make it the user's choice how Blender decides the steps and clear it up to the user that it is actually using global samples for the motion blur steps when it is enabled. It gives the user control while still making the process semi-automatic. About 2: I definitely agree that we should keep step based motion blur. However, the post process motion blur is meant to be used to blend between multiple steps. Although you can use post process blur by itself, it intertwines with time step blur so the two techniques should not necessarily be separated. I think the current system makes sense since in most cases users would want to use both of them together. Of course if you wanted to just use step based motion blur you could set max blur to zero (assuming this is actually a bug and it gets fixed) or set steps to one for only post process blur.

msalv commented

2020-08-08 23:09:39 +02:00

I agree with the option. When I thought about it, and saw that using mb steps as the AA method gave the same results on the static parts of the image, I too was worried about the moving parts. Would they be too artifacty? But on my results, given the individual contribution of each sample is so faint, the alias of an individual moving step is not noticeable, but I guess it will be more noticeable with very small, very bright parts, which is the only case I can think of, that's why I'd prefer my suggestion as default. This also opens the door to a larger argument about customizing samples for other things that now are tied together to the one and only render samples, like soft shadows or alpha hashed materials.

Anyway, these are just random suggestions and the bug itself is what has priority. I hope I didn't derail the report with my suggestion and that the bug is noticed by the devs, please 😭

I agree with the option. When I thought about it, and saw that using mb steps as the AA method gave the same results on the static parts of the image, I too was worried about the moving parts. Would they be too artifacty? But on my results, given the individual contribution of each sample is so faint, the alias of an individual moving step is not noticeable, but I guess it will be more noticeable with very small, very bright parts, which is the only case I can think of, that's why I'd prefer my suggestion as default. This also opens the door to a larger argument about customizing samples for other things that now are tied together to the one and only render samples, like soft shadows or alpha hashed materials. Anyway, these are just random suggestions and the bug itself is what has priority. I hope I didn't derail the report with my suggestion and that the bug is noticed by the devs, please 😭

Cycles commented

2020-08-09 00:05:29 +02:00

Yeah, not having step based motion blur would kind of defeat the point of the new improved motion blur in 2.90. Let's hope that we get step blur back! 😁

RedMser commented

2020-08-10 01:47:58 +02:00

Added subscriber: @RedMser

Philipp Oeser commented

2020-08-10 10:26:53 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-08-10 10:26:53 +02:00

Isnt this the same as {#79672}?

Philipp Oeser commented

2020-08-10 10:27:23 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2020-08-10 10:27:23 +02:00

Added subscriber: @fclem

Philipp Oeser commented

2020-08-10 10:27:23 +02:00

CC @fclem

msalv commented

2020-08-10 10:32:13 +02:00

If post processed motion blur is used to blur between ground truth motion blur steps, then both problems are caused by the same issue, GTMB not working, so yeah

Clément Foucault commented

2020-08-12 18:20:20 +02:00

Closed as duplicate of #79672

Clément Foucault closed this issue

2020-08-12 18:20:20 +02:00

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Eevee's ground truth motion blur (steps) no longer working #79646