Hello, I’m quite new to rendering in unreal. I’ve been trying to output a motion vector pass to apply motion blur in post-production, but I can’t seem to find how.
When I add the additional render pass for the motion vector in the MRQ, the pass contains no information (all still yellow-ish) while it should because there is a character moving. The only way to have info be visible out of this render pass is to have an object moving at incredible speed back and forth, abnd even then, the vector pass seems to not contain lots of info. How dfo I fix this?
After thoroughly looking into this, I think I may have some information to help you out.
The fact that you stated it’s noticeable when you have fast-moving object hinted to me that your velocity pass is indeed working, you just can’t see it very well. Indeed, when I replicated the setup on my end, at first it looked like I had an empty frame, but when I went into Photoshop and played with the levels, you can see that, while slight, there is a difference in information.
If you perform this same test and are still not getting any results, I’ve seen suggestions that disabling Nanite or your Anti-Aliasing might help.
If you are getting some amount of information, that’s great! This might be all you need- I would suggest trying to use these frames in your compositing package. Vector information in Unreal is usually very slight like this, so it’s not abnormal to be seeing results like this.
According to the Unreal Documentation, compositing software like Nuke will require a conversion, since Unreal’s motion vectors are normalized in a 0-1 range, while Nuke requires its motion vectors in a -0.5-0.5 range and relative to the screen position. If you follow the link, you can see a little breakdown of the conversion logic.
If you are still not getting any results, let me know and send some screenshots of your render setup, and we’ll see where we can go from there. If you would like to continue troubleshooting on your own, or if you would like to better understand what is happening behind the scenes, I would suggest playing around with (but not saving) the MRQ Motion Vector postprocess material. To preview it in-engine you can add the material to a postprocess volume.
I will be running some more tests, but when I do put a frame into photoshop, it does appear to be some faint info in the image. Thank you. I’ll let you now if it still doesn’t work.
