motion blur (and animation)

[Henrik]

Today, I started playing around with the motion blur feature in LuxRender and animations in Blender. I'm trying to recreate the effect that appears if you take a photo of a moving light source with a long exposure. It works fine as long as the movement happens in one frame. I want my light source to move along a path object, but I have no idea if it is possible to capture the whole movement, which is usually longer than one frame. If I make the animation only one frame long, the light source moves along a straight line between the beginning and the end of the path and not along the path itself. It is possible to do that? How?

Henrik

[thomas]

I think one thing you could do is render the 'animation' as separate frames with motion blur to exr files and add them together manually. In photoshop you could use the Lighten or Screen blend mode to do that, I don't know which one exactly as the names are rather cryptic. If it are a lot of frames it becomes a bit tedious, there might be other tools I'm not aware of, but it is something that might work, if you have ph installed of course.

But is it possible to apply motion blur to light sources? Because last time I've tried it is was not...

[Henrik]

Well, I searched the forum and read that it was impossible, but I tried it and it worked (as you can see). What you see in the picture is an icosphere with some faces which have a light material. I separated the different materials to independent objects because of a bug (?) in LuxRender that appears if you use light emitting materials and other materials on the same object, which in some cases makes the whole object emit light. I had to set the gain of these faces to 100 to make them more visible (the background is light by a few separate light sources). I use version 0.6 RC6, maybe it has something to with that.

[zsouthboy]

This isn't luxrender specific, if you have all the activity happen during 1 frame, you'll only see the end result (since it's calculated once per frame). Render in blender internal (or any other package) and you should get the same thing.

[Lord Crc]

While it may appear to work, it's not an area we've looked hard at yet, and as such it may not be correct at all. Just something to keep in mind

We'll look more at this after 0.6 is out.

[Henrik]

I think one thing you could do is render the 'animation' as separate frames with motion blur to exr files and add them together manually. In photoshop you could use the Lighten or Screen blend mode to do that, I don't know which one exactly as the names are rather cryptic. If it are a lot of frames it becomes a bit tedious, there might be other tools I'm not aware of, but it is something that might work, if you have ph installed of course.

The idea is good, but in order to get a smooth animation, I probably need 50 or more frames, because the movement in every single frame is straight and not curved when I use a path object. Putting them together is a great job for a computer. I don't know how LuxMerger works, but wouldn't it be possible to make LuxRender do that on its own? It would be cool in a sense of "it's possible with a real camera, and LuxRender works like a real camera, so it's possible with LuxRender", but I don't think a lot of people would use this feature.

[Lord Crc]

Luxmerge requires the following things to be equal between the flm's:

• resolution (width / height)
• number of lightgroups
• integrator (mainly bidir or non-bidir)
• sampler (mlt/erpt vs random/ld)*

*fairly sure about this one.

Other than that it's quite "dumb", and will happily merge whatever.

[thomas]

Yes ofcourse, luxmerger would be the way to go. Let us know how it turns out, I have been wanting do a night render in a city with long exposure times for a long time.

[thomas]

I'm sorry, I was too curious of how it would turn out so I gave it a go. For starters Lux complained there weren't any light sources to render, so I added a little sunsky to the mix. I set it to render 100 frames at 32 spp, there were quite some disturbing frames within the output but I hoped they would even out in the end when blended all together, also I doubt that the lights actually lit any of the scene apart from direct lightning, but maybe this has to do with limited amount of samples and I rendered with path.

Well, the result is really not that nice. But the workflow is amazing (apart from an already reported minor bug in LuxBlend), just render them all and merge them in luxmerger. Even light groups where still functional so I was able to balance sunsky and car light contributions in the final result. I was afraid there were going to be brightness differences in subsequent frames, but I noticed none of those. I can imagine in a later stadium this could even become a little button in luxblend, to render a merged animation.

100 frames with motion blur merged with luxmerger, than tweaked lightmaps, than tonemapped.

[tomb]

Hi,

Possibly I'm misunderstanding something here Have I understood it right, that you're rendering a 100 frame animation and then merge the individual frames' flm files
to a single still using the luxmerger tool? I may be wrong, but I think the luxmerger tool was primarly made for merging the flm files for a single frame rendered over
many/several luxrender instances, not as a tool for compositing animation frames to simulate motion blur Because if you're using it like this, I think it's no wonder
you get a odd results... Motion blur in lux works the same way as the shutter speed on a DSLR camera, i.e. it captures the motion within a single frame - an animation with
motion blur is therefore just a sequence of shutter-speed rendered stills.

T