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Lucas Milner avatar image
Lucas Milner asked ·

Render Bucket Impact (MAXtoA )

I'm currently rendering an image with render bucket size at 16x16, online documentation suggests that it's faster to stick to the default 64x64, I'm curious how much of a difference this makes? Can you hit me with any general numbers for this mistake that I've made?
Documentation: "The default render bucket size is 64x64 pixels, which is a good compromise; bigger buckets use more memory, while smaller buckets may perform redundant computations."

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Zap Andersson avatar image
Zap Andersson answered ·

In principle you can compute this.

Here's the worse case scenario, assuming the renderer cannot re-use ANY inter-bucket pixels:

Imagine you are calculating a border as wide as HALF the filter width "extra" on each bucket. So if your filter width is 4, each bucket is calculating 2 rows of pixels redundantly outside itself.

bw = bucket width
hfw = half of the filter width

So for a bucket of bw, the "useful" pixels is bw*bw and the number of extra "wasted" pixels are 4*(bw*hfw + hfw*hfw)

So, for 16 pixel bucket and 4 pixels filter width, that's 4*(16*2+2*2)=144 "wasted" pixels and 16x16=256 useful ones, i.e. 56% useless computation!

For a 64 pixel bucket, it's 4 * (64*2 + 2*2) = 520 "wasted" pixels and 64x64=4096 useful ones, which is 12% "waste".

You pick :)

Of course, default filter with is 2.0, which makes the waste about half of the above (28% vs 6%), but still...

/Z

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Nicola Jannuzzo avatar image
Nicola Jannuzzo answered ·

With more (smaller) buckets you are wasting some computation time, because, based on the filter width, extra samples must be sent outside of the bucket's frame to be filtered.

A way to correctly banchmark this for you is using kick, so your total rendering time is not affected by translation. Export a .ass file, and in a prompt go to the MAXtoA installation dir.

From there run

kick <full path to the ass file> -v 6 -dp -bs 6

v is the verbose level, dp disable progressive rendering, bs lets you set the buckets squared size.

run kick --help for the full list of options.

Try different bs values, and compare the render logs. In case, let us know about your findings.

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Thanks a lot for your reply Nicola, I've been enjoying learning more Arnold over the year.
I'm interested in running renders via kick and the TX workflow.
Would you say that at 'render time' it is worth converting the scene to an .ass and using tx texture?
I have a bad habit of turning my quality settings up a bit too much and rendering a 4K image for more than 10 hours.

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