On 6/17/19 11:08 AM, BayashiPascal wrote:
> Hi there,
> I've realized something I wasn't aware until now and wanted to ask for your
> opinion. 
...
> 
Hi Pascal,
I had a little time this morning before being busy with real life. So, 
thought I'd play with what you posted but in the current v3.8 master 
branch as it's the only place anything might be updated.

I rendered your scene at 400x400 instead of 100x100. To my surprise 
using only the default +a type anti-aliasing I see a pixel or sometimes 
a few which are 1/255 by channel in magnitude different(1). In the 
400x400 render, and just +a, this happens with a single pixel at 231,218 
which isn't even on sub-render boundary. Using still method one but 
with: +am1 +a0.1 +r3 I see again that pixel and an additional 2 in the 
same column above it. All near the edge of the sphere so AA is in play. 
Weird. Guessing maybe some sub pixel offset when rendering sub blocks.

The image attached used the new to v3.8 +am3 mode. In the top row two 
different full renders are compared and they match exactly. In the 
bottom we compare the top left full to an image assembled by chunks. The 
multiplier on the differences is 4x. Looks like +am3 better brings out 
whatever the issue is.

Still, not sure I'll open up an issue. Something like this is going to 
be way down on anyone's to-do list. Opinions?

You could try +am2 in 3.6 as I've not see issues with it in 3.8. 
Probably also faster. The jitter off comments others made stands. I also 
tested with one thread to be sure threads>1 not a problem in v3.8.

Bill P.

(1) - Not thinking about it very much - in 3.6, if not using 
assumed_gamma 1.0, the differences might be a little more dramatic in 
the resultant image though probably still hard to see.

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