Rendering erros

Something curious is happening. Here's an exported image from UF. Looks right.

Here's what I get when rendered (normal anti-aliasing, forced linear drawing).

Noticeable differences, not subtle. Not solved by changing anti-aliasing parameters or precision. And if I render the same thing again, different results!

These are done with all 12 of my CPU's cores (6 real cores). If I allow only 1 core, it's repeatable.This seems right except for a bit of black in the lower left corner.

Here's the upr (I've just updated jlb.ulb, so you'll need to update your formulas to compare.) Do others get similar results? Is this a UF bug or do I have a problem?

Thanks for trying.

test {
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}

Hi Jim. Same thing here. Top is export with no glitches. Middle and lower are renders, both glitchy, but different in the lower left corner.

Thanks, Eric. It's not just me!

No, it's not just you, it's even worse here. I see glitches both on renders and onscreen (and thus the exports too). Re-drawing the screen changes the result onscreen every time. I have yet to see a non-glitch version!

I saw something similar to this some years ago which rather ruined a design I was working on. I think the cause was attributed to the CPU at the time. I never found a solution. :|

My CPU is an AMD Ryzen 9 3950X.

My CPU is Intel core i7 8700K.

Apple M2 below. As before, the export looks fine but the renders are glitchy and different. My previous post was with an I7 8700B. I used the Mac version of UF for both sets.

My exports look like each other but they don't look like Jim's export. The middle right section of Jim's has a staircase between the vertical blue bands which are 2nd and 3rd from the right. My exports have a straight line there instead.

Try going to View/Preferences/Fractal and setting the minimum and maximum cores to 1. (I don't know how many cores are in modern Apple CPUs.)

If I render (using only 1 core) at 2000 by 2000 instead of 1000 by 1000, the extraneous dark bits in the lower left of the image (as seen in image #4 in the original post) are not there, correctly. Odd.

With max threads and min threads both set to 1, my 600x600 renders are still pretty glitchy but are now identical. Here’s one:

At 2000x2000, still glitchy but better:

Here’s a 2019 post where Phillip had a similar issue. After a lot of testing, he found a thread setting and image size which rendered cleanly.
https://www.ultrafractal.com/forum/index.php?u=/topic/633/certain-image-widths-and-thread-counts-cause-center-part-of-image-to-be-rendered-first/post-1887#post-1887

My problem was only during rendering, after waiting, everything came out fine. I doubt that this issue is related since the end results differ. I'll have a look at the params since this is making me curious.

I'll have a look at it to see what's happening here.