Lighting issues with large render

I've been trying to do a larger render size, and have encountered an issue once I go about 5000 x 5000 pixels or so (ultimately I was hoping for a 14400 x 14400 render, to print out at 300 dpi). Without making any changes to the render setup beyond the target size, the resulting image looks blown out - I've attached a comparison image, with 100 passes at packet mode at 4000 pixels square on the left - and 10000 pixels square on the right. I let the render complete, hoping that the issue was just in the preview window, but that is what the resulting file looks like as well.

I've since tried going up in 1000 pixel increments, which is how I've noticed the 5000 pixel threshold. Within the first pass, the lighting blows out - often halfway through the pass the lighting looks correct, but will shift by the end of the pass.

Am I overlooking something obvious here? Apologies if so, am new to this - any help would be appreciated.

Attachments:

render_comparison.jpg, 183 KB

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Permalink Reply by Rich Hart on November 5, 2018 at 5:38pm

I can duplicate this. I don't think anyone has noticed this before.

I'll see if I can figure out what might be going on here.

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Permalink Reply by Rich Hart on November 6, 2018 at 2:57pm

I haven't yet figured out what is causing this, but there is a way to prevent it from happening for a model.

You can set the Initial Illuminance value before you start the rendering and the same value will be used for any resolution that you render to.

To do that:

1. First render at a small resolution to get the value that you want to use. You can see that value by looking at the rendering statistics and get the "WorldAvgLum" value, under the Lighting section:

2. Then, before rendering at the large rendering size, on the Light Balancer dialog, set the value for the Initial Illuminance value to the number read from the rendering statistics, and check the box to always use that value, as below: