preview discrepancy

[Kevin F]

Anyone had this happen and what the problem is?
As you can see the lighting in the preview is nothing like the rendered version.

[PG]

Oddly, even though it says finished at the top of the preview, it only looks like it's on about 40%... I know there is some difference between the preview and the render because of not being able to do GI in the same way or something but I wouldn't think it would be this much difference. As I said the scene looks very low poly still. The quadrilaterals that make up the scene are usually quite small by the time it's finished.

[JimB]

I've had more discrepancy than that. I only use the Preview window for composition, and use a very small render to check instead.

[jo]

Hi Kevin,

Although much of the time the preview will be pretty close and it does use essentially the same process as full renders, it's not really intended to be perfect. There are a few shortcuts taken to ensure reasonable speed and in some images these can have more effect than others. To really get the effects of lighting especially it's a good idea to do a small render.

Regards,

Jo

[Kevin F]

Thanks Jo, most other times the preview renders fairly close to the final version, but with this one the difference was bigger than I'd seen before. The annoying thing was having seen the preview I'd left the render on overnight and woke up next morning to the darkness!

[rcallicotte]

I've seen this quite a few times and overlooked it as an inadequacy in the program.  It would be nice if it worked correctly, though.

[Matt]

To render 'correctly' all the time, it would need to take a lot longer to render the preview. That's certainly true for GI, but in this case the I think the problem is shadow-casting geometry. The low-res preview does take more shortcuts with shadow geometry than it probably should. I can look into improving that in future versions.

Matt