Wild pixels in IBL sampling

Project:YafaRay
Component:YafaRay Core
Category:feature request
Priority:normal
Assigned:David Bluecame
Status:closed
Description

Some hdri backgrounds produce "wild" pixels which are very difficult to smooth out and increase a lot sampling requirements for backgrounds. This usually happens with background images with very strong highlights I believe. This issue is also reported here. I would be good if we can find a good and phisically correct solution about this.

HDRI is downloaded from here (Port Syros low res) :

http://www.openfootage.net/?tag=free-download

You can also download it from https://drive.google.com/file/d/0B9Xy9o3kawnQMmhxbV9sbTBRQnM/view?usp=sh...

Blender example below. Greetings.

AttachmentSize
wildpixels.jpg66.21 KB
test.zip72.44 KB

Comments

#1

Assigned to:Anonymous» David Bluecame
Status:active» needs review

Hello,

This is caused by the montecarlo sampling of the HDRI lighting. When a very bright part of the HDRI is picked, it causes the sample to be very bright (firefly).

There are several possible solutions/workarounds for this:

* (currently available) select a Clamp value, for example, 4.0. This would limit each sample to have a max.brightness of 4, reducing the fireflies. This can also reduce a bit the realism of the scene, but if chosen carefully it will keep the scene realism while greatly reducing the noise and render times.

* Implementing a SmartIBL system, where we can select a low-res blurred version of the HDRI for lighting and a high-res for reflections.

* Perhaps investigate importance sampling. Not sure if this is already implemented in YafaRay or not, I have to investigate.

 

Please try the clamp workaround for now and let me know if it helps.

#2

Hi David

Thanks for looking into this. As per my notes, importance sampling is implemented in background lighting, as noted here. Thanks for the clamping trick.

My work · Grey18 workflow · Sampling strategy · [url=http://www.yafaray.org/node/816]SPPM

#3

Status:needs review» ready to commit

Hello,

The new "SmartIBL" functionality will be available in the upcoming YafaRay v3.0.0

More details here:

http://www.yafaray.org/node/566#comment-1536

#4

Status:ready to commit» fixed

Fixed in v3.0.0-beta: http://www.yafaray.org/community/forum/viewtopic.php?f=15&t=5173

#5

Status:fixed» ready to commit

Hello,

I think I found the fundamental reason for the wild pixels. This commit should fix most of them:

https://github.com/YafaRay/Core/commit/543e2a447742ad1f6d2b9f9a5197f2ded...

This will be available in the upcoming YafaRay v3.0.1-beta

#6

Status:ready to commit» fixed

IBL sampling fixed in v3.0.1-beta: http://www.yafaray.org/community/forum/viewtopic.php?f=15&t=5173

#7

Status:fixed» by design

Marked as "fixed" for more than 3 weeks without any further user comments. Closing.

#8

Status:by design» closed

Selected mistakenly "by design" while trying to close. Setting it to Closed now.