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I tried to find information about this, but I was probably looking for the wrong words. I am not from the rendering community, so I might be oblivious of many basic things.

The problem I have is shown in the attachment below. I am using the Maya plug-in. I created a basic scene with a camera and a daylight environment. I assigned a glass material to an object, and launched the rendering using the default settings. Over time, white dots appear all over the glass surface.

The dots are white, but if I play with the parameters of the materials they can get them to what looks like random colors. Changing kernel type does not really solve the issue. With PCM it looks better at start, but eventually white dots appears and make the image non usable.

How is this form of artifact called? How does one deal with these?

Thank you!

These could be Fireflys. Fireflys are white dots that appear when you have too many reflective surfaces or too many white materials (being white, they reflect much more light than non white). Thing about fireflys, they are always 1 pixel. Your image seems very low resolution, unless you lowered it in photoshop. If you raise your resolution, that 1 pixel firefly will be much much smaller on your image. Also, try to increase the caustic blur setting in your kernel. If you are worried about fireflys, the best option is to use the PMC kernel.

Because that is glass, it might also just be reflecting your light source. did you try different lighting options?

kavorka wrote:These could be Fireflys. Fireflys are white dots that appear when you have too many reflective surfaces or too many white materials (being white, they reflect much more light than non white). Thing about fireflys, they are always 1 pixel. Your image seems very low resolution, unless you lowered it in photoshop. If you raise your resolution, that 1 pixel firefly will be much much smaller on your image. Also, try to increase the caustic blur setting in your kernel. If you are worried about fireflys, the best option is to use the PMC kernel.

Because that is glass, it might also just be reflecting your light source. did you try different lighting options?

Thanks for the explanation kavorka! Are firefiles common in rendering? Or are they specific to rendering algorithms? I never encountered them so far, using global illumination / final gather.

For the screenshot, it's low res as I just cropped a portion of the render area, otherwise it'ss 720p. The white dots appear one pixel at the time, so they could exactly be what you are saying.

I quickly tried to remove the daylight system and put a flat gray texture and the white dots no longer appear. But if I add a light they come back. I have to admit I am a bit surprised by how sensitive this issue is.