OTOY Forums

Hey folks,

I just had an idea of how to get rid of hot pixels, and it works extremely well.
You do the following: Render your image (or your animation) twice. Then use Photoshop (or a video compositing app) to put one image over the other and blend them with the blend mode "Darken."

Look at this comparison. The first two images are the two renders, the third image is what happens when you blend them with "Darken":


Keep in mind that hot pixels can still remain visible if a hot pixel is in the same position in both images. This happens especially in areas with a very high density of hot pixels. But you could even do a third pass and layer it on top.

Also, both images should render for roughly the same time. In the example I posted above, the top image rendered for only 1/5th the time of the second image, so it's grainier. These grains also darken the underlying image. Ideally, both images should be absolutely identical except for the placement of the hot pixels.

Nice Idea ..

Now thats an interesting approach, though isn't re-rendering something we're trying to avoid with Octane?
Good thing Octane renders fast, I'll have to try this next time I get a lot of hot pixels.

Interesting idea.
I'm just finishing a little simple program for removing fireflies. If it'll do any good I'll make it public.

Ha
Well, here's mine:
(it can smooth image like above if needed)

kivig wrote:Ha
Well, here's mine:
(it can smooth image like above if needed)

Looks good, how does it work ? does it have a batch mode to handle multiple files for animation ?

2.3 will fix the problem anyway so don't waste too much time on this.

It just searches for bright pixels and replaces them with average of surrounding. Simple as that. No smearing, no sharpness loss.
Batch processing is what I'm doing right now.
Yeah I know, it's too simple not to be inside Octane. Though I'd prefer no smart filters by default.

thank you guys,
interesting alternatives solutions pending the 2.3 release.

this is the 2x render technique, it's already done before a long time ago, if i remember correctly, a few years ago.
offcourse it's not fun having to render the image twice, although if you let them render each the same time and mix them 50/50 you will get 2x less noise.

Radiance