ToneMappingEffect affects the background color

[MajorMeerkatThe3rd]

Currently the ToneMappingEffect affects the background color, this can be reproduced on the demo page.

It would be very helpful to have a setting to ignore the background, like for other passes.

[vanruesc]

Hi,

I agree that it would be a useful feature to have, but there are currently no plans to add support for masking to ToneMappingEffect. The reason being transparent objects.

Implementing masking based on min/max depth wouldn't be too difficult. However, transparent objects don't write depth so all transparent fragments rendered on top of the background would no longer be tone mapped. Depth-based masking also causes aliasing artifacts around object edges and it requires additional texture sampling which isn't free.

I haven't tried this, but it might be possible to modify three's skybox shader to output untonemapped/inverse-tonemapped colors (http://www.codersnotes.com/notes/untonemapping/). After applying tone mapping, the final output should then look closer to the original colors.

[MajorMeerkatThe3rd]

Hello @vanruesc,

thank you for this very insightful answer! This makes the complexity of the issue much more clear to me.
Once I find some time, I'll try the suggested approach and will report back!

Thank you!

[vanruesc]

Closing this since there are no actionable tasks. Feel free to reopen if there are any techniques/approaches that could be explored to make selective tone mapping work.

[MajorMeerkatThe3rd]

@vanruesc I found out that it is actually an easy change that can be done to ignore the background. Simply request the depth for the tone mapping effect (EffectAttribute.DEPTH) and in the mainImage function, add this to the end:

if(depth >= 1.0) {
    outputColor = inputColor;
}

It's basically a passthrough for the background. Seems to work very well in my tests.

This could be made an option of course.

[vanruesc]

It's basically a passthrough for the background.

Yes, that's basically what I described here:

Implementing masking based on min/max depth wouldn't be too difficult. However, transparent objects don't write depth so all transparent fragments rendered on top of the background would no longer be tone mapped.

It's not a general solution to this problem, so I don't think it should be added as an option.