Reduce dynamic range of a hdri (vrayhdri map)

[Crayox13]

I only recently started to use vrayhdri and dome lights (I used vray sun/sky auto system before). I have great hdris but just want the sun to be much less bright for an interior scene. So can I reduce the dynamic range of it?
thx

[urbanite]

Increase the hdri gamma.

[LudvikKoutny]

I would not mess with gamma. It will change your entire HDRI map... in case of increasing gamma, HDRI will become washed out. Instead, do this:
https://www.youtube.com/watch?v=5H320ZvYHag

This also works the other way, in case you want to boost intensity of sun on some maps. With some more tinkering, you can even make HDRIs out of regular JPEG maps this way.

[Crayox13]

Oh thx Recon, did not think of that. Maybe vrayhdri could also have like a dynamic compression number? Or is that unnecessary? Something similar to that thing you have when you load it with MAXs bitmap.

[LudvikKoutny]

I just checked and VrayHDRI has the exact same curve tool in the output roll-out, so you should be able to do the exact same thing.

[Vizioen]

I would not mess with gamma. It will change your entire HDRI map... in case of increasing gamma, HDRI will become washed out. Instead, do this:
https://www.youtube.com/watch?v=5H320ZvYHag

This also works the other way, in case you want to boost intensity of sun on some maps. With some more tinkering, you can even make HDRIs out of regular JPEG maps this way.

That's actually a quite interesting approuch, never thought of doing it like that. You're the first one I come across that claims to do it this way. Everybody says, fiddle with the gamma/multiplier.

[^Lele^]

There are very good reasons to NOT use it.
That's only going to work when the data you want to preserve is in the 0-1 range, and anything above it is going to be multiplied by the key sitting at 1.0.
I'm not sure how rangy your HDRIs are on average, but that output ought to be left alone unless one's working with 8bit, clamped imagery.

A selective multiplication of image areas ABOVE 1.0 can only be had in Post (whereby you isolate the range you want to work on, ideally with a soft clip so no banding will happen) or, as others said, by playing with gamma and multiplier in the VRayHDRI map itself.
Gamma will skew the balance between brights and darks (in other words, compress or expand the dynamic range), and the global multiplier will rescale the resulting image to the ranges you want, INCLUDING anything that is above 1.0.

Ofc, feel free to do as you please: if it floats your boat it floats your boat.

[Vizioen]

There are very good reasons to NOT use it.
That's only going to work when the data you want to preserve is in the 0-1 range, and anything above it is going to be multiplied by the key sitting at 1.0.
I'm not sure how rangy your HDRIs are on average, but that output ought to be left alone unless one's working with 8bit, clamped imagery.

A selective multiplication of image areas ABOVE 1.0 can only be had in Post (whereby you isolate the range you want to work on, ideally with a soft clip so no banding will happen) or, as others said, by playing with gamma and multiplier in the VRayHDRI map itself.
Gamma will skew the balance between brights and darks (in other words, compress or expand the dynamic range), and the global multiplier will rescale the resulting image to the ranges you want, INCLUDING anything that is above 1.0.

Ofc, feel free to do as you please: if it floats your boat it floats your boat.

Thanks for the explanation Lele, much obliged. So if I understand correctly: don't use the output map with 32 bit images? I thought the range of an HDRI was scaled between the 0 and 1 accordingly? I've seen people use an output map to change the color of an HDRI though, so that was an incorrect way of doing it?

[vlado]

To limit the values in the HDRI map, you generally just need to clamp the HDRI values to some number; you can use a VRayCompTex texture with the HDRI in one slot, a VRayColor map in the other, and "Min" operation. Adjusting the RGB multiplier in the VRayColor map will give you different clamp values.

Best regards,
Vlado

[^Lele^]

Ahah, clever way, Vlado.

[kosso_olli]

The old Color Correct plugin had a clamp parameter that did what you are after. Sadly it is a very old piece of code and no longer supported for 2017.

[Crayox13]

Thanks for all the suggestions guys. Will of course first try vlados...because, you know...he's vlado

[GRUENDER_AV]

...starting point for the rgb-multiplicator is high! (2000-10000 for peter-guthrie-hdris)

[Vizioen]

...starting point for the rgb-multiplicator is high! (2000-10000 for peter-guthrie-hdris)

I've tested one of his last ones with new sun and that one was around 300.

[^Lele^]

Thanks for all the suggestions guys. Will of course first try vlados...because, you know...he's vlado

That is as good an heuristic as you're ever likely to follow.
I know from personal experience... ^^