sub pixel mapping "problem"

[PEgaz]

hi

if there was the answer for that question - please, don;t kill me - I just couldn't find.

I'm rendering flythrough animation and I'm really tired of seeing all the white splotches dancing in reflections (it's an interior - with few (not so bright) IES lights, sun (hidden) and sky; the white splotches even showed with AA QMC 3/14).
Sub-pixel mapping turned on made everything of course to work pritty well - with one problem - sub-pixel mapping means clamping - and I'd love to use 32bit EXRs as my frames for animation to have the possibility to control everything in postproduction.

is there any way to avoid splotches in reflections without clamping output to regular RGB 8bits? and to have benefit of 32bit output later in any composition software?

regards
PEgaz
www.ante.pl

[instinct]

Just as a sidenote. You still get the benefit of 32bit when rendering with subpixelmapping. Technically speaking the bigger advantage of float happens between 0 and 1. There are more values between 0 and 1 then between 1 and infinity with floating point numbers. You do of course loose the dynamic relation between very bright and normal areas. The only way to get around this is sample as hell, or clamp down less to get a compromise (clamp to 5 instead of 1 for example)

Regards,
Thorsten

[vlado]

You can clamp to a value like 5 or 6 to get a bit of high dynamic range.

Best regards,
Vlado

[PEgaz]

thank you for your hints
I thought sub pixel mapping clamps it at 1 - and there's no way to change it.

just to clarify:
1. I do use sub pixel mapping with clamp option turned on too and set to 5 or 6
2. or I turn off sub pixel mapping and use clamping with value higher than 1
?

regards
PEgaz
www.ante.pl

[Guest]

thank you for your hints
I thought sub pixel mapping clamps it at 1 - and there's no way to change it.

just to clarify:
1. I do use sub pixel mapping with clamp option turned on too and set to 5 or 6
2. or I turn off sub pixel mapping and use clamping with value higher than 1
?

I would like to know this as well. It is always stated to turn on sub pixel mapping and clamp output but never use just one or the other. Do they both need to be on to work effectively?

[tashko.zashev]

Basically it depends on the scene/case, sometimes turning on only Subpixel mapping will be able to reduce the brighter spots over the surface.
But sometimes these bright spots are with very high (white) value and the antialiasing is unable to properly approximate between the normal and the over bright areas.
Therefore is better to set a limit (Clamp output) for the maximum value, together with the subpixel option.

[Guest]

Thanks for the info. So you would never just use clamp output on its own at say 5?

[3DMK]

Just as a reminder that you usually get those damn white spots more when you have a very contrasting scene lighting or sometimes from lights behind refracted materials.
Sometimes it's best to prevent such lighting setups so that you never have to use SPM or clamping.

Hope this helps