Hdri differences in rendertimes

[francomanko]

So i'm posting this in the max forum as more people are likely to have used them, but im rendering in maya (shouldnt make a difference)...

Anyway...im using a peter guthrie hdri and the render comes out as 13 mins...i use a cg source one and its 6mins. These are the two images...

I was just wondering if other people have experienced similar things? I know its not that fair to compare hdri, but theres quite a difference in rendertimes.

Also when i open PG hdri in photoshop, the image is fully exposed with the 32 bit slider only half way (the default), with the CGsource one, it behaves seemingly correctly, with exposure levels either side of the half way point. Could this be something to do with it? (ive attached a screenshot showing sliders etc)

Any help/info much appreciated.

Cheers

[Muhammed_Hamed]

Some HDRIs will render slower than others, you will see this specially with interior HDRIs.. Some of them can be 3x slower
This is normal I think, your renders are identical so maybe use the HDRI that render faster? but maybe there will be a difference in shadows? place a sphere or a cube on floor and rerender
I'm not sure why the PG HDRI is fully exposed, maybe someone here knows why
Are both HDRIs the same resolution? This can affect render time as well.

[Grigio18]

the difference in display between the two hdri depends on the fact that the cg source ones have been normalized to contain all the dynamic range that was captured during shooting.
To obtain a realistic exposure level in photographic terms you will have to increase the intensity of the dome.

Those of PG are generally linear, but this means, as far as I know, a loss of information ...

here an explanatory reading imho: http://www.reedbeta.com/blog/artist-...posure-values/

[francomanko]

yeah i dont really want to compare hdri for render times, it was just that i was getting such a difference in rendertimes, also my final shot was 6hrs on a 3 machine i7 render farm..which is pretty crazy. Thanks for the info though..ill read up on that link too.

[kosso_olli]

You attached the same image twice for the render, the file names are identical.
I suppose one of the HDRIs is having a the sun exposed correctly, which would explain the higher render time.

[francomanko]

oops sorry, updated. Yeah i just wanted to check i was doing something wrong tbh.

[kosso_olli]

Ah, I see. One of the HDRi is having a much brighter sun. I suppose it is the one you just updated, and I think this is also the one that renders longer. That would be totally normal, given the high intensity of the sun, the area shadow sampling etc.

[francomanko]

yeah it is, good to know, thanks fella, much appreciated.