Jan 2012
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Jan 2012
Jan 2012
prashanth-v-srinivasan
Jan '12

Hi,

In view of comparing 32 float rendering between Exr, Iff and Tga, please find the attached image file.

3 images on the left row are direct render from 3D without changing any settings, only changed the format and rendered. 3 images on the right row are color corrected "Gamma reduced to 0.6 (default 1)" and "Gain 0.2 (default 1)".

What we notice here is eventhough render setttings are set to 32bit, TGA clips to 8bit, so we can't use TGA format.

Second, EXR and IFF rendered with 32bit float and contains good color depth range. Advantage of 'iff' render over 'exr' is the 'file size' is lesser. Eventhough IFF renders with less file size, it holds all the values which EXR holds. So we can use IFF format instead of EXR format, right?

I also understand that under one EXR file you can contain many Channels and both LEFT and RIGHT images can be combined, which IFF can't. Apart from this is there any other advantages of using EXR format.

Thanks,

fxnurbs
Jan '12

standard tga is only 8bits so will clamp your values. maya iff if I am not mistaken is only 16bits with a possibility to have a 32bit depth layer.. (to be confirmed).
Exr is a true float format. Coming from maya it is big indeed because uncompressed. Since Maya 2012 you can use compression formats. Don't get worry about it, it is still float and full quality but you cut the size of file. Using zip (1scanline) is perfect for nuke.

The iff format is not really supported by default in Nuke, I am pretty sure you will have faster process of exr in nuke than iff because it is optimised for it.
That an other argument for exr.

We render exr 16bit with zip compression in my compny if i am not mistaken. Float renders are not really necessary except for some passes like position depth.... unless you really need those extra info for the comp, but that will make your files bigger.

At the end of the day, you use what is confortable for you, but avoid tiff !!! tiff is not scanline friendly. Nuke need scanline compatible format (except those it has been optimised for). So using 1 tiff can slowdown your whole comp. because nuke cannot crop it, it has to load the full picture then convert it in ram to a scanline format... your renders will be slower as for your previews..

joojaa
Jan '12

There are no right ways just ways that you understand.

Yeah tga is 8 bit fixed point only, iff is either 8 or 16 bit fixed point with 4 channels and a possible 5th 32bit float depth channel, tough very few programs can actually read that z channel since it contains NEGATIVE values (encoded in 1/-z distance; the direction is naturally negative in the fremebuffer. Good luck using photoshop to process negative values for example. And that means most artists will miss the entire concept on second 1).

Exr has a wide range of bit depth choices even such things as half float, which is at par with 16 bit fixed in size but contains potentially more data in the further ranges (larger space and more data in the near 0 area and data in over 1 area).

Anyway even with compression the deal is simple if you use full float you waste 4 bytes per channel, whith half float and 16 bit fixed you use 2 bytes and with 8 bits you use 1. So a full float image is going to be 2 times larger than corresponding 16 bit and again 2 times larger than the 8 bit.

Tiff is the format that everybody hates, because you can kill and entire manmoth of work with bad choice of tiff.

The biggest advantage of formats like tga is that its very easy to find applications that support the format, which brings in all kinds of tools into the picture, Also at the moment ist easier to find support for iff than exr, and its really hard to find very wide support for floating point pictures. Its not generally a showstopper but you'd be surprised what you can do with a farm of 20 machines that just happen to be sitting there and no licensing constraints and 10 lines of script glue. Not to be underestimated by a long shot.

PS: when you od gamma correction the difference between 16 bit and 32bit float is negligible, things change for depth fields and soem vector field operations tough..

prashanth-v-srinivasan
Jan '12
fxnurbs

Hi fxnurbs. You are right, IFF only supports 16Bit.

I will check on compressed EXR file. I find following issues while rendering EXR32Bit.

  • There seems to be a difference between what we see inside Maya (preview render) and what we see on EXR 32bit render out. Brightness seem to blow up.
  • fCheck or XnViewer doesn't read EXR file. So, how will a 3D artist check his renderers quickly.
prashanth-v-srinivasan
Jan '12
joojaa

Hi Joojaa. I appreciate all the points you had put in. It was very usefull to understand deeply.

Meanwhile, I find following issues while rendering EXR32Bit.

  • There seems to be a difference between what we see inside Maya (preview render) and what we see on EXR 32bit render out. Brightness seem to blow up.
  • fCheck or XnViewer doesn't read EXR file. So, how will a 3D artist check his renderers quickly.

Do you have a work around on this?

prashanth-v-srinivasan
Jan '12

Yes, i found work around. With regard to difference between "Maya Preview rendering output" and "Maya EXR batch rendering output", we tried following settings and it worked great.

Under Maya preview render
Display > 32-bit floating point (HDR)
Display > Color management > Image Color Profile > Linear
Display > Color management > Image Color Profile > sRGB (default)

Now whatever we see inside Maya, exactly matches with the EXR batch rendered frame.