Gamma 2.2 vs sRGB image errors

[dlparisi]

I'm getting some strange banding in images (around the edge of the light falloff) while using the 2.2 gamma setting in the color mapping rollout. See below...

Rendered with gamma 2.2 (saved directly as jpg):

A blow up of the banding:


Rendered with gamma 1 (viewed with sRGB switch 'on' and saved as .exr and converted to jpg)

A blow up of the same area:


If I understand sRGB correctly, the gamma near black is closer to 1 rather than 2.2. Is this the reason for this strange effect? Is there any way to save the sRGB viewed image directly from the frame buffer? The saved file looks slightly different then the render buffer when a gamma of 2.2 is specified (that's why I saved to exr and then converted to jpg).

For the time being I can use the exr method for this image and use my regular 2.2 gamma on my usual stuff since this is the first time I've noticed it.

[tricky]

I too have noticed differences between the sRGB preview of the VFB and the saved EXR format file in Photoshop.

[dlparisi]

Actually the sRGB preview button in the VFB seems to match OK to the saved exr viewed in photoshop. I'm noticing the banding issues when I set the gamma in colormapping to 2.2 and leave the sRGB preview button off.

[pengo]

excuse me dlparisi maybe I misunderstood what u do as method, but in me
if u use to save image from vray vfb and checked srgb on and save to exr u save the imge with double gamma applied
If I misunderstood tell me how u do please
thanks to make clear the problem
have nice day

[throb]

part of the reason is probably due to how much 3dsmax sucks

additionally 2.2 gamma is NOT sRGB as you are all seeing. it's a close approximation.

my advice is to save out vrimg files from vray renders and then convert them to exr's via the vrimg2exr tool.
this is a very tried and true method we use every hour of every day at work. it's very effective and very accurate. vrimg files are pure 32 bit floating point color so there will be zero banding like what you were experiencing with the original jpg.

don't ever use the 3dsmax frame buffer either. it's crap.
also don't bother with the 3dsmax image savers. do it all thru vrimg. there is development going on to save out exr's directly from vray thru its framebuffer so don't worry, that will be easier in the long run too.

rob

[dlparisi]

pengo: I haven't noticed any double correction. The problem I'm having isn't really about the saving of the files anyways-it looks like that in the vray frame buffer as well.

throb: Yeah, I had noticed that sRGB is not the same as 2.2 gamma, especially near black, and that's where I'm noticing the problems. Saving out to vrimg is a great idea but it's not really convenient for test renders and progress images, especially with the extra step of converting it to exr so we can open it in photoshop. The images above appear the same way in the vray frame buffer, so it's not related to how it's saving out the image so it's probably the sRGB thing.

Does anyone (i.e Vlado) know if the sRGB button applies a true srgb curve to the image or is it simply bumping up the gamma to 2.2? Is it possible to have a sRGB button in the color mapping rollout?

[vlado]

The V-Ray VFB applies correct sRGB transformation near the black colors. The gamma color mapping did not do this originally, which lead to this kind of weird colors near black. This is already corrected for future builds, where dark colors are gamma-corrected in a more reliable way.

Best regards,
Vlado

[dlparisi]

The V-Ray VFB applies correct sRGB transformation near the black colors. The gamma color mapping did not do this originally, which lead to this kind of weird colors near black. This is already corrected for future builds, where dark colors are gamma-corrected in a more reliable way.

Thanks for the confirmation. Looking forward to the future builds (as always but pretty damn happy with current one)!

David

[pengo]

u are right dlparisi because srgb is not saved with the image was my misunderstood