32bit images

V-Ray for 3ds Max V-Ray for 3ds Max :: General
1

We have a job at the moment where the exposure is not straightforward: it is a view from inside an apartment looking out through a large bay window. To create a balanced image (not too much blow-out, not too much underexposure), we are going to be using various exposures of the scene and comping them together in Photoshop manually (as opposed to trying to get a gamma/color mapping solution that is spot on at render time).

I figured we should render the image as a 32bit exr file then exposures can be ‘grabbed’ in Photoshop to piece together the image.

So, I have unticked ‘sub-pixel mapping’ and ‘clamp output’ and we are using ‘Linear multiply’ with a ‘Gamma’ value of 2.2.

If I render the image to the Vray framebuffer and save out the image as an EXR (default settings), open the EXR in Photoshop and heavily underexpose the image, I get very different results to instead telling Vray to save out a vrayimage file (though manually giving it the extension of .exr) upon render completion. Its as though the manually saved out file isn’t actually holding any more exposure information than a normal tga image, whereas the vrayimage (though with .exr extension) is. Underexposing the latter seems to keep the blown out areas blown out for longer.

Good grief, this is so confusing to write!

Why do I experience this?

2

I have also noticed this - using the 3DSMAX save function from within the VRAYFRAMEBUFFER to save an EXR has sometimes (but not always) clamped the exr.

Using the VRAY RAW IMAGE SAVE will ALWAYS work in my experience - never clamped, always perfect.

Just use this.

P.S. EXR’s should be in linear space, so having the gamma at 2.2 you should tick ‘adaptation only’ also, otherwise you will be messing the file up…

3

Glad you understood my post! Is this a bug, or is it intentional then? The problem with using save to vrimg files is that quite often I don’t set it up before I click render - as far as I am aware, you can’t save the image in the VFB to a vrimg file after it has finished rendering…or can you?

4

With a small Workaround you can. Enable VFB History, set the temp dir and hit save. You will get an vrimg of the vfb in the temp dir to (ab)use :stuck_out_tongue:

Regards,
Thorsten

5

Sounds OK - I have had the history thing set up in the past. This does seem like an obvious thing to be sorted out though - SP3 perhaps?

6

I think this is a 3dsmax issue, not a Vray one as it’s Max that is doing the saving.
Although I’m no expert and could be wrong…

7

Maybe check your default settings in the save dialog and make sure you are saving 1/2 float or full float exr files. I’m sure you are on top of it, but I have made that mistake before.

b

8

Have you tried saving out to HDR?
Because of these issues with exrs, we have been using HDRs instead with a separate Alpha as needed.

9

you mean these issues with Photoshop, not Exr :stuck_out_tongue:

Regards,
Thorsten