32bit renderoutput - what's the dynamic range?

[MANUEL_MOUSIOL]

I'm wondering what the dynamic range of vray is when outputting 32bit images.
Its not endless obviously so there has to be something to evaluate like an Ev step range.
I always do proper exposure but it would be helpful maybe to know how far things can be pushed with exposure in post ..

[vlado]

The full range of 32-bit floating point numbers is quite larger, but the reliable is from around 0.000001 to 1000000. How far you can push things in post depends on other things as well - f.e. the noise level of the image.

Best regards,
Vlado

[MANUEL_MOUSIOL]

Ok and what else? Let's say noise level is 0. 0001. How does dynamic range compare to photographs?

[vlado]

I don't really know. Digital sensors don't have a whole lot of range, but it would be best to check with the specific manufacturer. Film obviously has no high dynamic range at all.

Best regards,
Vlado

[MANUEL_MOUSIOL]

That's not true. Modern cameras can have an amazing range. A7RIII has 15 ev stops eg. Film can also have around 14 steps.
We could compare the renders to one shot photos or to hdri, which could have 20 and more ev stops.
How many ev stops does a noiseless vray render have?

[vlado]

Of course, the camera itself has an amazing dynamic range. But once the picture is already taken and the colors burnt into the final pixels/film place, it's done. If an image is overexposed on film, you can't bring any of the detail back.

Best regards,
Vlado

[MANUEL_MOUSIOL]

With a range of 14 steps you can overexpose a little without a problem but obviously there are limits.
I am interested in these limits when it comes to vray though. ..

[vlado]

Well, in terms of actual exposure levels, there is no problem to go as far up or down as you want, V-Ray doesn't clip or otherwise remove any range by default. The only issue is noise, which might become more apparent. It depends on what you would find acceptable. If you expect to brighten up the image a lot, then you might need to render with lower noise threshold. If you intend to compress the colors, then you can probably do with higher noise threshold. I guess a rule could be that for every f-stop that you want to brighten up the image, you will need to reduce the noise threshold between two and four times.

Best regards,
Vlado

[MANUEL_MOUSIOL]

Ok that's an answer!

[MANUEL_MOUSIOL]

So a noiseless render would be full dynamic range from total darkness to total overexposed whiteness with everything in between as much as I want..
Great thanks

[^Lele^]

So a noiseless render would be full dynamic range from total darkness to total overexposed whiteness with everything in between as much as I want..
Great thanks

Besides the little detail that a noiseless render would take (literally) forever, no matter the computing power, sure. ^^
In practice, one establishes the range of possible EVs a Post process can play with, and tries to clean up noise taking those variations into account.
Typically those are in the order of one to two stops up or down, as anything else makes the rendertime too big (to get a noise level looking clean when exposed up), and is worth re-rendering to target exposure.

[MANUEL_MOUSIOL]

I had this job where I was composting lightselects and by client request the contrast in the process changed a lot...and really drastic. With noise it became ugly quickly and I had to re-render and de noise, but I needed a neutral exposure to stay flexible. But it made me wonder how much is really in there to work with...

[^Lele^]

For each stop up, halve the target noise threshold.
Not perfect, but usable, empirically.