To HDRI or not to HDRI, that is ...

[Metin_7]

... the question:

When does something have a high dynamic range? When I use a HDRI bitmap for (environment) lighting and reflections, the render immediately looks much more realistic, so I wouldn't want to depart from that anymore. When I add a VRay light for sharp shadows (especially when it is a colored light), often the realism of the render fades away again. So maybe this is a stupid question, but does the VRay light have a high dynamic range, or isn't this relevant for a direct light? And can I create a HDRI white card by using a white material and turning up the output of the diffuse or self-illumination (which one?) beyond a value of 1? As you can see, it's not really clear to me yet when something has a high dynamic range and when not. If any of you glossy car or atmospheric interior wizards can help me out, I'd be grateful. Thanks in advance!

Cheers,

Metin

[jujubee]

something has high dynamic range when it contains an extra channel with RGB. This extra channel specifies the strength of light (intensities) at certain points generated from the map. Think of it as a stained glass window with some dark and light varying colors filtering through. Certain materials will pass more light through.

I don't believe vray lights are hdri- though any 'light' can theoretically mimic the 'real world' intensity if you have an inverse square falloff applied to them.

The complimentary way to adjust your vray light for the scene in conjunction with hdri is to set your vraylight to have soft shadows in the checkbox rollout for the light. This is the closest approx ive had for a scene similar to the one you are describing. Perhaps there is a better way but this is the only one ive come up with thus far.

-juju

[Metin_7]

Thanks for the explanation! I have experienced that the Smooth Surface Shadows (or something like that) checkbox can in certain scenes cause artifacts on surfaces. I once had this and searched for an hour trying different GI settings before I discovered it was that shadows option that caused it. I believe the smooth shadows made an edge visible in an object or so.

Cheers,

Metin

[jujubee]

..err smooth shadows. I think I might have meant check 'area shadows' in the light paramters to get it to diffuse more properly...

[Metin_7]

Ah, yes. Area shadows rule.

[PATER]

of cause Vray-Lights are "HDRI"

turn up the light multipler and watch the reflection of the light on a simple dark-reflecting plane...

And yes... it's definately relevant for a direct light!

HDRI is everything that has information beyond the normal picture color range. Normally this is 8bit per channel = 255 colors. A 16bit per channel Image has more information but if the color on a certain picture is white, it's still white and that's it. With HDRI there is not a clamped color range but the information at a given pixel is described through a flowting point number... for example: 2.6. Programs that can handle HDRI now define a certain value as visible white.. (and/or black) let's say 1.0.
Our 2.6 pixel now appears white on screen but there's still more information behind it that you'll see in reflections or if the picture is used as a lightsource.

Hope that helps

[Metin_7]

Thanks Pater,

Did you already check out the new Color Correct version by Cuneyt Ozdas? It works in floating point values now, so you can now manipulate HDRI images with Color Correct. I wonder the following though: will an 8-bit white image become HDRI if you turn up the brightness level in the new CC?

Cheers,

Metin

[losbellos]

if it scales the low dynamic range image's pixel(simple bitmap) value into high, then yes. (same u can do in hdrshop scale pixel)
I'll check out the new color corrector as well. Great tool!

[PATER]

exactly losbellos...

and no, i didn't check the new color correct either, i'll do it as fast as i can!
(i'm trying mental ray right now, with the exposure control you have almost realtime control over the hdri illumination of your image... thats what i want in the vray vfb )

Thanks for the Tip Metin_7!

[Metin_7]

You're welcome!

Cheers,

M7