HDRI newbie questions

[Pg09]

Ok, this is more like a general question than a Twilight one.

Can someone please tell me when and why we should should use them?
(i'm mostly interested in architectural use)


HDRi lightning almost always give gives you (very) soft shadows. True or false?
Is there a way to control this softness?
The only way to control the the direction of the shadows is to rotate the the picture. True or false?
Do you ever combine cast shadows and HDRI lightning? How?


I tried to search the net for the answer but i only found tutorials about creating HDRis and using them in different renderers...

Thanks and

[Frederik]

Ok, this is more like a general question than a Twilight one.

Can someone please tell me when and why we should should use them?
(i'm mostly interested in architectural use)

Perhaps it would be a good idea to start off with a general explanation about what a HDRI is...

HDRI (High Dynamic Range Image) is a set of techniques that allow a far greater dynamic range of exposures than normal digital imaging techniques. The intention is to accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to the deepest shadows. The use of high dynamic range imaging in computer graphics has been popularized by the work of Paul Debevec.

And you can also find useful information at Wikipedia...

HDRi lightning almost always give gives you (very) soft shadows. True or false?

I'd say True to this...
Personally I've never seen hard shadows in any renders where a HDRI have been used...

Is there a way to control this softness?

There's really no direct answer to this question, since it depends on the HDRI and the render application used...

The only way to control the the direction of the shadows is to rotate the the picture. True or false?

True...

Do you ever combine cast shadows and HDRI lightning? How?

Not sure exactly what you mean here...
In most cases you will use a HDRI to "emitate" a light studio or a live world environment...

[Pg09]

Frederik, thank you for the answer.
In the last few days i read a few things about HDRi so i think now i understand the basics (hopefully)

I saw Fletch recommending HDRIs for architectural renderings (like in this topic: http://www.kerkythea.net/joomla/index.p ... &Itemid=76 )
but it looks like to me that if we use HDRi-s the result is always a "cloudy weather" render which is usually not what the clients are looking for.
(and actually it is not common at all where i live now )

So this is my understanding of HDRIs now, maybe Fletch can confirm/correct ?

Thank you Fred again!

[Fletch]

I don't recall recommending them for Architectural exteriors Although I've seen cool renderings done with HDR and exertior arch. renders. I've done a couple myself.

They are perfect for "studio" renderings... a car on a stage, an hourglass, a clock, an Ipod, etc. you know, stuff.
They could be used for exterior arch. renderings, but will not in my experience give you that "bright sun-shiny day" feeling... but I suppose that it would depend on the HDR you are using and the 'look' you are going for.

[Ecuadorian]

I see it this way:
With Twilight's Sun+Sky, you have two clearly distinguishable light sources: A sun with constant brightness across its radius, and a sky. This works well to simulate perfectly clear sunny days, but this model does not account for clouds, which also contribute to lighting. Depending on how dense the clouds are and how evenly distributed they are, the distinction between light from sun and light from sky blurs, and the model becomes not so good. Moving the "sunlight" slider to the right will not simulate a proper cloudier day, but only how the scene would look if our sun was much bigger. And this is when HDRIs shine: You can get a way better "partly cloudy" or "overcast" look by loading an HDRI spherical sky.

Please note that HDRI "light probes" (that is, HDRI photos taken with spherical mirrors) are a different beast from HDRI spherical skies. Light probes are meant to be used only for illumination, and not to be actually seen in your render, as they're often low resolution. You can find HDRI light probes (called "sky probes" in Twilight) that simulate the light inside a church, inside a studio, library, etc.

[Pg09]

Fletch, i was referring to the Mini Cooper thread over in KT forums (and somewhere else but i cant recall) , but it's ok i see what you meant.

Miguel, thank you, now I'm starting to get the whole picture...


Thanks guys!

[Fletch]

I was pretty sure you were referring to that thread, That particular thread is more about the 'objects' than the architecture, wouldn't you say?
and again, it's dependent on the 'look' one is going for, and the HDR used.

The thing about arch renders, you will generally want immediate and complete control of sun angle/shadows, so HDR is not great for this application... but again, depends on the situation.

Don't forget to look closely at Rafa's great tutorial on HDR and sphericals, globals, etc.