Free Sky Hdri

[tlehnhaeuser]

Free SKies HDRI

http://www.evermotion.org/index.php?unfold...nfold=exclusive

 

[Guest erindell]

Nice! Thanks Tom

[Guest EricFoy]

Very interesting sky shots. Resolution isn't very high, though.

 

This brings me to the topic of HDR... I notice that a JPG produces a very nice 3D background, whereas an HDR appears "overblown." I understand that the HDR format images contain something like 100 or 1000 times the dynamic range of light compared to a JPG.

 

IronDUDES: What is the best way to set up the environment for rendering? Can IronCAD actually use this High Dynamic Range of light intensities?

 

As a side note, the CG industry is currently failing to clarify the meaning of HDRI, as it has become a moniker to indicate all kinds of 3D projections and panoramas. So is IronCAD really able to use HDRI? Gimme da scoop!

[Bryan Cargill]

Yes, IronCAD's new renderer really does make full use of HDR images. It can use them as backgrounds or textures. It actually renders every image in an HDR format (you may choose to save in a typical LDR or an HDR format).

 

First, lets start with a description of the images:

 

Typical 24 bit low dynamic range (LDR) images are made up of Red, Green, Blue values in the range 0-255 (1 byte [8 bits] each). These are "24 bit" images becasue 8 bits Red+8 bits Blue +8 bits Green = 24 bits total. Theses RGB values can only represent a small fixed amount of intensity variation as they are limited to the range 0-255.

 

This is in contrast to high dynamic range (HDR) images. These images are represented in different formats-- but the general idea is to use floating point values for the R,G,B intensistes. So, instead of a single byte (0-255), an HDR image might use a 4 byte (0-4,294,967,295) floating point number. This allows for much higher precision and higher range of intensisties.

 

What does this actually mean to a user?

 

It means a good HDR image can precisely specify very smooth gradients and subtlties.

 

It means that areas of the image can be 'brighter than white.' You may adjust the exposure of HDR backgrounds inside IC. As the exposure is lowered the image gets darker-- but unlike LDR images, you will notice an HDR image does not get darker uniformly. Very bright areas (like the sun) will remain very bright, even as the rest of the image gets darker.

 

When it comes to global illumination (GI) HDR images take on special significance. In GI, the background is used to light the scene. These very bright areas (outside the range LDR images) accurately represent very bright lights in your scene. Without HDR, GI would be very limited and dull.

 

It is important to note that your monitor must eventually display these images. So eventaully things get mapped back to a LDR RGB format for display. And, if you save to an LDR format (BMP, JPG, etc) the image is mapped back to LDR RGB format. This process is known as tone mapping. Ironcad only supports one simple form of tonemapping based on an exposure and gamma setting.

 

As far as setup is concerned-- I would recommend using HDR background images if you are using Global Illumination. If not, then I wouldn't worry very much about the format of the background. If you want the ability to modify exposure and gamma settings in the future, I'd save to an HDR format. IF not, then use a familiar LDR format.

 

To control the "washout" I would recommend playing with the background exposure as well as the gamma/exposure adjustment after rendering. One enhancement that would help in this regard would be to allow different images for Global Illumination and for background renderering. You might use a low res, bright, washed out HDR image for lighting- and a highres jpg for the background appearance.

 

 

 

 

 

 

 

 

 

[Guest EricFoy]

Bryan:

 

Thank you for taking the time to offer this excellent and informative response.

 

...And your final paragraph gets right down to where I'm heading!

One enhancement that would help in this regard would be to allow different images for Global Illumination and for background renderering.

Any plans of implementing this capability?

 

As an alternative approach, how about having the renderer "match" the exposure and gamma of the HDR background to approximate those of the subject.

 

Also, LDR images do make nice reflections, so how about the ability to load three separate backgrounds - one for background image, one for background reflections, and one for GI. The latter two would end up superimposed in the reflections on the subject. All three should have their own intensity or gain settings.

 

Does this make sense?

[Cary OConnor]

Hi Eric,

 

Why would you not use the background image as the reflection image? In other words, why would they need to be different?

 

Cary

[Guest EricFoy]

I think the most common case would simply involve using the same image, but with individual gain settings -background brightness/gamma, and reflection brightness/gamma.  But I'm thinking I could also come up with some really cool effects, like...

1. Set the reflection environment with an image that is a chromatically skewed version of the background image, with, say, altered gamma and whatever else. This may be an easy way to simulate a paint that has a non-uniform chromatic response curve.
   
   
   
   • Actually, I'd like to be able to set color channel reflection response on a per channel basis for any given material (Smart Paint function). This may seem like a more logical approach, though the global reflection environment would also be nice.
   
   
   
   
   
2. One may want to render, say, a car looking out of a garage into a foggy meadow.  Then you could load the interior of the garage as the reflection environment, and the foggy meadow as the background.


3. Render your car in a city park with reflections of the Swiss Alps in the hood.


4. Use a perspective-calibrated 2d background (for exact, precise placement of your rendering subject) in conjunction with a suitable 3d reflection environment (for general realism, which is far less dimensionally demanding).

 

[Bryan Cargill]

I can't speak for exactly when the enhancements to background/GI image might appear-- but it is on our radar.

 

You may use a unique image for reflections in an existing (albeit painful) way. You may specify an image to be reflected from the "Reflection" tab of the surface finish. There is a "Reflect Image" option that allows you to browse for an image. A single global option would be much easier if everything in your scene needs to reflect something other than the background.

 

Here is an example- the blob on the left is refelcting a winter scene while the blob on the right is refelcting a desert scene (that is also the background):

 

[tlehnhaeuser]

I was going to learn Chinese, however since the inception the new rendering engine I see I will have to take a course in "Renderease".

[Guest EricFoy]

Bryan:

Yes, I have done the "reflect image" thing before, but it unfortunately gives me no control as to how the reflected image will be located or scaled... unless there's something I don't know there.

 

Anyway, thanks for your consideration of my rather eccentric requests.

At the front of the line would be a way to control the "compression" of background HDRI into a typical LDR image. I think the full HDR dynamic range is certainly useful and desirable for the purpose of lighting the scene. However, the rendering of the image into a typical LDR space seems lacking in the current renderer. I fully appreciate the fact that the final rendering contains an HDR range of values (adjustable through the "Adjust Tone Mapping" menu), but I'd like to be able to control the Exposure and Gamma (and dynamic range compression) of the background, independent from that of the rendered subject.

 

Does this make sense?

[Bryan Cargill]

No, there is no control over the details of the reflection-- your only option is to modify the image.

 

Yes- that makes perfect sense. We could offer more options to control tone mapping of the background. I think the best answer may be to just allow users to specify different images-- then you will not be limited to only built in IC image processing.

 

In the interim, you do have the ability to adjust the background exposure. This will change your lighting some but you should be able to roughly compensate with the GI power.