View Full Version : backdrop radiosity?

07-09-2005, 01:35 PM
How does one go about using backdrop radiosity? I assume you need to add a Textured Environment to the Backdrop tab, but what kind of picture are you supposed to use? And how does LW calculate light from a JPG or BMP which, unlike an HDRI, stores no light data? And finally, what are the advantages/differences between Image World (HDRI) and Textured Environment(non-HDRI)?

Sorry for asking such basic questions, but the LW manual didn't adequately answer my questions.


07-09-2005, 02:56 PM
Backdrop radiosity can be used a few different ways. If you click to Enable Radiosity, then change the Type to Backdrop Only, then the Backdrop Color is used (Window > Backdrop Options > Backdrop tab.) Lightwave defaults to this, and since it is usually set to black, you wont see anything happen when you hit render. If you change the colors so it is white, then you will see that your object is lit with an overall soft-surrounding white light.

If you click to enable Gradient Backdrop just underneath that, then Lightwave uses the four sky and ground colors to light your object. Having Gradient Backdrop checked overrides the Backdrop Color.

If you click on Add Environment and use Image World or Textured Environment, this again overrides the previos methods for illumination. Image World wants you to load a light probe image. These are images that look like they are a picture of a chrome ball with the environment reflected in it. The Image World plugin automatically undistorts this image and uses it to surround your environment. Image World gives you only a few basic options for using an image.

Textured Environment is a little different. You can still use images mapped to 'world coordinates', or you can use procedural or gradient textures to map your environment. It uses the same standard texture editor as if you were texturing the surface of a model. You can use layers to build up an environment. A good example of this is in your Scenes/Eki_SkyGen directory (I think these shipped with Lightwave). If you load one of these scenes, you'll notice that it is using the Textured Environment to create incredible skies from a combination of textured layers.

Standard 24 bit images can be used for global illumination, not just HDR images. HDR images tend to look better for reflections on surfaces because the dynamic range of the images is much higher.

07-09-2005, 04:27 PM
HDR Images dont store light data and in fact have nothing to do with lighting any more the any other image format has to do with lighting. HDR Images simply have a higher dynamic range and contains more image data then a standard 24 bit image format.
As Axis pointed out ANY image can be used to illuminate a scene or assist in illuminating it. HDR Images dont always necessarily result in more realistic or improved lighting or reflections. Like anything else theres always a bit of tweaking required to control how it effects lighting or reflections. 24 bit or LDR Images (Low Dynamic Range) can be cheated into behaving like HDR Images by using gradients. :)

07-10-2005, 05:23 PM
Thanks for that lovely and utterly coherent explanation. Reads like something that should be in the LW manual if it isn't already. Best of all, I finally understand how the different backdrop options work! :bday:

Thanks for setting me straight on HDRI. How do you tweak your HDR images? I tried using the HDR Exposure image filter in Layout, but tweaking any of the parameters caused excessive noise..at least in FPrime. :alien:

07-11-2005, 11:06 AM
If you use HDR Images for lighting I tend to reduce their size and/or blur them. Ill also sometimes use a skyball and image world/textured environment - one for lighting and the other for reflections.
Ill sometimes use HDR expose to reduce the brightness. You can also take standard 24 bit images and cheat them to behave as HDR Images by using gradients. :)

07-11-2005, 12:33 PM
or you can do the hdr in different forms depending on channel. which is good for simulating skin [you would need SSS to get full affect], can also for just about anything else.

The original map in all its glory [this is for the enviroment], a blured map for the diffuse [enviroment] it should be very blurred, and then a Specular map [enviroment] that is blured but is between the original and the very blurred diffuse.

Debevec's HDRShop can create the diffuse and specular map.

07-11-2005, 05:02 PM
Alternatively, you can simply do it in Image Editor by cloning the image and using FPBlur on it... no need for additional copies of the file.