Light probes. . .

cclesue

What the heck are light probes as opposed to any other kind of lighting?

Horo

A light probe is a spherical high dynamic range image (HDRI) which has an output hugely exceeding what an ordinary image can produce. The dynamic range of a picture is 256:1 at best, an HDRI can have millions to 1. Obviously, such an image cannot be displayed but there are several methods to compress the dynamic range so it can be displayed. However, a render engine can exploit that high dynamic range and thus light the scene. This is called image based light (IBL) and it needs a light probe.

prixat

The term never caught on.

It was intended to differentiate the HDRI that we use, from the what photographers think of... a series of exposures tonemapped down to a Low Dynamic Range... which photographers still insist on calling HDRI.

Horo

I think the term light probe was first used by Paul Debevec for spherical HDRI panoramas in the Angular Map projection at Siggraph 1997.

fastbike1

No. In photography a HDR image is created from a series of images taken over a range of exposures, each image typically separated by one stop of exposure. The final exposure isn't "tonemapped down to a low dynamic range" whatever that means. From a photographic perspective, 5 stops of exposure will typically be enough to accurately display a scene where a single camera expoure would either show part of the scene as completely blown out or completely black.

Calling such a composite image HDR is legimate for a photograph. 

prixat said:

The term never caught on.

It was intended to differentiate the HDRI that we use, from the what photographers think of... a series of exposures tonemapped down to a Low Dynamic Range... which photographers still insist on calling HDRI.

 

LeatherGryphon

I believe technically, a "light probe" was originally a physical object.  A spherical mirror that was inserted into a 360 and/or spherical scene.  The image in the mirror was photographed close up by a normal flat camera from multiple directions and the separate images combined and edited in such a manner as to remove the spherical distortions and to edit out the unavoidable side effect of capturing the camera and photographer.  Rather ingenious method to make the camera and photographer disappear.

Subtropic Pixel

Well, I'm so glad it's about "light" the noun and not "light" the adjective!

Because at first, I was thinking...aluminum probes?   

Sorry, I'm bad today.  Very very bad.  Hehe...

 

prixat

fastbike1 said:

No. In photography a HDR image is created from a series of images taken over a range of exposures, each image typically separated by one stop of exposure. The final exposure isn't "tonemapped down to a low dynamic range" whatever that means. From a photographic perspective, 5 stops of exposure will typically be enough to accurately display a scene where a single camera expoure would either show part of the scene as completely blown out or completely black.

Calling such a composite image HDR is legimate for a photograph. 

prixat said:

The term never caught on.

It was intended to differentiate the HDRI that we use, from the what photographers think of... a series of exposures tonemapped down to a Low Dynamic Range... which photographers still insist on calling HDRI.

 

Tonemapping "up" and "down" is my own term. 

When I combine bracketed exposures (tonemapping). I can combine them up to a 32bit exr file or down to an 8 bit jpeg.

...but jpeg or png files etc. are LDR files, its misleading, but understandable, that photographers call them HDR because of the method used to create them.

As Horo mentioned earlier, it was Paul Debevec who first tried to introduce the term 'Light Probe' for CGI, seperate from whatever photographers were naming things. A quick bit of google backed hindsight, shows it was not necessary. The search results are all about the kind of HDR we use in CGI.

(Give that another year and all 'HDR' search results will be about televisions!)