What in the frippin' frap are "light probes"?
mavante
Posts: 734
"Probes"? Seriously? I thought that was something used by hostile of-world aliens during abductions.
I'm endlessly looking for more and better ways to light up Iray scenes, and it seems that iRadiance has made a crusade of churning out package after package of "Light Probes" (they have like seven of them in the store)—but I have searched through all of their product pages in the store, and I cannot find a single word anywhere about how they are used!
Lord knows there is lots and lots of hoo-hah about how wondrful and perfect they are—and they sure ought to be looking at their prices—but not a whisper or even a hint of what you DO with them.
I have searched Google for some kind, any kind of tutorial or discusstion about what a "light probe" is, or how to use them. Nothing. Nada. Zip.
Do you have to be in some kind of secret society, and know a handshake or arcane word code to be allowed into the inner sanctum sanctorum of the Ministry of Light Probes?
If anybody knows anything about these products, and has used them, can you— Well, um, shed any light on this? (I tried, but the pun was almost unavoidable.)
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They are HDRIs.
Light Probes are image based lighting to give backgrounds, mostly, and lighting that matches the scene. Basically they are HDRI Environment Maps, you double click on the icon and it loads into the Environment Dome of Iray..
So why didn't they just say they are HDRIs?
From the responses so far, I guess they are essentially useless for lighting indoor scenes (but stay tuned)—unless somebody says otherwise.
Of course in the dense Daz marketing jungle, this is made even more tangled, more opaque, and more confusing by the presentation of a product in the store named Iray Light Probe Kit, which is ... [LEWIS BLACK] B-B-B-B-B SPECIFICALLY FOR INDOOR SCENES!!!! MAKE UP YOUR MIND!!!!! [/LEWIS BLACK]
AFAIK that is more a ghost light set, in which the word "probe" is used for the ghost light globes... Can't say I'm sure why the word "probe" is used though.. when looking for a definition what "probe" stands for I came only up with these two:
1. a blunt-ended surgical instrument used for exploring a wound or part of the body.
a small device, especially an electrode, used for measuring, testing, or obtaining information.
2. a thorough investigation into a crime or other matter.
"a probe into city hall corruption"
Not much about light there... but I sometimes get the feeling DAZ artists do their own definitions (or work with botched translations... thanks google ^^)
Yes, that's correct about the Iray Light Probe Kit. At least that one is clear on its product page about what it is, how it's used, and what it does. It's evident not only in the description, but even in the supplied images. Even with that one, though, the use of the word "probes" is pretty silly, and even sillier given that the light sources are globes, not probes. What, are they going for Cockney rhyming slang? And as you so correctly point out here ... .
Exactly. They may as well call them "Light Skillets." It would make as much sense.
https://www.daz3d.com/forums/discussion/comment/1567581/#Comment_1567581
A light probe isn't just an HDRI it can have other light elements built into it. The Light Probe Kit seems to be spheres set to various emissive settings to be placed where needed, I don't have it but that is what it looks like reading the details on the store page.
What is a Light Probe
A light probe image is an omnidirectional, high dynamic range image that records the incident illumination conditions at a particular point in space. Such images were used in the paper Rendering Synthetic Objects into Real Scenes: Bridging Traditional and Image-Based Graphics with Global Illumination and High Dynamic Range Photography at SIGGRAPH 98 to illuminate synthetic objects with measurements of real light, and later in a SIGGRAPH 2000 paper to illuminate real-world people and objects. Two of our animations, Rendering with Natural Light and Fiat Lux demonstrated the use of image-based lighting. The commercial product LightWave 3D v6 was the first to support image-based lighting in 1999 and the technique is now commonly supported; see below for links to some sample renderings made using our probe images. Some of these images were assembled from high-dynamic-range panoramas, others were acquired by taking one or two high dynamic range images of a mirrored ball (see Reflection Mapping).
Light Probes are a type of HDRI which are used for lighting as opposed as environmental HDRI's which are used as backgrounds and their lighting is incidental. Why "light probe:? Most of them are simple mono color backgrounds with an HDR bright spot or geometric figure (the probe). In an enviromental HDRI, the light source can be something diffuse light brightly lit clouds which only produce a general diffuse light. The products in the store tend to be light probes while HDRI's in freebie websites are often enviromental.
From the gaming world: https://docs.unity3d.com/Manual/LightProbes.html
I have something similar from Octane render and iClone I plonk into the iray environment sometimes
they are rather plain looking with gradients blobs of light equally spaced or soft focused blury indistinguishable images and quite small but produce quite nice shadows and lighting and in my case fast without other lighting for animation.
The term "light probe" itself is derived from a physical object that is sometimes used to obtain the lighting information. To obtain an image of a total circular or spherical environment one can put a camera on a tripod and take pictures in all directions then stitch the images together. This is laborious, time consuming and sophisticated but can obtain very high resolution images if enough photos are used to cover the area.
Alternatively, one can put a spherical mirrored ball (a "light probe") in the center of a scene and then take a close up photograph of the reflections in the probe from at least two orthagonal angles (90 degrees apart) Then using software and image editing techniques you can stitch the images together. This is relatively quick but has several disadvantages.
The fidelity of the light probe's reflections depends on the quality of the surface of the mirrored ball, and because the surface is fragile and subject to scratches and fingerprints, an entire spherical ball polished to the same accuracy as a lens would be expensive.
Also, to avoid having to have a large ball (eg: 8 inches) to photograph, one could use a smaller ball (2 inches) but requires a closer camera or tighter zoom. A closer camera causes the camera and photographer to occupy a larger percentage of the image.
Tighter zoom affects resolution and image stability (eg: in windy conditions).
HOWEVER, if you're only interested in light levels and not image quality, a light probe is a cheaper and faster method than direct photographs of the environment if you give up the fidelity of a highly polished glass or metal ball and use a less accurately polished silvered plastic ball as your light probe which can be easily replaced when damaged.
The thinking among you who are not familiar with the light probe technique might be wondering, how do they get the camera and photographer out of the spherical images?
That, dear readers, is a secret sworn by all spherical photographers, to take to their grave.
Also, I believe that light probes are used in the movie industry photographing "flat" images. It's quick and easy to temporarily insert a light probe on a stick into the view of the camera and capture a single hemispherical image which can then be used to quickly extract low resolution illumination information from all directions visible to the camera.
The Light Probes you mentioned (iRadiance), as stated on the product page, are just HDR maps. You use them exactly the same as your normal HDRI enviroment, but preferably with "Draw Dome" set to "off" (unless you really want that weird looking background in your pic). You can use them indoors, but that would require to for example remove the ceiling or some walls to let the light in.
If you have photoshop or any kind of software that can tackle .hdr and .exr images, you can make your own HDR "light probes"
Thundorn Games on youtube has an awesome tutorial:
https://www.youtube.com/watch?v=bz86g_5WNoo
If you can't afford photoshop, I recommend Affinity Photo - it costs like $50 for a lifetime license and can read PSD files :)
Thanks everyone for the great explanations, I was wondering about that term too!
A light probe is what you get from an alien on your first abduction.
Imagine aliens that need lots of light, because...
Damnit, just noticed Cybersox's.
And the second time it's a not quite so light probe? Or a heavy probe?
Does it cure viruses?
only if UV
I can only imagine what an internal sunburn feels like, but it's probably on par with the alien probe South Park's Cartman experienced.
To bring this discussion back down to Earth (heh): In response to all the "I'm an expert" explanations in this thread, I still say, emphatically, that the name is a misnomer.
These products are not probes; they are the output, the product, of having used a "probe" to gather and record light information.
There is almost an exact analog in the world of audio. Technicians set up a special microphone(s) in an audio environment (such as, e.g., a cathedral), initiate a sharp loud sound, and then "sample" (record) the echo/reverberation reflections and responses of that environment. Those results are processed a certain way, and are packaged and sold. Recording engineers can then selectively dial in those results to an audio recording, perhaps recorded in a studio, to create the illusion, with reverb and echos, that the recording was made in that "sampled" location.
But guess what: Those products are not called "microphones," because they are not. They are the products resulting from a particular technical use of microphones.
Depends upon how "easy" the aliens thought you were. It's kind of like the baseball analogy and if you get to the third abduction, it's assumed that all of your bases belong to them.
Naw. I've never heard any reports of aliens sticking a microphone up anyone's anything.
so this takes HDRI images?
No. Only full-motion video.
But does it have a microphone?
Nice explanation.
Interesting side note about an impulse signal technique for obtaining information. When I was working at the Mitre corporation, (a government technological think tank in Washington, DC & Boston) one of the projects I was deeply involved in was using a radio impulse to measure the transmission distortions of radio waves through the atmosphere. If you've ever listened to a long distance AM radio signal you know it's full of pops, whistles, clicks and frequency warbles. These are caused by the radio signal bouncing off of the various layers of the atmosphere as it finds its way from transmitter to receiver. The layers are turbulent and vary from one microsecond to another. This scrambles the signal in inumerable ways.
Our project was to send a series of radio impulses (very short bursts), through the air and measure the way it was distorted when received. Instead of receiving a clean single frequency narrow pulse, the signal gets spread over time and frequency and looks a mess. The idea was that if the transmitter would intersperse the signal with impulses, or co-transmit impulses on a nearby frequency, then with computers we could compute an "inverse transform" and apply it to the received signal, millisecond by millisecond to reconstruct the original clean signal. Theory is good, but practice is difficult. Boston was handling the actual radio transmission tests (they had the radar experts up there). The Washington, DC division's part was to build a dynamic digital filter that would squeeze the scattered signal back into a reasonable pulse. Also, the filter was used by us in a simulator to test the concept in the laboratory in a radio isolated SCIF. The filter could be used to break a clean pulse into copies of actual recorded transmission experiments from Boston. The dynamic digital filter was amazing and worked quite nicely. My part in the project was to write the multi-processor, multi-process operating system and program the custom built multi-processor computer and write a driver for the dynamic filter.
This was in the early 1990's so this technology was leading edge at the time. By varying the Fourier Transform coefficients applied to the filter millisecond by millisecond we could generate a dynamically scrambled signal from a clean input pulse or take a changing scrambled signal and reconstruct the original static impulse. We played with it and generated simple mathematical distortions of the signal such as doppler effect & clipping. So, the device worked in the lab. However, at the time, the three micro-computers involved (3 separate single board computers boards each with a Motorola 68030 CPU chip. The boards were housed in a VME backplane chassis in a multi-processor arrangement sharing a single common memory board). The system worked but the processing was too slow (by 1000 times) for real-time use in the field. In the lab we were working with recordings of signals for which we had pre-calculated the inverse-Fourier transform coefficients, but we had proved the concept. The other major problem was the real-time calculation of the inverse-Fourier transform to be applied to the filter. Again, computers were too slow, even using three processors in parallel. Things have changed in the last 30 years so I suspect that if not already in use, it is again a viable idea.
Actually, a similar technique is already in use in telescopes where they shoot a laser beam into the sky and adjust small areas of the mirror to bring the dynamically jumping laser spot back into a single point. This makes the image of the stars clean, moment by moment.
So would you say that we should make the extra effort to find tinfoil and pay the extra cost, or is aluminum foil just as effective at blocking these radio waves? I've read differing theories.