Just a few quick notes. I'm overwhelmed with work so can't write my usual long answers.
- There is no "absolute" value that is "correct" for IBL intensity. It depends on how much light energy is recorded in the image, and as well how much ambient illumination you want from that image. A really dark image IBL image can be made into a very bright one by using a very high intensity, such as 300%. A very bright IBL can be made into a very dark one by using a very low intensity, such as 1%. The intensity is a multiplier, just like the "volume" knob on your stereo. When you turn up the volume, the music is louder, regardless of what absolute loudness it was recorded at. However, "loud" music is already loud even without turning up the volume. So, too, a "bright" IBL is already bright even at 10% intensity. The math is simple: illumination = IBL brightness times intensity / 100. Another way to look at it is this: When you use a camera, the correct shutter speed and f-stop will depend on how bright the world is, what your ISO setting is (or film speed) and how bright you want it to be in the picture. There is no absolutely correct f-stop or shutter speed. It depends on what you have and what you want. If I shoot in bright sun at 1/4000 second and f/36 on ISO 100, the photo will be dark. If I shoot the moon at 30 seconds and f/1.4 on ISO 3200, it will be so bright it will be pure white - no detail in the photo will be visible.
- A JPEG is not HDRI, even if you convert it to HDR format using HDR shop. An HDR image is, by definition, one with HIGH DYNAMIC RANGE. A JPEG is LDR, i.e. low dynamic range. So this talk of saving as JPEG and converting to HDR is silly.
- An LDR image can be forced to act like HDR by using a high intensity, above 100%. For purposes of IBL illumination, this can actually be good enough, even though certain individual intensities cannot be represented this way in a JPEG.
- IBL probes are those things that look like reflections in a sphere. However, probe images that were actually made that way are not accurate, just so you know.
- IBL images, whether HDR or LDR, are supposed to be in linear color space, not gamma corrected. Most LDR images are in sRGB color space and will not produce accurate illumination unless you anti-gamma correct them. You can do this in the light shader.
- Some HDR images are mistakenly being distributed in sRGB color space. Dosch has done this. Such lighting will lack contrast and be over-lit.
- If you're getting blown out white or yellow skin using ONLY the IBL, you have the intensity too high. If you cut it in half and its still bright, you still didn't go low enough. If you have to decrease it to 1% or less to get it to look normal, you probably have an sRGB image and you need to fix it.
Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)
