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So what's the deal with night skies?

seachnasaigh

seachnasaigh

Energetic
@Dakorillon (IMArts) An HDRI doesn't need to be a spherical pano. It could be a closeup still life shot of Waterford crystal vases catching sunlight through a window. It doesn't need to be generated by a camera, either. The sky HDRIs I've made were rendered in Vue; you simply set the render engine to map entire range and export as HDR or EXR. The file size is ~100MB.

For purposes of using a regular JPEG on a skydome as a light emitter, you could exaggerate the brightness range by math, such as [sky pic] to the 5th power, then multiply that result by 30 or so, and using that as the emission/ambient strength.
Exactly how to accomplish that depends on what render engine and material system you're using.

I don't claim it's as good as an HDRI, but it allows you to use a much greater selection of skies. A poor man's substitute, so to speak.
 
Ken1171

Ken1171

Esteemed
Contributing Artist
Dakorillon (IMArts) said:
So, if I created a picture with 16 or 32-bit depth and saved it with that information (.tga? .jgp? .tiff?) , then, even though it wasn't a photo, it would still be HDR? Basically, can anything other than photos be HDR?
Click to expand...

No. It has [ideally] to be a combination of color depth and the multiple exposure shots. Otherwise it wouldn't be "High Dynamic Range". It would "Narrow Dynamic Range" instead. The multiple exposures widen the light sampling range, which is what benefits image-based lighting. However, HDRI doesn't have to be a photograph. It can be created with paint programs or rendering that support raw image formats. But if we save this as, for instance, JPEG, the color range will be compressed and loose most of the information. JPEG is confined to a narrow range of colors comparing to RAW. It's very important to save the image in the appropriate file format, where the most popular are HDR and EXR. Those were meant for this purpose.
 
Dakorillon (IMArts)

Dakorillon (IMArts)

Dances with Bees
Contributing Artist
Ken1171 said:
No. It has [ideally] to be a combination of color depth and the multiple exposure shots. Otherwise it wouldn't be "High Dynamic Range". It would "Narrow Dynamic Range" instead. The multiple exposures widen the light sampling range, which is what benefits image-based lighting. However, HDRI doesn't have to be a photograph. It can be created with paint programs or rendering that support raw image formats. But if we save this as, for instance, JPEG, the color range will be compressed and loose most of the information. JPEG is confined to a narrow range of colors comparing to RAW. It's very important to save the image in the appropriate file format, where the most popular are HDR and EXR. Those were meant for this purpose.
Click to expand...
Ah, slowly the understanding creeps in! Thank you again for your explanations. I'll have to experiment more.
 
Ken1171

Ken1171

Esteemed
Contributing Artist
If HDRI were about sound recording, each exposure would provide instruments in a different frequency range, like the bass, mid-range and treble knobs in an sound amplifier. When all frequency ranges have been covered with additional exposure shots, we will have a full orchestra. We then save all that information in HDR or EXR files, so nothing is lost. In other words, HDRI is the Hi-Fi of images, which suits the purpose of IBL with additional realism. :)
 
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