Search found 13 matches

by polyrhythm
Wed Mar 11, 2020 6:29 am
Forum: User Support
Topic: Colorspace and primaries
Replies: 12
Views: 1951

Re: Colorspace and primaries

There's some misconceptions here I'd like to clear up. By default, Blender puts you in the Filmic "Blender" color space - one made specifically for Blender. It is "wide-gamut" and supports plenty of dynamic range in the scene-referred values. If your only concern is that you're somehow trapped in sR...
by polyrhythm
Tue Mar 10, 2020 3:32 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

Maybe this is the confusion here? When we say EV 0 corresponds to an illuminance of 2.5 lux, I don't think it means that 2.5 lux should read as a RGB 255 white pixel, but as 0.18 mid gray?
Yep, that seems right to me.
by polyrhythm
Fri Mar 06, 2020 12:16 pm
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

If it helps, 2.5 lux results in "proper" exposure for EV0. Meaning, I guess, middle gray is middle gray? Illuminance is measured using a flat sensor; if the common value of C = 250 (unit: lux s ISO=lm s/m2 ISO) is used, an EV of zero (e.g., an aperture of f/1 and a shutter time of 1 sec) for ISO = 1...
by polyrhythm
Wed Mar 04, 2020 6:21 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

exposure / (fstop * fstop) * sensitivity * .65f / 10.f * powf(118.f / 255.f, gamma) which is coming from https://en.wikipedia.org/wiki/Film_speed. 0.65 is a factor depending on the transmittance T of the lens, the vignetting factor v(θ), and the angle θ relative to the axis of the lens. I don't kno...
by polyrhythm
Mon Mar 02, 2020 12:18 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

chafouin wrote:
Sun Mar 01, 2020 6:08 am
Please check you have that version of the file: https://github.com/LuxCoreRender/BlendL ... 7f9a8dc165
It is literally a 4 Pi multiplier now.
Ah, I see. The latest Github builds aren't picking that change up as of today.
by polyrhythm
Sun Mar 01, 2020 1:16 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

In that case, it looks like right now our 4*pi lumen point light is right on. It results in ~0.318 luminance on a surface one meter below. To go from luminance to illuminance is a multiplication by pi. 0.318 * pi = 1.0 (lux)! Unfortunately I am still seeing the discrepancy between that and a 1 cande...
by polyrhythm
Sat Feb 29, 2020 11:49 pm
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

UE4 has a visualize HDR setting that gives you lux, so I was using that to check values, but didn’t think of disabling the tonemapper to check visually too. I’m afraid my coworkers might start questioning my sanity once I have 10 renderers open with these boring point light tests. :D
by polyrhythm
Sat Feb 29, 2020 1:50 pm
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

There’s a lot of multiplies by 4Pi flying around in that file. I guess it makes sense since they’re unitless so they just take whatever the input is and assume it’s isotropic radiant flux. Still, my head hurts a little when it comes to cross validation, how are comparing and so on? Mitsuba has a rad...
by polyrhythm
Fri Feb 28, 2020 4:41 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

One more funny thing. I know, I must be getting tiring. As mentioned, the one candela point light results in around 0.256 "irradiance". If I switch it to 4Pi Lumens (one cd = 4pi l), I now get a slightly brighter result at 0.318. Close to pi, but maybe not a thing, given how close these all kinda ar...
by polyrhythm
Fri Feb 28, 2020 4:23 am
Forum: User Support
Topic: Light intensities and matching Cycles
Replies: 83
Views: 9186

Re: Light intensities and matching Cycles

Also I changed my light to a true point light (radius 0) and it didn't meaningfully impact the resulting irradiance result. From the other thread linked, I can see that the current irradiance implementation has not officially been verified or tested against any known good results, so I'll treat it a...