6/26/2023 0 Comments Adyofspira terragen![]() That's the scale that everything else derives from. In the absence of atmosphere, a Terragen sunlight strength of 1 falling directly (perpendicularly) onto a diffuse surface with albedo 1 seen with camera exposure 1 produces a pixel of value 1 in the EXR. We just need to figure out the constant scalar to match the target of 2.43e9 nits. I've aimed to make all the ratios in Terragen physically plausible with default atmosphere settings, so the ratio of sun to sky luminance should be about right, and the surface of the sun should be the physically correct ratio to the illumination it provides. But it should be possible to work out the scaling factor with the information we have. QuoteLuminance values in Terragen are based on pixel values without any real-world units, because the camera exposure is also without units. Here is some info on real-world lighting equivalence for Terragen, quoted from Matt Fairclough, Lead Developer/Software Architect: Those HDRIs at SAStudios are created in Terragen 4. I don't really know how this can be measured accurately, without real world values. It claims that it has a dynamic range of 25-30 stops. Can you import a physical camera that measures shutter speed, aperture, and exposure? How can you render a cg sky in Terragen and mimic desired real-world measurements like lux values and sun to shadow ratios? At least to gauge the accuracy of the the cg sky. However, Terragen's rendering camera doesn't have a physical camera. This is better than most commercially available panoramic hdris because of the the technical limitations of phyiscal cameras (except if you use multiple ND filters). From looking at Terragen 4, it can render very dynamic hdris with a sun intensity that rendered unclamped and spans the whole range of a 32 bit float texture. I am researching a good way to create physically accurate hdri panoramas for Realtime rendering game engines.
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