I have created a twilight skydome from scratch, in Photoshop, using only gradients. Now, I wish to create a companion HDR image for lighting, in Cycles (World texture). I know how to combine bracketed exposures, to create an HDRI. But, has anyone tried to create one from scratch, using gradients? I merely need to place a red-orange glow on the western horizon (key light), and have a much fainter cyan-blue glow coming from the rest of the sky (fill light) It doesn’t have to be pretty, as it is for lighting only, and it will not be visible in the scene.
In 32bit mode simply paint with brush/gradient values that express relative scene exposure values and thats it. HDR is not much more than bigger dynamic range. If you want a brightness difference of 50:1 between the orange glow and blue sky, either paint orange with values around 50.0 and blue around 1.0 or orange around 1.0 and blue around 0.02 and you get the relative difference. With exr, the absolute values are not so important because you can set the exposure in World shader. Exr has the same relative precision over the whole possible range of values so it makes no difference if absolute values are 50:1, 1:0.02 or 50000:1000
Thanks. It took a minute to figure out which 32-bit adjustments worked, and how they worked. I also had to add color samplers at key points, and set the reading to 32-bit, so that I could tell what I was doing. The “Exposure” adjustment worked really well, using the exposure and gamma sliders. “Levels” also worked, but in a rather unpredictable way. It took a bit of figuring to get the colors of the lighting right.
The only real problem was the noise in the rendered image. Is there a trick to reducing noise with this kind of lighting? (other than just throwing some insane number of render passes at it) Maybe, instead of using gradients in the lighting image, I could use solid patches of color?