But it is time to move on, my friends.
Continuing investigations in HDRI lighting studies, leads me to a startling conclusion: ANY square-aspect image can be used in Bryce's IBL/HDRI input, as long as it is converted to an .hdr file. For purposes of these experiments, I began in Photoshop, made some color gradient images, took those into HDRIshop, converted them *directly* into .hdr, then used them –unaltered in appearance– in Bryce's Sky Lab.
After some investigation, here's what is happening behind the Bryce Sky Lab functions.The square aspect image is 'read' only in a circle that fits into the square…this readable area is then shrink-wrapped over the IBL lighting 'sphere' (an imaginary super-sphere which will surround your scene…essentially it is the 'sky'). The image information from the arced corners is discarded. The outer circumference of the image's circle is pulled down to a point on the opposite side of where the image's center will show. There is considerable stretching of the image, particularly noticeable where the 'backside' of the IBL lighting sphere can be seen.
But if you create an evenly colored square image, no distortions will be noticable. I created a circular red-white gradient …and made it into a .hdr file, and used it to be the only light in a scene. In the scene were a cylinder and a sphere, both colored flat white. I rotated the view to show how the gradient appears in the scene (if used as background) and how the lighting affects the objects. You can see where the white outer edge of the circular gradient has been pulled together into a small area on the 'backside' of the IBL image sphere. In these red-white images, NO added lights were used, the sun was turned off, and the HDRI settings in the Sky Lab were:
HDRI Effect 100
In the next set of images, for the first, I added a ground plane (colored white) and rendered with only HDRI/IBL; no sun or other lights in the scene. In the second image, I added a white-colored sun positioned roughly where the light was coming from in the HDRI/IBL image.Take a good look at the cast shadows now…. With normal 'sunlight' in Bryce, those shadows would be shades of black. But here they take on a red cast.
What we have with the HDRI/IBL function is a way to create image-based *AMBIENT* lighting. We no longer have to be confined to the single-color ambient choice in the atmospheric settings. Other lights *will* often be needed to create cast shadows (if they are truly desired for the render), but you can come much closer to 'real-life' lighting with your IBL functions. [In addition, though, you can *add* the single-color ambient light setting in the atmosphere settings to give yet another tint to the overall scene.]
I hope this experiment will give you the push to make experiments of your own in the Bryce Sky Lab! HappyBrycing all!