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HDRI/IBL in Bryce….A New Approach

February 4th, 2008 Posted in Bryce-related
By now, most Bryce users have played with the HDRI/IBL sttings in the Sky Lab.  And we've become accustomed to the need for the "Spherical Probe" type of HDRI image in order for Bryce to play nice.  While there are some of these available on the web, as well as tutorials on how to make them, they remain a curiosity….we seem stuck in the "Shiny Reflective Sphere" stage, just as we first opened Bryce and put that shiny sphere over a plane of water.

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.  Shrinkwrap Function 

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:

Quality 256
Intensity 10
HDRI Effect 100

Now, what this does NOT do is cast true shadows.
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.

Nest came adding multiple colors in a box-like formation…trying to imitate the ambient light found in an enclosed room with different colored walls. I still need to experiment with how to lay out the blocks of colors, but this gives the idea well enough.You can see where the hdri image is very jaggy where the colors meet, due to the shrink-wrapping and distortion effects,….but just look at the amazing color blends that occur on the objects!!

In conclusion:
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!

  1. 5 Responses to “HDRI/IBL in Bryce….A New Approach”

  2. By firstmivan on Nov 30, 2008

    Thanks for an informative tute. I did not realise this information existed.

  3. By Rosemary Regan on Dec 7, 2008

    A new addition to the Bryce6/HDRI/IBL world are two new tutorials by Hans-Rudolf Wernli (aka Horo, in most Brce forums). Both tutes are in the mid-level to advanced range, but cover the detailed steps quite clearly.

    http://www.horo.ch/raytracing/sys/index_en.html#DocTop

    One shows how to make a really good outdoor spherical light probe from a Bryce scene, to use back again in B6 as HDRI input.
    The other shows how to make a cross-style panorama, for the same purpose.
    Each tutorial details the common flaws that can be avoided.

    Our thanks to Horo for the hard work done to promote the best qualities of Bryce! be sure to check out all his other Bryce-oriented work as well.

  4. By GMLAB on Jun 20, 2009

    Awesome information!! Thank you so much for this usefull tutorial about HDRI in Bryce.

  5. By anena on Nov 19, 2014

    Great article

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