How can I render redirection of metal blinds using photon map

Recently I was reading “daylight simulation with photon map” wrote by Roland Schregle, and found a rendering picture of Y glass’ redirection as following,


I also want to render the redirection of metal blinds referring to the example, is there anyone who have the example files of Y glass’ redirection rendering or could provide some suggestions?

I tried to model the beam with spotlight primitive but I can never get the beam as shown in the picture.

Thank you!

Hi Yongqing,

my memory’s as hazy as the mist in that rendering, but I’m pretty sure I used a very narrow spotlight. I think the parameters for the mist matter more than the spotlight, since too high an extinction can perturb the beam. I’ll look for the relevant files in my archive.

Alternatively, this effect can also be achieved by placing a bisecting plane perpendicular to the Y-glass, and omitting the mist entirely. This may give you the desired effect faster, infact.

The “look” of that figure is probably also dependent on the tone mapping. I may have used pcond with fixation points outside the main beams to reduce the contrast and emphasise the weaker, secondary beams, notably in the right figure.

Will get back to you on that once I find the original data. It’s been a few years.

Best regards,


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Hi Yongqing,

I found the relevant files, and it turns out I infact went straight for the alternative approach with the bisecting plane, and not mist, since this is easier to control. My memory served me right on the fixation points passed to pcond, which can be selected via ximage’s -op option. Unfortunately I didn’t store the points, but they were probably placed along the main and secondary beams.

You can find these details in the original files and a script I used to generate these renderings:

Hope this help. Happy rendering!


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