How to make a rectangular light in mental ray?

#21

Wow, well that pushes me more towards the opinion that MR is indeed incorrect, and that Vray and Iray are more accurate.

#22

for me look the mr portal light, the same as iRay rectangle light. But all the lights generate not a harmonic light emitting.

#23

Hi thorsten, thanks for putting the files and images up but unfortunately I can’t download the .zip file and can only see half of the images. The place where you are hosting the files is really slow and keeps cutting out mid download.

#24

hi mike,

i can download the file without problems, it comes directly from my website.

#25

Ah yes, it’s working now, many thanks for the setup, I’ll get studying it!

#26

Hi Thorsten, I couldn’t get the mia_portal_light Shader to work. If i enable it in the kight shader dialog, the light emits dark [no light] do you do any setup on the portal light shader map. Also where did you get the architectural environment portal you have in the sample files. {Is it some other hidden string]

Thanks

#27

Quote from Master Zap:

'Basically, the distribution of light from a flat plane can be calculated properly by taking samples and taking the traditional distance-squared for each sample. While this works, it yeilds a totally horriblke amount of noise that you need to turn up the samples to high heaven to get rid of.

The portal is designed to be smooth, and approximates the “sum of an infinite set of distance squared to every point of the light” with an approximation, such that it should have no noise created by sampling (outside of the inevitable noise caused by the cosine of the angle to each sample).

This algorithm is a bit of thumb-and-forefinger and is not totally accurate, and especially on a long-thin light it apparently breaks down a little bit. Note that this algorithm is only actually applied to light close to the lightsource itself, anything further smoothly interpolates towards a traditional distance-square based calculation (since the noise problem goes away at any significant distance).

So the light may be a little bit off in the extreme nearground, but it is specificaly designed for smoothness. At any distance (e.g. at a distance of about the longest axis of the light), it is accurate.

That’s the idea anyway

/Z’

#28

Well vray seems to have no trouble doing it correcly without the mentioned horrible amount of noise, so… :shrug:

#29

I tested on mental ray 3.9.1.36 maya 2012,and found that area light is ok.

It seems strange.

#30

That’s because it’s a 3ds Max “feature”.

#31

thank you for your reply,Jeff.

I watched your video,and found that using vray maybe the real solution.I wonder whether this feature is fixed in the later version,as I noticed you were using max 2009.

For I’m a maya user,I got a further test in maya 2012 and found some interesting:a reverse reasult with 3dmax.

I posted a test here,and looking forward to your reply.
http://forums.cgsociety.org/showthread.php?p=7497780#post7497780

regards.

#32

No, it’s not fixed as of 3ds Max 2013.

#33

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