Category selected: Mental Ray


Tip (3ds Max & Mental Ray) – Using environmental shader maps with mr Sun and mr Sky

Categories: 3ds Max, Mental Ray, Tips. Time posted: 2:51 pm, 4, Saturday, October, 2014

If you have tried to use an environment map within a Mental Ray material (say, you wanted it to emulate a scene being reflected off a mirror) while using the mr Sun and mr Sky set up, you would often find it to be rendered black, such as the example below. The black shaded areas of the building are meant to be windows reflecting an environment map, and unfortunately that’s not the case here.

fch_22_bad

Unsure on why it happens, but there thankfully is a solution to this odd problem. Go to the main menu and select Render, then Exposure Control (or press 8 on the keyboard). Navigate down to Physical scale and change the radio selection to Unitless. To get the environment map to show up, the number is required to be very high, which in my case was 10,000. Your scene is likely to be different, so it’s best to experiment by rendering the scene and determining which Unitless value works the best until the environment map isn’t too dark or too bright.

exposurecontrol_01

End result:

fch_22_m

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Tip (3ds Max & Mental Ray) – Self Illumination (Glow) materials noise issue

Categories: 3ds Max, Mental Ray, Tips. Time posted: 12:07 pm, 6, Saturday, September, 2014

(This is for when Mental Ray is the active renderer, doesn’t apply to Scanline)

I have noticed that when I use a Self Illumination material, it would sometimes leave noise within the scene, like the following image.

speckles_dirty
(Click for full sized image to see the noise issue)

As you can see highlighted by the circles, you see pin prick dots of the emitted colour. Not exactly a very desirable outcome.

A way to reduce the noise impact is to access Render Set Up (accessible through the main menu, Rendering -> Render Set Up) and then select Common tab. What we are looking for are the Sampling Quality roll out, which will have the Samples per Pixel (default would be Minimum: 1/4, Maximum: 4). By increasing the values of these units, we can soften the impact of the artefacts or noise issue to a more satisfactory level.

What does it do? Unfortunately it is a process that will take too long to go into depth, thankfully this website covers in depth on what we are dealing with.

Moving on, by increasing the Samples per Pixel from Minimum: 1/4, Maximum: 4 to Minimum: 1, Maximum: 16, the results are improved as shown in the following image:

speckles_clean
(Click for full sized image)

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Tips (3ds Max & Mental Ray) – Disco effect in your rendered scenes

Categories: 3ds Max, Mental Ray, Tips. Time posted: 2:31 pm, 11, Monday, August, 2014

Ever come across a disco effect in your rendered scene when using Mental Ray’s Final Gather in 3ds Max? Issue may also be described as speckling or spotty lights (visual example in the inserted image below). The problem may be more noticeable when you have light reflecting off a shiny surface, such as the metal used in the TV set below.

mentalray_disco_01

To access the Final Gather settings, open the Render Setup window via Rendering -> Render Setup, or by pressing F10. Once the window is open, navigate to the Indirect Illumination tab and then the Final Gather drop down.

One way of removing the bright speckling is to increase the Interpolate Over Num. FG Points in the Final Gather drop down.

Render Setup Dialogue:
mentalray_disco_02

In the television set scene shown above, the FG Precision Presets dragger was set to Low. To remove the lighting problem, keep increasing the value of Interpolate Over Num. FG Points until the the edges of the light disks are no longer noticeable. In the above scene, a value of 100 was enough, but it different scenes will have different values so it may take a bit of trial and error. What this does is to smooth out the edges of the light disks, such as those visible in the image above. Mind you, it may require a bit of trial and error to find the right number value before the light disks are smoothed out.

End result:
mentalray_disco_03

 

Just be aware: Increasing the number will smooth out the irregularity of the lights in the image, but won’t necessarily be an accurate representation of a real world scene since the number of photons emitted within the scene will remain the same. For a more physically accurate scene, it is advisable to examine the other Final Gather settings to achieve the results you are aiming for.

Additional Information:

3ds Max describes Interpolate Over Num. FG Points (source) as:

  • For each final gather point, mental ray interpolates (averages) indirect light values over the nearest N final gather points, with N specified by the value of this parameter, as opposed to points within the specified radii as with the alternate method. Increasing the value increases the smoothness of the result, and the required number of calculations, hence the render time (but not as much as you might expect).

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