Photorealistic Diamond in Maya- Physical approach

Rendering a photo realistic diamond in Maya is little bit trickier. If you use Mental Ray renderer you will get a closely photo realistic render of the diamond. But due to the lack of advanced rendering algorithms such as dispersion we need to cheat the effect. Remember we already modelled and rendered a photo realistic diamond in Maya using non physical approach. I.e. we cheated the look of the diamond with some tricks. If you are not aware of that trick you can watch the full tutorial here. That method is useful for rendering a large number of diamonds. But if you render a diamond very closely the above tutorial won’t work that much. You need to add real shadows, caustics, dispersion, reflection and refraction.
In this tutorial you will learn to light and render a photo real brilliant cut diamond in physical way. I used Zap’s mental ray blog technique to create this tutorial. I used my own steps and values to create a realistic look for the diamond. If you want to know the real theory behind the rendering of diamond I recommend reading Zaps blog.
We are going to render our diamond in a real way. First of all you need to model the brilliant cut diamond in Maya. I recommend watching my tutorial on photorealistic diamond in Maya. You can also download the diamond model from here.
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· Add a poly plane and change its position to 0, 0; and width and height to 25 units.
· Add a new camera and position it so the diamond is focused at the centre.
· Add a spot light and position it.
· Change its attributes. Change the cone angle to 120 and penumbra angle to 10.
· Turn on Ray trace shadows and leave the default settings.
· Use area light under mental ray and change type to disc.
· Change the high samples to 4 into 4 and low samples to 1 into 1.
· Press control D to duplicate the light. Position it accordingly. Feel free to use your own position.
· Change the intensity to 0.75 and cone angle to 80.
Leave the rest as it is.
Do a render.
· Change the renderer to Mental Ray and render again.
· Change the quality to production.
· Sampling mode to custom.
· Min sample to 1 and max sample to 2.
· Turn on final gathering under indirect lighting tab and render. See the difference.
Add secondary lighting effect by selecting appropriate HDR map.
· Click on render settings. Click image based lighting and select the HDR map of your choice.
You can get free HDR maps by searching on Google.
Rotate the HDR sphere if needed.
Do a render. Depending on the hdr map you will get different lighting effect.
· Select the camera and add a lens shader under mental ray tab. Click on the lens shader tab and select mia exposure photographic shader.
Do a render. You will get nothing but black. Don't panic. We can adjust it.
· Change the film ISO to 200.
· Reduce crush blacks to 0.05.
· Finally cm2 factor value to 25000.
Do a render and save the scene.
It’s time to add shader to the diamond model. We will use mental ray material to make the diamond as real as possible.
· Select the diamond and Press shift + t to add a new material.
· Select mia material x under mental ray materials.
· Add a glass physical preset to the material.
Do a render. Now we will get a glass diamond.
Adjust the material property to make the diamond real.
· In the advanced reflection tab, turn off no highlights to visible area lights and skip reflection on inside.
· Change the index of refraction to 2.42.
· Under advanced refraction tab, turn off use max distance.
Render to see the result.
· Increase the max trace depth value to 20 for both advanced refraction and reflection.
· Also change the reflection and refraction values to 20 under quality tab in mental ray render settings. Remember to change the max trace depth value to 40.
Render to see the difference.
· Change the multi pixel filtering to Lancoz in order to make the render crisper.
Render again.
See the difference.
It’s time to add caustics.
· Enable caustics under indirect lighting tab in render settings. Change caustic photon type to cone.
You need to turn on photons and caustics in the lights also.
· Select the first spot light and turn on emit photons.
· Decrease the exponent to 1.
Do the same for the second light.
Render again to see the result.
See how caustics and shadows are behaving with the lighting.
You can increase the caustics effect by increasing the caustic scale value.
· Click on the white colour and increase the v value to 2.
Render again to see the difference.
Experiment with the values.
Due to the lack of dispersion shader we need to cheat the effect within the m i a shader itself.
Select the m i a material x and locate the refraction colour. We need to add custom texture to this slot in order to get the effect.
Add a ramp to the refraction colour.
Do a render to see the difference. You can see the caustics have the colour of the diamond.
We need to tweak the colour of the diamond to more clear white, which is like the actual diamond.
Go to UV texture editor and tweak the UV of the diamond as desired.
Change to face selection and select all the faces of the diamond.
Click on unitize option. This will scale the UV’s of all the faces to unity.
Then do layout. This will arrange the UV’s in a linear way.
Select the top flat faces and do a top planar projection.
Scale the UV and arrange it to the top left corner.
Change the top blue colour of the ramp to white and do a render.
You can notice the refractive caustics having the colour of the ramp. But the diamond has fewer colours.
Delete the red colour and move the green slot towards the white colour.
Check with the diamond model in the viewport. Fine tune if necessary.
Add a crater texture to the green colour slot.
Change the channel 1 and two to white.
Add a ramp to the channel 3 slot and change the colours to rainbow colours.
Do a render.
Scale the 3d texture of the crater while looking the colour change in the view port. Fine tune if necessary.
change the ramp to diagonal and do fine adjustments.
Adjust the shaker values as desired. Finally do a render.

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