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Lighting and Rendering with mental ray in Maya with Eric Keller shows how to master practical mental ray techniques for rendering models created in Maya. This course walks through the most efficient and innovative mental ray techniques, including direct versus indirect lighting methods, creating different types of shadows, using the new ShadowMap camera, and reusing shadow and final gathering maps. A chapter on optimizing render times and enhancing render quality is also included. Exercise files are included with the course.
You can use Maya's render layers to separate the objects, lighting, and textures of a scene for easy compositing in other programs, such as Photoshop or Adobe After Effects. I have a simple scene here with dining room has very basic textures applied. I want to demonstrate how I've separated this room into render layers. So, the Render Layer Editor is located beneath the Channel Box. If I have the Channel Box closed, I'll just click on this tab to open it up again. You'll see the Layer Editor here at the bottom. I'm going to switch over to Render, and this is where you'll find the render layers.
There's a defaultRenderlayer, and then I've also created three custom render layers: itRoom_RL, volumeLight_RL, and channelMasks_RL. The litRoom has the basic objects in the scene, and the lighting, and these have been textured. The volumeLight is a special layer that I've created that just has volumetric lighting effects. If I turn on Wireframe on Shaded, you can see that the geometry is actually in the scene. And then I have a channelMasks layer that basically has red, green and blue shaders applied to specific objects in the scene so it'll be easier to composite in Adobe Photoshop or After Effects.
So, I'm going to click on this render layer and just do a quick render, so we can what it looks like - quick being extremely relative. Okay, now that that's rendered, I'm going to store this image, minimize the Render view, and I'm going to select in the volumeLight render layer and do a quick render from here. So, I'm going to store that image as well. So, now I have this one, and I also have this one.
And then finally, I'm going to click on the channelMasks render layer and render this one. Let's double-check to make sure that I've stored this image. Now, let's do render from renderCam. And there we go. Just to show you why these are useful, I'll save each one to the desktop as a TIFF. So, I'll call this roomChannelMask.
Save this one as a TIFF as well, on my desktop. I'll call this roomVolumeLight. I'll save this one to the desktop as well, and I'll call this roomLit. Save my scene, and open up Adobe Photoshop. So, I have each of the images that I created using render layers opened in Photoshop, and I just want to give you an example of why using render layers can make your life much easier when compositing.
So, here I have the textured and lit room, I also have my volumetric lighting, and I have my channel masks So, what I'm going to do is I'm going to first go to my volumeLight I'm going to do Select All, Edit > Copy, go back to roomLit and just paste this in here, and it's going to appear as a separate layer. So, I'm going to take this layer, and I'll just set it to screen. So, now you can see the light on top of the rest of the room. Rendering volumetric effects like this in Maya using mental ray is very expensive.
It takes a long time to render. By separating this using render layers, it makes my life easier because if I need to change the way this light looks, all I need to re-render is the volumetric lighting layer. I don't need to re-render the entire scene. So that saves me a lot of trouble. And plus, now that I have this separated in Photoshop, I can make adjustments here to the composit without having to re-render anything. So, for instance, I can go in here. If I want to make it brighter, I'll adjust the levels, bring this up a little bit.
I can add a little bit of blurring, maybe a little bit of Gaussian Blur. Let's make it a bit softer. And using the channels mask, I'm going to select this image, copy it, and paste it as a separate layer. Now, I'm going to use this as a way to select the different elements of the scene. I've applied just the green shader to the glass globes around the chandelier, and I've applied the blue shader to the lampshades and the candle flames.
So by opening my Channels editor here, just by going to Windows > Channels, I can select the Red layer, which is just the geometry of the scene. I'm going to Ctrl+click on this to select just what shown in red here, just the geometry. I'm going to hide layer and go back to my Background layer. And now you can see I have all the geometry of the scene selected. So, if I wanted to make some kind of adjustment to that, for instance, let's say the color, maybe I want to pump up the Saturation, make it slightly warmer colors, I can do that.
I can go back to this layer, I'll deselect everything, and I'll switch to the Green channel and Ctrl+click here. So, now I have just the globes of the chandelier selected. I'll go back to the Background here, disable this, and again, I can make adjustments to just the globes. So, for instance, if I wanted to add some color to them, I can turn on Colorize, maybe lower the Lightness a bit, increase the Saturation, and so on and so forth.
I need to turn that layer on. So, here I am in this layer. I can go over to the Blue channel and Ctrl+click here, and now I just have the lampshades and the candle flames selected. I can continue to make changes as I need to, without having to re-render. So, this is one of the reasons why render layers are so useful when rendering in Maya.
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