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Tone Mapping refers to the technique of adjusting the colors of a rendered image in the camera in order to bring them within a value range that looks a bit better on a computer screen. This is used most often when you're using techniques such as image-based lighting, or IBL nodes, or the Physical Sun and Sky shaders, and is also used when you're using materials such as the MIA materials: Mental Images Architectural materials. These are physically accurate, and meant to simulate the properties of materials in the real world.
Sometimes rendering with them can cause them to look blown out, or add too much contrast in the renders. This is a situation when you might want to do Tone Mapping, and I will show you some very simple ways to get started with Tone Mapping in Maya. In this particular scene, I have my little Frankenstein monster toy and a couple of spheres just to see how the image-based lighting is working. And I have an image-based lighting node right here. And I'm using the sky2.hdr image. This is located in the Source Images directory of the current project, and this is a simple directionalLight with Raytrace Shadows to create the effect of direct lighting.
So I will do a quick render here. So we can see in this particular render, the HDR we are using for the image-based lighting is causing a little bit of over-bright qualities to this highlight here, as well as some of the colors are overly saturated, and there's quite a bit of contrast in here. It's a little bit hard to see what's going on. So I am going to store this image and go to my renderCam camera, and in the renderCamShape tab of the Attribute Editor I am just scrolling down here to mental ray, and I will click the checker box next to Lens Shader to open up the Create Render Node window.
Under the mental ray section, I will click on Lenses, and I am just going to use the mia_exposure_simple node to do my Tone Mapping. The other one you can use is the exposure_photographic node. This has more controls that are related to real-world cameras. I will keep things simple just by using this one. By clicking in that, it connects it to the camera, and the Attribute Editor opens up to the mia_exposure_simple tab. So I will do another quick render just to compare the results using the default settings here.
So in this render, we can see that we've lost a fair amount of contrast. Overall the image has been brightened. This is what we had before. So the default settings are causing this to be much brighter, but we can adjust that using the settings here. So I will store this image. The first thing I'm going to do to bring some of the contrast back is I am going to set the Pedestal to a negative value, but a very, very small one. I found for this particular image, I am going to do -0.02. By setting this to a negative value, it's kind of like if you had an image in Photoshop and you are going to adjusting the levels, and you wanted to as I say, crunch the blacks, in other words, bring the black levels up to add more contrast to the scene.
That's what the Pedestal setting is doing. The Gain is adjusting the overall brightness. It's kind of like a brightness knob for the scene. But before I get to that, let's render a small section here and see how adjusting the Pedestal has worked. If I move the Pedestal in a positive direction, it's going to add the light grayness to the shadows. It's going to remove even more contrast from the image. So I am going in a negative direction right now, just very slightly.
So if I store this and compare, it's starting to get more contrast in the image. So I am going to lower the Gain to bring some of that brightness down under control. Bring this down to 0.5. You can see how this is progressing. So there is our original render. This is adding and adjusting. So it's really a matter of balance, playing with these settings until we get something that looks good on the computer monitor. The Knee value is good for fine-tuning, and generally speaking a value between 0.5 and 0.75 is pretty good.
This is sort of like an adjustment curve to the overall values. The last thing I am going to adjust is the Gamma. I am just going to bring this down a bit, which will also have to bring down the overall brightness of the scene. I bring this down to 2. This should, of course, be adjusted based on your computer monitor's Gamma settings. So here's the image after I've made adjustments. So that's the original render, and here is what I have now. So it's basically a way to adjust the color values in the rendered image while you're working on it, and it's the easiest way to go about tone mapping is to add the mia_exposure_simple Lens Shader to the Lens Shader of the rendering camera.
What I would like to show you also is when you create something like the Physical Sun and Sky network, it actually automatically adds a Lens Shader to all the rendering cameras in the scene. This essentially does the same thing. It's there for automatically Tone Mapping. It's not created when you are using image-based lighting, but it is when you create Physical Sun and Sky. So if I hide these image-based lighting and the directionalLight and if I go into Render Settings, what I will do is I will take my renderCam, I am going to Break the Connection here to remove this Lens Shader, but I will show you, if I, if I go to Physical Sun and Sky and press Create, and now I select my renderCam camera, it's created a second mia_exposure_simple2 node.
And this actually has some default settings placed in there to adjust the image. So if I render it now, this is what I get for this. So this is what I get just from adding the Physical Sun and Sky network to the scene. You can see if I select the renderCam camera and break the connection again so that I have no Lens Shader on here and then just simply render, I am just going to render a region here, but you will see things will look very off.
In this case, the Physical Sun and Sky shader has made things very, very bright. So Tone Mapping is there for you to adjust the values of the image whenever you're using some kind of physical lighting simulation.
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