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In this video we're going to cover the two kinds of Transparency that are handled in Blender. So what I would like you to do first is switch over to the transparency scene by clicking on Transparence, and if you press F12 to do the Render or Mac users through the Scene Render button, you should get this image of Susanne inside this semi-transparent globe. There's a couple of things to point out here. Number one, let's look at the globe. The globe has an Alpha value of 0.3.
You'll recall that 1 is fully opaque and 0 is completely transparent. So at 0.3 we can sort of see the globe and it's shaded gray, with a red specular color. So as the light hits the glass, even though it's colored gray, it picks up some red coloring as the light travels through the glass and comes back out to see us. The main Ray Transparency settings are down here under the Mirror Transparency panel, and we have a couple of controls that I'd like to go over. One is the Index Refraction. That's the amount of bending of the light and the Fresnel Effect is kind of a magnifying effect that happens when light passes through bent glass.
So, let's go ahead and crank those up, and now if we press F12 again. Now, under Render you can see that the image has been bent by passing through the glass, reflecting off Susanne, and then passing back out through this rounded lens, so the glass is acting sort of as a lens, and we can simulate that in Blender. Glossiness is the fact that no glass or anything that light passes through is perfectly transparent. So as we crank down the Glossiness a little bit, we can barely make out the outline of Susanne through the glass.
We want to crank up the value, notice we've got some speckling going on here, and that's because not enough samples are being taken. So if we do crank down the Glossiness we want to increase the number of samples. It's going to take longer but it's going to give you a higher quality result. Now, when light passes through glass and then passes through another piece of glass and then comes back out again, there's a lot of refraction going on, and just like with mirrors there's a lot of calculations that need to happen. So this control allows you to set the number of refractions that are going to be computed and I find that 2 is plenty.
As light passes through something, some of it's absorbed and then other parts of it is reflected back out. And you can control the absorption here, as well as reduce the specularity on transparent materials as the light passes through, so you get less of this red bloom. Now Ray Transparency is very physically accurate. As you can see, we can simulate any kind of material. There's readily available tables for the Index, or Refraction, for any kind of material like glass, or water, or diamonds, or quartz, anything like that.
The other kind of Transparency is called ZTransparency, and that's right up here under Z. And if we have the globe selected and press Ztransparency, notice that Ray Transparency comes off. ZTransparency is very fast to compute as you've seen here, but it's not physically accurate at all. There is no real control over the bending of light as it passes through the objects. However, it is very fast. The last thing when dealing with Transparency is when you're rendering a transparency. Even though this card here is colored gray with a red specularity, it's blue in the image.
And the blue that it's picking up is from the World settings, namely the Horizon blended up to the Zenith. So that's not too good because that blue color may carry over in any subsequent rendering. So what we would want to do is come to the Scene Render Settings and click Premultiply. Now when we render, when we drag over the background area here, you can see in the Image Editor the RGBA values, expressed as both an 8-bit value and a number between 0 and 1, along with the Z value, distance from the camera for every pixel in the image.
And here we can see that the background has a value of 0.2 Alpha, as well as, kind of a gray color. We can now then composite this over another background matte image and some of the matte colors will come through and it'll be looking like we're through kind of a dark glass or smoky colored window. So those are the two approaches to handling Transparency in Blender.
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