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In Nuke, once you've read in your nodes and set up the merges, you can start to change the operation. I'll double click on merge one, to make sure that it shows up at the top of my properties tab. And, up at the top we can see the operation is set to over. I've also got merge 2 selected and showing in the view. You can switch around what you're viewing by, picking that node for example merge 1 and pressing, 1. There's that ambient occlusion, over the beauty. I'll change this operation from over, to multiply and now we can see the occlusion, multiplying over that beauty pass.
Remember in multiply, we're multiplying the over color by the under color in the red, green, and blue channels, and dividing by the color space. For example, if you're working in an 8 bit image or 256 possible values of red let's say, we're multiplying the over value of the red times the undervalue of the red, and dividing by, 256, that color space. The result is always darker and multiply. And multiplying by white, is like multiplying by 1, there's no net effect. So, in this case, with my ambient inclusion being mostly white, just the dark shows through and the white areas leave the under image alone.
Now, with merge 1 in, I can look at merge 2. I'll double click on it, press 1 to show it in the viewer, and set the operational for the screen. Typically, if you're running a lighting pass like this, such as a specular highlight or par T volume, you can screen it over. You can also use plus or add if needed, but that does blow out to white really quickly. There is another issue here. And I'll take care of it before I go any further. We can see in this, by selecting that par T volume, and pressing 1, that it was run at 640 by 360.
It's a half size render. In this original merge then, when the merge is set to, over, we can see there's an issue. We're getting some streaking there, because this image is simply repeating the last color. What I'll do then, is insert a re-format note before that merge, selecting the party volume, right clicking, choosing, Transform and, Reformat. Reformat, as the name suggests, allows you to reformat an image to a distinct size. I'll drop down here under output format, and choose, 1280 by 720.
Alternately, you can put out to a box, such as a bounding box or a scale. Now, that, that's reformatted to 1280 by 720, it's going to fit over correctly, and we'll get rid of the streaking. I'll make sure I go forward and press, 1 to show merge 2, double click on merge 2 to make sure that it shows in the properties tab, and set the operation from over, to screen. Now I've got my par t volume showing, and it's a soft, gauzy haze over the right side of the image. In my view then, I can click here and press, F to fit and Nuke will fit, that image as big as it can in an even magnification.
Alternately, if we drag down the timeline just a little bit, to make a little more space, we can click in the viewer and press, H to fill. The difference here is that, F for fit, fits at an even multiple, or at least a whole number. H then, goes at an odd size. When I was pressing F, I was getting a 1 3rd size image. Right now though, pressing H gives me, well divided by 2 and one half. So, it's an odd size and may introduce some, visual aliasing artifacts, which are not actually part of the image.
But, simply a result of the magnification. What you need to do is decide if you need to see, the overall colors, or to be able to focus on fine detail, and zoom in accordingly. Now, that I've got the blending mode set, I can start to look at, mix or opacity for each merge. Every merge in Nuke has its own mix amount, as do most of the other nodes, that involve an A over B. They allow you to, back off how much of that you're seeing. For example, I'll double click on Merge 1 and, back off the mix.
With my ambient occlusion at 0% in the mix, there is no occlusion there. And I can really see I am, missing the detail on some of the doors. As I pull it all the way forward to 1, we can really see that darkness showing up, and all the joints and reveals, and the little steps in the geometry. I'll back this off to about .75. So, it adds some grounding darkness without, overly darkening areas I have worked hard to light. For merge 2 then, I'll back off that mix as well, pulling it down to about 0.75 or so. So, I get a little bit of that lighting that par t volume showing, without it totalling blowing out the white wall.
You can always come back and adjust this later, but, it's a good idea to. Put it in full strength, because you have the range, and use that mix to adjust where that sits, so you get the right, look as the, different read notes are merging together.
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