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So in addition to everything else that we can do within image, another thing we can do is convert the values of a pixel or the entire image or portions of the image from one value to another value. And these are all in the Converter family of nodes. To start, let's go ahead and click the Render button and here we have Suzanne in front of a textured cube. First up is the ColorRamp node. Now every pixel in this image has a value.
So and if we drag over we can see what those color values are and they range anywhere from almost one pure white to pure black to every color in between. The ColorRamp node then maps each value that comes in to a different color. So it ramps these colors smoothly from one color to another. In this case, I've set up 1, 2, 3, 4, 5 colors. So at the far left, we have black and then we go to a medium gray and then we go up to a green color, to a blue color, and then finally to a white color.
So what I've done is recolor this entire image based on this ColorRamp. I can also convert this image to a black-and-white image by clicking on the Input node, in this case the Render Layer node, coming down to Converter, RGB to BW. And then since it puts out a value really because it's just converting that to the black-and-white scaled image values of each pixel, which is the numbers that are then effectively fed to the factor input of the ColorRamp to recolor that image.
The ID Mask is a very cool node, and what we've done over here in 3D view, I'm going to right-click on Suzanne and for Mac users you want to Command-click. What we have over in the Object panels is what's called a Pass Index, and by setting this number to a certain value, we can uniquely identify each different object in Post-Pro. So the cube is Pass Index of 1, and Suzanne is the Pass Index of 0.
So what this ID Mask node does and you have to enable Index Objects as a render pass to get the socket to show up. What this does then is it gives us a mask of where the pixels from the cube are showing. And so now I can pull the mask for just the cube, and say I wanted to convert that to a different color, I could then feed this as an Alpha value to the Factor value. And then that way just change the colors, or in this case assign a flat color to the cube, as you can see.
So use this to pull the mask, most often times you want to pull the mask and then either maybe apply a filter to that object, or soften it, or sharpen it up, or like we've done here, changed the colors up and you can even then blend this color and with the original color, and then ultimately recolor just one of the objects in the image. The last set of nodes is where you separate out and you can work on the individual color channels. So I'd like to come up here to Scene and YCbCr because we're going to work with the high-def channels of the image like that.
And we're going to go ahead and pull in the render layer and thread that to the separate YCbCr, which stands for Luminance, Chrominance, and we're going to go ahead and pull in the image from Converter, which is the image of Suzanne because she is just a little more interesting. So what we have here is a separate node that breaks this image from the composite, if you will, of all of the different color channels into Y, which is Luminance, Cb, which is your Chrominance in the blue direction, and Cr, which is the Chrominance in the red direction, along with the Alpha Channel.
And what I usually do is I've broken these out and run them through ColorRamp nodes and then ultimately after you do your adjustment you can then feed them back to a combined node and combine these channels back into the final composite output. I am going to go ahead and Shift+D to duplicate the Viewer node and crank it in over here. So we've taken this image. We haven't touched the Chrominance in either direction, but what we have done is we have taken the Y value, the Luminance and remapped it using the ColorRamp node.
So instead of going from a normal 0 to a normal 1, now the middle gray values will have a full Luminance. So what we've done is in fact, we've made the overall picture that much brighter. We've also played a little game down here. And we're going to take that Luminance Channel and use it as the Alpha value. So now we have an image that has Alpha values based on the brightness of the overall image. And so effectively you could make dark areas of the image where it has a very low Luminance to be Alpha zero and very bright areas of the image to be fully opaque.
Each of the pairs of separate, combined images work exactly the same. It's just that there are different ways to break out the channels. So you have your red, green, and blue, your Hue/Saturation and Value, your YUV, which is the European Broadcast Standard for Luminance and then the U and V are colors. And then the CbCr, which is your high- definition, and the new way of looking at a spectrum of colors and being able to effectively transmit these colors over the bandwidth.
So, that is the Converter nodes and the ways in which you can convert the pixel values or color values from one value to another and shift your Color Spectrum of your image.
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