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# Nuke 101: Color Correction

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## Creating Curves with ColorLookup

The ColorLookup node mentioned at the beginning of this lesson is actually an I/O graph you can control directly. This makes it the operation with the most amount of control. However, it's actually the hardest to control and keyframe due to its more complicated user interface. After all, it's easier to set a slider and keyframe it than move points on a graph.

Let's try this node on both the image and the I/O graph itself.

1. Replace RolloffContrast2 with a ColorLookup node in the Color toolbox (FIGURE 4.18).

The interface for this node has the narrow curves list on the left, and the curve area on the right. Choosing a curve at left displays that curve at right, which enables you to manipulate it. There are five curves. The first controls all the channels, and the next four control the R, G, B, and alpha separately. You can have more than one curve display in the graph window on the right by Shift-clicking or Ctrl/Cmd-clicking them in the list.

2. Click the Master curve in the list at left.

In the graph (Figure 4.18), you can now see a curve (a linear one at the moment). It has two points that define it, one at the bottom left and one at the top right. Moving them will change the color. For example, moving the top one will create a Multiply operation.

The ColorLookup's strength lies in making curves that you can't create using regular math functions. For that you need to create more points.

3. To create more points on the curve, Ctrl/Cmd-Alt/Option-click the curve in the graph window. It doesn't matter where on the curve you click.

You've just created another point. You can move it around and play with its handles. If you look at the I/O graph on the Viewer, you can see that it mimics what you did in the ColorLookup node. They are exactly the same (FIGURE 4.19).

Now let's use ColorLookup on the car image.

4. Select Read1 and Shift-click the ColorLookup node in the Color toolbox to branch another output.
5. Click ColorLookup2 and press the 1 key to view it in the Viewer.
6. Play around with ColorLookup2's curves. You can play with the separate RGB curves as well.

I ended up with FIGURE 4.20—pretty drastic. But that's the level of control you have with ColorLookup. The Reset button at bottom left allows me to reset this mess.