The Levels node in Conduit is basically equivalent to the Levels adjustment in Photoshop, so it’s easy to think of it as an image operation foremost. Yet Levels actually performs a very general-purpose math operation that can come in handy in many situations.
Consider an effect that takes a value from the user using the Slider node. The slider’s value is usually in the range 0 to 1 (what is often called the “standard range” in Conduit because it’s the range for visible pixel values). What if we want this slider to drive a value that needs a larger range — for example, a 2D Transform node? If we want to use this slider to move the image up to 100 pixels in either direction, we’ll need to change the slider’s input value’s range from [0, 1] to [-100, 100].
This could of course be accomplished by using a few basic math nodes:
But that looks rather unweildy for such a simple operation… So let’s use Levels instead:
See what happens in Levels? Input black and input white specify the original range (in this case, 0 to 1). Output black and output white specify the output range. This performs exactly the same math as the Multiply+Subtract nodes in the first screenshot.
Don’t forget that the Clip to 0-1 setting is enabled by default when a Levels node is created, so you need to uncheck that box. (If you don’t, Levels will clip all negative values to zero and all >1 values to one.)
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