[Steve Brown]

Hi Craig, try this. It will sample the Lightning layer, using the current position of the layer that you apply the sliders (and the expressions) to:

//red slider
target = thisComp.layer("Lightning Layer");
colorValue = target.sampleImage(transform.position, radius = [.5, .5] );
outputValue = (colorValue * 255);
outputValue[0];

//green slider
target = thisComp.layer("Lightning Layer");
colorValue = target.sampleImage(transform.position, radius = [.5, .5] );
outputValue = (colorValue * 255);
outputValue[1];

//blue slider
target = thisComp.layer("Lightning Layer");
colorValue = target.sampleImage(transform.position, radius = [.5, .5] );
outputValue = (colorValue * 255);
outputValue[2];

//alpha slider
target = thisComp.layer("Lightning Layer");
colorValue = target.sampleImage(transform.position, radius = [.5, .5] );
outputValue = (colorValue * 255);
outputValue[3];

[Steve Brown]

ToonIt is a filter, it will automatically generate the lines between regions of high contrast.

“Write On” is the effect you’ll probably want to use to reveal the drawing, look for a tutorial on that.

[Steve Brown]

You probably won’t be able to preview the whole thing in real time, though you can certainly do so in sections, by setting your work area to the portion you wish to preview and using the RAM preview option (keypad 0)

You also might want to try zooming out to 25% or 50% and setting the veiwer resolution accordingly.