Is there a WYSIWYG tool for a SmoothCurve?

[silverwing]

Hi, All!
There is such an avisynth-plugin for adjusting YUV color space - SmoothCurve,
part of SmoothAdjust plug-in written by LaTo.
I tried using the YUV Curve tool (Edius, see screenshot),
I set the control points, then I transfer them in the form of coordinates in SmoothCurve.
But this is not very convenient, because YUV Curve by Edius does not allow fine-tuning
to correct the spoiled color (for example, the daytime sky has a purple hue,
but not grayish or bluish) - too small a scale for adjusting Y, U, V channels.
Is there a convenient WYSIWYG tool for SmoothCurve in nature?
Thank you for attention.
(Sorry for my bad English)