Flicker of 2ch image on CompositeImage.updateAndDraw


I am reconstructing my plugin which can create 2ch image from 1ch image of 2 ROIs.
And it has a preview window as color or composite image.
The preview window repaint the image while these ROIs are moving.
In color mode is no problem.
However, there is a problem with redrawing of the second channel image in composite mode
All case of repainting image, second image is flickered.
It probably seems to be a problem with the updateAndDraw and updateChannelAndDraw method.
Furthermore, it may be the problem of the ImageWindow or higher.

Could anyone give me some advice to solve it?

short sample code

CompositeImage viewImage; // this image is preview image.

//**multithread, Change every time at ROI moving**//
CompositeImage newImage; //this image is 2 stacks image as 2ch.