Hello @debapriya,
You are asking for help without providing relevant details. Just saying I’ver performed registration and “the transformed ROI image is an all black image.” is not a useful description of the problem.
There could be issues with:
- Registration failing (converging to a local minimum that is far from the one that aligns the images).
- Resampling (using the wrong transformation direction or grid definition).
- Visualization (which you already encountered in your other question).
You need to confirm success of each sub-step before you can move on to the next step.
Having said this, I will hazard a guess at the issue just based on the images:
The ROI image looks like a contour and not the object itself. When the ROI signal is sparse, high frequency, you will often encounter aliasing when performing resampling. See this question and guidance on how to resolve this specific issue.
If this does not address the problem, you will need to provide a more complete description.