How can an image be rotated with OpenCV with a custom colour for the gaps around the edge?

Question

I would like to rotate an image in OpenCV (I'm currently doing it this way image manipulation SO answer ) but would like to specify the colour used to fill the gaps created by the rotation - by default, it's black (see below)

How could this be done?

Answer 1

I think the answer lies in the official doc :

C: void cvWarpAffine(const CvArr* src, CvArr* dst, const CvMat* map_matrix, int flags=CV_INTER_LINEAR+CV_WARP_FILL_OUTLIERS, CvScalar fillval=cvScalarAll(0) )

where

CvScalar fillval=cvScalarAll(0) specifies the fill color of the "gap".

Just specify the fillval with a color scalar when calling this function.