How can i define regions of a color image?

Hello I'm using multiresolution (with 3 stages) based wavelet transform and watershed algorithm for image segmentation. In order to merge the regions, i used inverse wavelet transform after the watershed algorithm (from stage 3 to stage 2) and obtained an image at stage 2. Then i applied watershed for my image at stage 2 (after the direct wavelet transform). So i obtained two copies of the image : the first is after a watershed segmentation (at stage 3) followed by region projection using inverse wavelet transform. The second is after a direct wavelet transform followed by watershed segmentation at stage 2. I want to compare the two obtained images in order to merge the over-segmented regions: I determined the centroid of each region of the second image. I want to find the coordinates of these centroids in the first image, extract the labels associated to them, and replace them in the second image in order to obtain a merged image. The problem is i don't get how to define the regions of the first image and the labels associated to them (because i applied inverse wavelet transform after watershed segmentation). Does anyone have any suggestions please? Thank you so much for your help