OpenCv unable to extract Features from images that are scaled in Java

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Hi, I am using OpenCV & Java to compare same images based on feature. I observed whenever I resize either of the two images using java, the descriptor1.cols() = 0, thereby all the comparisons failed. In case, I do not want to resize the image I need to set the tolerance level (mat point distance) at around 70 - 80. I am using the same code from below web site, and it does work correctly when both images are of similar sizes and mat point distances are below 15.

http://xmlmanager.blogspot.in/2015/09...

Can you suggest, why OpenCv is not able to gather the features, when the image was resized using Java?