Set background of Python OpenCV warpPerspective -


when using warpperspective scale image smaller, there black area around it. may like:

or

how make black borders white?

pts1 = np.float32([[minx,miny],[maxx,miny],[minx,maxy],[maxx,maxy]]) pts2 = np.float32([[minx + 20, miny + 20,                    [maxx - 20, miny - 20],                    [minx - 20, maxy + 20],                    [maxx + 20, maxy + 20]])  m = cv2.getperspectivetransform(pts1,pts2) dst = cv2.warpperspective(dst, m, (width, height))

how remove black borders after warpperspective?

if @ documentation warpperspective function online opencv documentation (http://docs.opencv.org/modules/imgproc/doc/geometric_transformations.html) says there parameter can give function specify constant border color: 

cv2.warpperspective(src, m, dsize[, dst[, flags[, bordermode[, bordervalue]]]])

where 

src – input image. dst – output image has size dsize , same type src . m – 3\times 3 transformation matrix. dsize – size of output image. flags – combination of interpolation methods (inter_linear or inter_nearest) , optional flag warp_inverse_map, sets m inverse transformation ( \texttt{dst}\rightarrow\texttt{src} ). bordermode – pixel extrapolation method (border_constant or border_replicate). bordervalue – value used in case of constant border; default, equals 0.

so like: 

cv2.warpperspective(dist, m, (width, height), cv2.inter_linear, cv2.border_constant, 255)

should change border constant white color.


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