opencv cv2.copyMakeBorder padding

opencv:https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_core/py_basic_ops/py_basic_ops.html

Making Borders for Images (Padding) If you want to create a border around the image, something like a photo frame, you can use cv2.copyMakeBorder() function. But it has more applications for convolution operation, zero padding etc. This function takes following arguments:

src - input image top, bottom, left, right - border width in number of pixels in corresponding directions borderType - Flag defining what kind of border to be added. It can be following types: cv2.BORDER_CONSTANT - Adds a constant colored border. The value should be given as next argument. cv2.BORDER_REFLECT - Border will be mirror reflection of the border elements, like this : fedcba|abcdefgh|hgfedcb cv2.BORDER_REFLECT_101 or cv2.BORDER_DEFAULT - Same as above, but with a slight change, like this : gfedcb|abcdefgh|gfedcba cv2.BORDER_REPLICATE - Last element is replicated throughout, like this: aaaaaa|abcdefgh|hhhhhhh cv2.BORDER_WRAP - Can’t explain, it will look like this : cdefgh|abcdefgh|abcdefg value - Color of border if border type is cv2.BORDER_CONSTANT

src ： 输入的图片 top, bottom, left, right ：相应方向上的边框宽度 borderType：定义要添加边框的类型，它可以是以下的一种： cv2.BORDER_CONSTANT：添加的边界框像素值为常数（需要额外再给定一个参数） cv2.BORDER_REFLECT：添加的边框像素将是边界元素的镜面反射，类似于gfedcb|abcdefgh|gfedcba cv2.BORDER_REFLECT_101 or cv2.BORDER_DEFAULT：和上面类似，但是有一些细微的不同，类似于gfedcb|abcdefgh|gfedcba cv2.BORDER_REPLICATE：使用最边界的像素值代替，类似于aaaaaa|abcdefgh|hhhhhhh cv2.BORDER_WRAP：不知道怎么解释，直接看吧，cdefgh|abcdefgh|abcdefg value：如果borderType为cv2.BORDER_CONSTANT时需要填充的常数值。

img = cv2.imread('testimg.png')
img = cv2.resize(img,(256,256))
cv2.imshow('origin',img),cv2.waitKey(0),cv2.destroyAllWindows()

replicate = cv2.copyMakeBorder(img,20,20,20,20,cv2.BORDER_REPLICATE)
cv2.imshow('replicate',replicate),cv2.waitKey(0),cv2.destroyAllWindows()

constant = cv2.copyMakeBorder(img,20,20,20,20,cv2.BORDER_CONSTANT,value=(255,255,255))
cv2.imshow('constant',constant),cv2.waitKey(0),cv2.destroyAllWindows()

reflect = cv2.copyMakeBorder(img,20,20,20,20,cv2.BORDER_REFLECT)
cv2.imshow('reflect',reflect),cv2.waitKey(0),cv2.destroyAllWindows()

reflect101 = cv2.copyMakeBorder(img,20,20,20,20,cv2.BORDER_REFLECT_101)
cv2.imshow('reflect101',reflect101),cv2.waitKey(0),cv2.destroyAllWindows()

wrap = cv2.copyMakeBorder(img,20,20,20,20,cv2.BORDER_WRAP)
cv2.imshow('wrap',wrap),cv2.waitKey(0),cv2.destroyAllWindows()