OpenCV中的梯度方向

通过Sobel算子,我可以确定图像的梯度大小。我在下面显示:

现在我想确定梯度方向。为此,我正在跟踪 this post,它利用了函数 cv2.phase . 然后,根据函数返回的度数,将角度硬编码为特定颜色。我的问题是这个函数为我返回的值在0到90度之间。因此,我得到的图像只有红色和青色。

我的代码如下:

# where gray_blur is a grayscale image of dimension 512 by 512

# 3x3 sobel filters for edge detection
sobel_x = np.array([[ -1, 0, 1], 
                   [ -2, 0, 2], 
                   [ -1, 0, 1]])


sobel_y = np.array([[ -1, -2, -1], 
                   [ 0, 0, 0], 
                   [ 1, 2, 1]])


# Filter the blurred grayscale images using filter2D

filtered_blurred_x = cv2.filter2D(gray_blur, -1, sobel_x)  
filtered_blurred_y = cv2.filter2D(gray_blur, -1, sobel_y)

# Compute the orientation of the image
orien = cv2.phase(np.array(filtered_blurred_x, np.float32), np.array(filtered_blurred_y, dtype=np.float32), angleInDegrees=True)

image_map = np.zeros((orien.shape[0], orien.shape[1], 3), dtype=np.int16)

# Define RGB colours
red = np.array([255, 0, 0])
cyan = np.array([0, 255, 255])
green = np.array([0, 255, 0])
yellow = np.array([255, 255, 0])

# Set colours corresponding to angles
for i in range(0, image_map.shape[0]):
    for j in range(0, image_map.shape[1]):
        if orien[i][j] < 90.0:
            image_map[i, j, :] = red
        elif orien[i][j] >= 90.0 and orien[i][j] < 180.0:
            image_map[i, j, :] = cyan
        elif orien[i][j] >= 180.0 and orien[i][j] < 270.0:
            image_map[i, j, :] = green
        elif orien[i][j] >= 270.0 and orien[i][j] < 360.0:
            image_map[i, j, :] = yellow

# Display gradient orientation
f, ax1 = plt.subplots(1, 1, figsize=(20,10))

ax1.set_title('gradient orientation')
ax1.imshow(image_map)

显示图像:

提前谢谢。