[Python/OpenCV] Make Gaussian Shadow on Image

def generate_spot_light_mask(mask_size,
position=None,
max_brightness=255,
min_brightness=0,
mode="gaussian",
linear_decay_rate=None,
speedup=False):
"""
Generate decayed light mask generated by spot light given position, direction. Multiple spotlights are accepted.
Args:
mask_size: tuple of integers (w, h) defining generated mask size
position: list of tuple of integers (x, y) defining the center of spotlight light position,
which is the reference point during rotating
max_brightness: integer that max brightness in the mask
min_brightness: integer that min brightness in the mask
mode: the way that brightness decay from max to min: linear or gaussian
linear_decay_rate: only valid in linear_static mode. Suggested value is within [0.2, 2]
speedup: use `shrinkage then expansion` strategy to speed up vale calculation
Return:
light_mask: ndarray in float type consisting value from max_brightness to min_brightness. If in 'linear' mode
minimum value could be smaller than given min_brightness.
"""
if position is None:
position = [(random.randint(0, mask_size[0]), random.randint(0, mask_size[1]))]
if linear_decay_rate is None:
if mode == "linear_static":
linear_decay_rate = random.uniform(0.25, 1)
assert mode in ["linear", "gaussian"], \
"mode must be linear_dynamic, linear_static or gaussian"
mask = np.zeros(shape=(mask_size[1], mask_size[0]), dtype=np.float32)
if mode == "gaussian":
mu = np.sqrt(mask.shape[0]**2+mask.shape[1]**2)
dev = mu / 3.5
mask = _decay_value_radically_norm_in_matrix(mask_size, position, max_brightness, min_brightness, dev)
mask = np.asarray(mask, dtype=np.uint8)
# add median blur
# mask = cv2.medianBlur(mask, 5)
mask = 255 - mask
# cv2.imshow("mask", mask)
# cv2.waitKey(0)
return mask

def _decay_value_radically_norm_in_matrix(mask_size, centers, max_value, min_value, dev):
"""
_decay_value_radically_norm function in matrix format
"""
center_prob = norm.pdf(0, 0, dev)
x_value_rate = np.zeros((mask_size[1], mask_size[0]))
for center in centers:
coord_x = np.arange(mask_size[0])
coord_y = np.arange(mask_size[1])
xv, yv = np.meshgrid(coord_x, coord_y)
dist_x = xv - center[0]
dist_y = yv - center[1]
dist = np.sqrt(np.power(dist_x, 2) + np.power(dist_y, 2))
x_value_rate += norm.pdf(dist, 0, dev) / center_prob
mask = x_value_rate * (max_value - min_value) + min_value
mask[mask > 255] = 255
return mask

def _decay_value_radically_norm(x, centers, max_value, min_value, dev):
"""
Calculate point value decayed from center following Gaussian decay. If multiple centers are given, value
from each center sums up while limiting the accumulated value into [0, 255]
NOTE: assuming light at each center is identical: same brightness and same decay rate
"""
center_prob = norm.pdf(0, 0, dev)
x_value_rate = 0
for center in centers:
distance = np.sqrt((center[0]-x[0])**2 + (center[1]-x[1])**2)
x_value_rate += norm.pdf(distance, 0, dev) / center_prob
x_value = x_value_rate * (max_value - min_value) + min_value
x_value = 255 if x_value > 255 else x_value
return x_value

def add_gaussian_shadow(frame, light_position=None, max_brightness=255, min_brightness=0,
mode='gaussian', linear_decay_rate=None, transparency=None):
"""
Add mask generated from spot light to given image
"""
if transparency is None:
transparency = random.uniform(0.1, 0.5)

height, width, _ = frame.shape
# hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
yuv = cv2.cvtColor(frame, cv2.COLOR_BGR2YUV)
mask = generate_spot_light_mask(mask_size=(width, height),
position=light_position,
max_brightness=max_brightness,
min_brightness=min_brightness,
mode=mode,
linear_decay_rate=linear_decay_rate)


# hsv[:, :, 2] = hsv[:, :, 2] * transparency + mask * (1 - transparency)
# frame = cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR)
yuv[:, :, 0] = yuv[:, :, 0] * transparency + (mask.astype('float') * yuv[:, :, 0] / 255.0) * (1 - transparency)
frame = cv2.cvtColor(yuv, cv2.COLOR_YUV2BGR)
frame[frame > 255] = 255
frame = np.asarray(frame, dtype=np.uint8)
return frame

 

 

* Original Codes : medium.com/@fanzongshaoxing/adjust-local-brightness-for-image-augmentation-8111c001059b