def invert(img, mx=None):
"""
INVERT applies inverse video transformation on single channel images.
Usage:
res = invert(img, max_intensity)
Args:
img (numpy.ndarray): single channel image
max_intensity (implicit none): the maximum intensity of the type of
images provided as input (e.g. a 8 bit/pixel image has normally
max_intensity=255)
Returns:
numpy.ndarray: an image of the same shape as the original, but with
the intensity levels inverted (max_intensity - initial_value)
Raises:
ValueError: if the input image is not single channel
"""
if img.ndim != 2:
raise ValueError('A single channel image is expected')
if mx is None:
mx = dtype_limits(img)[1]
else:
mx = np.min(dtype_limits(img)[1], mx)
res = mx - img
return res
def invert(img, mx=None):
"""
INVERT applies inverse video transformation on single channel images.
Usage:
res = invert(img, max_intensity)
Args:
img (numpy.ndarray): single channel image
max_intensity (implicit none): the maximum intensity of the type of
images provided as input (e.g. a 8 bit/pixel image has normally
max_intensity=255)
Returns:
numpy.ndarray: an image of the same shape as the original, but with
the intensity levels inverted (max_intensity - initial_value)
Raises:
ValueError: if the input image is not single channel
"""
if img.ndim != 2:
raise ValueError('A single channel image is expected')
if mx is None:
mx = dtype_limits(img)[1]
else:
mx = np.min(dtype_limits(img)[1], mx)
res = mx - img
return res
def threshold_sauvola(image, window_size=15, k=0.2, r=None):
"""Applies Sauvola local threshold to an array. Sauvola is a
modification of Niblack technique.
In the original method a threshold T is calculated for every pixel
in the image using the following formula:
T = m(x,y) * (1 + k * ((s(x,y) / R) - 1))
where m(x,y) and s(x,y) are the mean and standard deviation of
pixel (x,y) neighborhood defined by a rectangular window with size w
times w centered around the pixel. k is a configurable parameter
that weights the effect of standard deviation.
R is the maximum standard deviation of a greyscale image.
Parameters
----------
image: (N, M) ndarray
Grayscale input image.
window_size : int, optional
Odd size of pixel neighborhood window (e.g. 3, 5, 7...).
k : float, optional
Value of the positive parameter k.
r : float, optional
Value of R, the dynamic range of standard deviation.
If None, set to the half of the image dtype range.
offset : float, optional
Constant subtracted from obtained local thresholds.
Returns
-------
threshold : (N, M) ndarray
Threshold mask. All pixels with an intensity higher than
this value are assumed to be foreground.
Notes
-----
This algorithm is originally designed for text recognition.
References
----------
.. [1] J. Sauvola and M. Pietikainen, "Adaptive document image
binarization," Pattern Recognition 33(2),
pp. 225-236, 2000.
DOI:10.1016/S0031-3203(99)00055-2
Examples
--------
>>> from skimage import data
>>> image = data.page()
>>> binary_sauvola = threshold_sauvola(image,
... window_size=15, k=0.2)
"""
if r is None:
imin, imax = dtype_limits(image, clip_negative=False)
r = 0.5 * (imax - imin)
m, s = _mean_std(image, window_size)
return m * (1 + k * ((s / r) - 1))
def imshowg(img, ax=None):
"""Show image using grayscale color map.
"""
vmin, vmax = util.dtype_limits(img, clip_negative=True)
if ax is None:
ax = plt.imshow(img, cmap="gray", vmin=vmin, vmax=vmax)
else:
ax.imshow(img, cmap="gray", vmin=vmin, vmax=vmax)
return ax
def draw_points(size,
num_points,
radius,
seed=1,
func=draw_circle_point,
dtype=np.uint8):
"""
Draw points on the top of an image at random positions.
Parameters
----------
size : tuple of 2 elements
Image size.
num_points : int
Number of points.
radius : int
Point radius.
func : callable, optional
Function to generate points. The function must return a
tuple with point positions and intensities.
seed : int, optional
Seed used to generate random point positions.
Returns
-------
image : (N, M) ndarray
Examples
--------
>>> size = (100, 100)
>>> img = draw_points(size, 100, 4, seed=1, func=draw_circle_point)
"""
np.random.seed(seed)
max_y, max_x = size
imin, imax = dtype_limits(np.zeros((0, ), dtype=dtype),
clip_negative=False)
img = np.ones(size, dtype=dtype) * imin
points_x = np.random.randint(radius,
high=max_x - 1 - radius,
size=num_points)
points_y = np.random.randint(radius,
high=max_y - 1 - radius,
size=num_points)
for px, py in zip(points_x, points_y):
points = func(py, px, radius, dtype=img.dtype)
for rr, cc, intensity in points:
img[rr, cc] = intensity
return img
def remove_small_blobs(bw_img, min_area=35, **label_kwargs):
""" Remove small blobs in the bw img. """
labels = label(bw_img, **label_kwargs)
# pick the background and foreground colors
bg = label_kwargs.get('background', 0)
fg = dtype_limits(bw_img, clip_negative=True)[1] - bg
# create an empty image
new_bw = np.ones_like(bw_img) * bg
# check the area of each region
for roi in regionprops(labels):
if roi.area >= min_area:
new_bw[labels == roi.label] = fg
return new_bw
def visualizeROI(roidict, img, cmap="gray", alpha=0.35, **args):
colors = plt.cm.tab10(np.linspace(0, 1, len(roidict)))
fig, ax = plt.subplots(1, 1)
vmin, vmax = util.dtype_limits(img, clip_negative=True)
ax.imshow(img, cmap=cmap, vmin=vmin, vmax=vmax)
for i, region in enumerate(roidict.values()):
minr, minc, maxr, maxc = region
height = maxr - minr
width = maxc - minc
rect = patches.Rectangle((minc, minr),
width,
height,
alpha=alpha,
color=colors[i],
**args)
ax.add_patch(rect)
return fig, ax
def draw_square_point(cy, cx, halfwidth, dtype=np.uint8):
"""
Draw a point made of concentric squares.
Parameters
----------
cy, cx : int
Center coordinates of the point.
halfwidth : int
Half width of the point.
dtype : numpy dtype
Data type used to generate the intensity values.
Returns
-------
rr, cc, intensity : (N,) ndarray of int
Notes
-----
The intensity decreases linearly along the radial position.
Examples
--------
>>> img = np.zeros((100, 100), dtype=np.uint8)
>>> points = draw_square_point(30, 30, 5)
>>> for rr, cc, intensity in points:
... img[rr, cc] = intensity
"""
imin, imax = dtype_limits(np.zeros((0, ), dtype=dtype),
clip_negative=False)
if dtype in dtypes_float:
intensity_step = (imax - imin) / halfwidth
else:
intensity_step = (imax - imin) // halfwidth
data = []
for pos in range(0, halfwidth):
yi = [cy - pos, cy + pos, cy + pos, cy - pos]
xi = [cx - pos, cx - pos, cx + pos, cx + pos]
pixels = draw.polygon_perimeter(yi, xi)
intensity = imax - pos * intensity_step
intensity = intensity * np.ones(pixels[0].size)
data.append((pixels[0], pixels[1], intensity))
return data
def draw_circle_point(cy, cx, radius, dtype=np.uint8):
"""
Draw a point made of concentric Andres' circles.
Parameters
----------
cy, cx : int
Center coordinates of the point.
radius : int
Radius of the point.
dtype : numpy dtype
Data type used to generate the intensity values.
Returns
-------
rr, cc, intensity : (N,) ndarray of int
Notes
-----
The intensity decreases linearly along the radial position.
Examples
--------
>>> img = np.zeros((100, 100), dtype=np.uint8)
>>> points = draw_circle_point(30, 30, 5)
>>> for rr, cc, intensity in points:
... img[rr, cc] = intensity
"""
imin, imax = dtype_limits(np.zeros((0, ), dtype=dtype),
clip_negative=False)
if dtype in dtypes_float:
intensity_step = (imax - imin) / radius
else:
intensity_step = (imax - imin) // radius
data = []
for rad in range(0, radius):
pixels = draw.circle_perimeter(cy, cx, rad, method='andres')
intensity = imax - rad * intensity_step
intensity = intensity * np.ones(pixels[0].size)
data.append((pixels[0], pixels[1], intensity))
return data
def contrast_stretch(image, min_percentile=2, max_percentile=98):
p2, p98 = np.percentile(image, (min_percentile, max_percentile))
image = exposure.rescale_intensity(image, in_range=(p2, p98))
min_val, max_val = dtype_limits(image, clip_negative=True)
image = np.clip(image, min_val, max_val)
return image
