# PyCUDAラプラシアンフィルタ完成版を使って速度比較

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## Introducing the discrete Laplacian¶

import skimage.data
import skimage.color
from skimage.filters import laplace
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

image = skimage.data.astronaut()
image = skimage.color.rgb2gray(image)
print(image.shape)
print(image.dtype)

(512, 512)
float64

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## Scikit-Image implementation¶

def laplace_skimage(image):
"""Applies Laplace operator to 2D image using skimage implementation.
Then tresholds the result and returns boolean image."""
laplacian = laplace(image)
thresh = np.abs(laplacian) > 0.05
return thresh

edges = laplace_skimage(image)
edges.shape

(512, 512)
def compare(left, right):
"""Compares two images, left and right."""
fig, ax = plt.subplots(1, 2, figsize=(20, 10))
ax[0].imshow(left, cmap='gray')
ax[1].imshow(right, cmap='gray')

compare(left=image, right=edges)

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## NumPy implementation¶

def laplace_numpy(image):
"""Applies Laplace operator to 2D image using our own NumPy implementation.
Then tresholds the result and returns boolean image."""
laplacian = image[:-2, 1:-1] + image[2:, 1:-1] + image[1:-1, :-2] + image[1:-1, 2:] - 4*image[1:-1, 1:-1]
thresh = np.abs(laplacian) > 0.05
return thresh

laplace_numpy(image).shape

(510, 510)
compare(image, laplace_numpy(image))

np.allclose(laplace_skimage(image)[1:-1, 1:-1], laplace_numpy(image))

True
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## Cython¶

%load_ext cython

%%cython
import numpy as np
cimport numpy as cnp
import cython

@cython.boundscheck(False) # turn off bounds-checking for entire function
@cython.wraparound(False)  # turn off negative index wrapping for entire function
def laplace_cython(cnp.ndarray[double, ndim=2] image):
"""Applies Laplace operator to 2D image, then tresholds the result and returns boolean image.
Cython implementation."""
cdef int h = image.shape[0]
cdef int w = image.shape[1]
cdef cnp.ndarray[double, ndim=2] laplacian = np.empty((w-2, h-2), dtype=np.double)
cdef int i, j
for i in range(1, h-1):
for j in range(1, w-1):
laplacian[i-1, j-1] = image[i-1, j] + image[i+1, j] + image[i, j-1] + image[i, j+1] - 4*image[i, j]
thresh = np.abs(laplacian) > 0.05
return thresh

np.allclose(laplace_numpy(image), laplace_cython(image))

True
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## Pythran¶

%load_ext pythran.magic

%%pythran
#pythran export laplace_pythran_highlevel(float[][])
import numpy as np
def laplace_pythran_highlevel(image):
"""Laplace operator in NumPy for 2D images. Pythran accelerated."""
laplacian = image[:-2, 1:-1] + image[2:, 1:-1] + image1 + image2 - 4*image3
thresh = np.abs(laplacian) > 0.05
return thresh

np.allclose(laplace_numpy(image), laplace_pythran_highlevel(image))

True
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## Numba¶

from numba import jit

@jit(nopython=True, fastmath = True, parallel = True, nogil = True)
def laplace_numba(image):
"""Laplace operator for 2D images. Numba accelerated."""
h = image.shape[0]
w = image.shape[1]
laplacian = np.empty((h - 2, w - 2))
for i in range(1, h - 1):
for j in range(1, w - 1):
laplacian[i-1, j-1] = np.abs(image[i-1, j] + image[i+1, j] + image[i, j-1] + image[i, j+1] - 4*image[i, j]) > 0.05
return laplacian

np.allclose(laplace_numpy(image), laplace_numba(image))

True
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## numba guvectorize¶

from numba import guvectorize

@guvectorize('void(float64[:, :], float64[:, :])', "(m, n)->(m, n)", \
nopython=True, fastmath = True)
def laplace_numba_guvectorize(image, laplacian):
"""Laplace operator in NumPy for 2D images. Numba accelerated."""
h = image.shape[0]
w = image.shape[1]
for i in range(1, h - 1):
for j in range(1, w - 1):
laplacian[i-1, j-1] = np.abs(4 * image[i, j] - image[i - 1, j] - \
image[i + 1, j] - image[i, j + 1] - image[i, j - 1]) > 0.05

laplacian = np.empty_like(image)

laplace_numba_guvectorize(image, laplacian);

np.allclose(laplace_numpy(image), laplacian[:-2, :-2])

True
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## PyCUDA¶

import pycuda.gpuarray as gpuarray
import pycuda.driver as cuda
import pycuda.autoinit
from pycuda.compiler import SourceModule

image = image.astype(np.float32)
(h,w)=image.shape
print (h,w)
print (image.dtype)

mod_copy_texture=SourceModule(
"""
texture<float,2>tex;
__global__ void  copy_texture_kernel(float *C,float * data)
{
int h=C[0];
int w=C4;
while(i<w-1 && j<h-1)
{
data[(i-1)+w*(j-1)] = abs(4*tex2D(tex,j,i)-tex2D(tex,j-1,i)-tex2D(tex,j+1,i)\
-tex2D(tex,j,i+1)-tex2D(tex,j,i-1)) > 0.05;
j += blockDim.y * gridDim.y;
i += blockDim.x * gridDim.x;
}
}
""")
copy_texture_func = mod_copy_texture.get_function("copy_texture_kernel")
texref = mod_copy_texture.get_texref("tex")
cuda.matrix_to_texref(image , texref , order = "F")
#gpu_output = np.empty_like(image)
a_gpu = gpuarray.to_gpu(np.array([image.shape],dtype = np.float32))
c_gpu = gpuarray.to_gpu(np.empty_like(image))
copy_texture_func(a_gpu,c_gpu,\
block=(32,32,1), grid=(h//32,w//32,1), texrefs=[texref])

512 512
float32

%timeit copy_texture_func(a_gpu,c_gpu,\
block=(16,16,1), grid=(h//16,w//16,1), texrefs=[texref])

28.6 µs ± 195 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

compare(c_gpu.get(), laplace_numpy(image))

np.allclose(laplace_numpy(image), c_gpu.get()[:-2, :-2])

True
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## Wrap-up and plots¶

timings = {}
for func in [laplace_skimage, laplace_numpy, laplace_cython, laplace_pythran_highlevel, laplace_numba]:
t = %timeit -o func(image)
timings[func.__name__] = t

2.25 ms ± 16.3 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
1.08 ms ± 17.5 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
516 µs ± 6.31 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
321 µs ± 604 ns per loop (mean ± std. dev. of 7 runs, 1000 loops each)
154 µs ± 262 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

t = %timeit -o laplace_numba_guvectorize(image, laplacian);
timings['laplace_numba_guvectorize'] = t

363 µs ± 2.24 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

t = %timeit -o copy_texture_func(a_gpu,c_gpu,\
block=(16,16,1), grid=(h//16,w//16,1), texrefs=[texref]);
timings['laplace_pycuda'] = t

26.8 µs ± 254 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

import pandas as pd

pd.Series({key: timings[key].average * \
1e6 for key in timings}).to_frame(name='timings (μs)').\
sort_values(by='timings (μs)')

timings (μs)
laplace_pycuda 26.836729
laplace_numba 154.318407
laplace_pythran_highlevel 321.117471
laplace_numba_guvectorize 363.161995
laplace_cython 515.931875
laplace_numpy 1083.795276
laplace_skimage 2254.967624
fig, ax = plt.subplots(figsize=(20, 12))
plt.rcParams["font.size"] = "25"
pd.Series({key: timings[key].average * \
1e6 for key in timings}).to_frame(name='timings (μs)').\
sort_values(by='timings (μs)').plot(kind='barh', ax=ax)

<matplotlib.axes._subplots.AxesSubplot at 0x7f2565c0a6a0>

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