将numpy数组写入png或动画png文件。
numpngw的Python项目详细描述
这个python包定义了函数write_png，该函数编写 numpy数组到一个png文件，函数write_apng写入 动画PNG（APNG）文件的数组序列。也包括 是可用于保存matplotlib的类AnimatedPNGWriter。 动画作为动画PNG文件；参见示例8。
write_png的功能包括：
- 创建8位和16位rgb文件；
- 创建1位、2位、4位、8位和16位灰度文件；
- 使用alpha通道创建rgb和灰度图像；
- 设置透明颜色；
- 为索引PNG文件自动创建调色板；
- 包含^{TT5}$，^{TT6}$，^{TT7}$，^{TT8}$，^{TT9}$，^{TT10}$ 以及iCCP块。
这个包是用纯python编写的。唯一的外部依赖 是numpy和setuptools。
该包有一套单元测试，但仍应考虑 原型质量软件。可能存在向后不兼容的API更改 在释放之间。
本软件在BSD 2条款许可下发布。
对于具有更多功能的包（包括读取png文件的函数）， 看一看：
下面的示例显示了使用 努比和努姆普。要查看示例5-8中的动画，必须查看 此文件带有支持动画PNG文件的浏览器。目前（作为 关于此文件的编写）、Firefox、Safari 10和最新版本的 Chromium支持动画PNG。歌剧需要延期。
示例1
下面的脚本创建这个png文件，一个8位的rgb图像。
脚本：
import numpy as np
from numpngw import write_png
# Example 1
#
# Create an 8-bit RGB image.
img = np.zeros((80, 128, 3), dtype=np.uint8)
grad = np.linspace(0, 255, img.shape[1])
img[:16, :, :] = 127
img[16:32, :, 0] = grad
img[32:48, :, 1] = grad[::-1]
img[48:64, :, 2] = grad
img[64:, :, :] = 127
write_png('example1.png', img)
例2
下面的脚本创建这个png文件，一个1位灰度图像。
脚本：
import numpy as np
from numpngw import write_png
# Example 2
#
# Create a 1-bit grayscale image.
mask = np.zeros((48, 48), dtype=np.uint8)
mask[:2, :] = 1
mask[:, -2:] = 1
mask[4:6, :-4] = 1
mask[4:, -6:-4] = 1
mask[-16:, :16] = 1
mask[-32:-16, 16:32] = 1
write_png('example2.png', mask, bitdepth=1)
例3
下面的脚本创建这个png文件，一个16位的rgb文件，其中 值（0，0，0）是透明的。可能不明显，但是 两个正方形是透明的。
脚本：
import numpy as np
from numpngw import write_png
# Example 3
#
# Create a 16-bit RGB image, with (0, 0, 0) indicating a transparent pixel.
# Create some interesting data.
w = 32
nrows = 3*w
ncols = 5*w
kernel = np.exp(-np.linspace(-2, 2, 35)**2)
kernel = kernel/kernel.sum()
np.random.seed(123)
x = np.random.randn(nrows, ncols, 3)
x = np.apply_along_axis(lambda z: np.convolve(z, kernel, mode='same'), 0, x)
x = np.apply_along_axis(lambda z: np.convolve(z, kernel, mode='same'), 1, x)
# Convert to 16 bit unsigned integers.
z = (65535*((x - x.min())/x.ptp())).astype(np.uint16)
# Create two squares containing (0, 0, 0).
z[w:2*w, w:2*w] = 0
z[w:2*w, -2*w:-w] = 0
# Write the PNG file, and indicate that (0, 0, 0) should be transparent.
write_png('example3.png', z, transparent=(0, 0, 0))
例4
下面的脚本使用选项use_palette=True创建这个8位 索引的rgb文件。
脚本：
import numpy as np
from numpngw import write_png
# Example 4
#
# Create an 8-bit indexed RGB image that uses a palette.
img_width = 300
img_height = 200
img = np.zeros((img_height, img_width, 3), dtype=np.uint8)
np.random.seed(222)
for _ in range(40):
width = np.random.randint(5, img_width // 5)
height = np.random.randint(5, img_height // 5)
row = np.random.randint(5, img_height - height - 5)
col = np.random.randint(5, img_width - width - 5)
color = np.random.randint(80, 256, size=2)
img[row:row+height, col:col+width, 1:] = color
write_png('example4.png', img, use_palette=True)
例5
此动画PNG
由以下脚本创建。在其他例子中，大多数 脚本是生成要保存的数据的代码。创建 png文件很简单：
write_apng("example5.png", seq, delay=50, use_palette=True)
脚本：
import numpy as np
from numpngw import write_apng
# Example 5
#
# Create an 8-bit RGB animated PNG file.
height = 20
width = 200
t = np.linspace(0, 10*np.pi, width)
seq = []
for phase in np.linspace(0, 2*np.pi, 25, endpoint=False):
y = 150*0.5*(1 + np.sin(t - phase))
a = np.zeros((height, width, 3), dtype=np.uint8)
a[:, :, 0] = y
a[:, :, 2] = y
seq.append(a)
write_apng("example5.png", seq, delay=50, use_palette=True)
例6
另一个动画rgb png。在本例中，参数seq 传递给write_apng的是具有形状的numpy数组 (num_frames, height, width, 3)。
脚本：
import numpy as np
from numpngw import write_apng
# Example 6
#
# Create an 8-bit RGB animated PNG file.
def smoother(w):
# Return the periodic convolution of w with a 3-d Gaussian kernel.
r = np.linspace(-3, 3, 21)
X, Y, Z = np.meshgrid(r, r, r)
kernel = np.exp(-0.25*(X*X + Y*Y + Z*Z)**2)
fw = np.fft.fftn(w)
fkernel = np.fft.fftn(kernel, w.shape)
v = np.fft.ifftn(fw*fkernel).real
return v
height = 40
width = 250
num_frames = 30
np.random.seed(12345)
w = np.random.randn(num_frames, height, width, 3)
for k in range(3):
w[..., k] = smoother(w[..., k])
seq = (255*(w - w.min())/w.ptp()).astype(np.uint8)
write_apng("example6.png", seq, delay=40)
例7
创建一个动画PNG，每帧显示时间不同。
脚本：
import numpy as np
from numpngw import write_apng
# Example 7
#
# Create an animated PNG file with nonuniform display times
# of the frames.
bits1 = np.array([
[0,0,1,0,0],
[0,1,1,0,0],
[0,0,1,0,0],
[0,0,1,0,0],
[0,0,1,0,0],
[0,0,1,0,0],
[0,1,1,1,0],
])
bits2 = np.array([
[0,1,1,1,0],
[1,0,0,0,1],
[0,0,0,0,1],
[0,1,1,1,0],
[1,0,0,0,0],
[1,0,0,0,0],
[1,1,1,1,1],
])
bits3 = np.array([
[0,1,1,1,0],
[1,0,0,0,1],
[0,0,0,0,1],
[0,0,1,1,0],
[0,0,0,0,1],
[1,0,0,0,1],
[0,1,1,1,0],
])
bits_box1 = np.array([
[0,0,0,0,0],
[1,1,1,1,1],
[1,0,0,0,1],
[1,0,0,0,1],
[1,0,0,0,1],
[1,1,1,1,1],
[0,0,0,0,0],
])
bits_box2 = np.array([
[0,0,0,0,0],
[0,0,0,0,0],
[0,1,1,1,0],
[0,1,0,1,0],
[0,1,1,1,0],
[0,0,0,0,0],
[0,0,0,0,0],
])
bits_dot = np.array([
[0,0,0,0,0],
[0,0,0,0,0],
[0,0,0,0,0],
[0,0,1,0,0],
[0,0,0,0,0],
[0,0,0,0,0],
[0,0,0,0,0],
])
bits_zeros = np.zeros((7, 5), dtype=bool)
bits_ones = np.ones((7, 5), dtype=bool)
def bits_to_image(bits, blocksize=32, color=None):
bits = np.asarray(bits, dtype=np.bool)
if color is None:
color = np.array([255, 0, 0], dtype=np.uint8)
else:
color = np.asarray(color, dtype=np.uint8)
x = np.linspace(-1, 1, blocksize)
X, Y = np.meshgrid(x, x)
Z = np.sqrt(np.maximum(1 - (X**2 + Y**2), 0))
# The "on" image:
img1 = (Z.reshape(blocksize, blocksize, 1)*color)
# The "off" image:
img0 = 0.2*img1
data = np.where(bits[:, None, :, None, None],
img1[:, None, :], img0[:, None, :])
img = data.reshape(bits.shape[0]*blocksize, bits.shape[1]*blocksize, 3)
return img.astype(np.uint8)
# Create `seq` and `delay`, the sequence of images and the
# corresponding display times.
color = np.array([32, 48, 255])
blocksize = 24
# Images...
im3 = bits_to_image(bits3, blocksize=blocksize, color=color)
im2 = bits_to_image(bits2, blocksize=blocksize, color=color)
im1 = bits_to_image(bits1, blocksize=blocksize, color=color)
im_all = bits_to_image(bits_ones, blocksize=blocksize, color=color)
im_none = bits_to_image(bits_zeros, blocksize=blocksize, color=color)
im_box1 = bits_to_image(bits_box1, blocksize=blocksize, color=color)
im_box2 = bits_to_image(bits_box2, blocksize=blocksize, color=color)
im_dot = bits_to_image(bits_dot, blocksize=blocksize, color=color)
# The sequence of images:
seq = [im3, im2, im1, im_all, im_none, im_all, im_none, im_all, im_none,
im_box1, im_box2, im_dot, im_none]
# The time duration to display each image, in milliseconds:
delay = [1000, 1000, 1000, 333, 250, 333, 250, 333, 500,
167, 167, 167, 1000]
# Create the animated PNG file.
write_apng("example7.png", seq, delay=delay, default_image=im_all,
use_palette=True)
例8
此示例显示如何将matplotlib动画另存为 带有numpngw.animatedpngwriter的动画PNG文件。（小心 有了这个类，它可以轻松地创建非常大的png文件。）
脚本：
import numpy as np
from scipy.integrate import odeint
from scipy.fftpack import diff as psdiff
import matplotlib.pyplot as plt
from matplotlib import animation
from numpngw import AnimatedPNGWriter
def kdv_exact(x, c):
"""
Profile of the exact solution to the KdV for a single soliton
on the real line.
"""
u = 0.5*c*np.cosh(0.5*np.sqrt(c)*x)**(-2)
return u
def kdv(u, t, L):
"""
Differential equations for the KdV equation, discretized in x.
"""
# Compute the x derivatives using the pseudo-spectral method.
ux = psdiff(u, period=L)
uxxx = psdiff(u, period=L, order=3)
# Compute du/dt.
dudt = -6*u*ux - uxxx
return dudt
def kdv_solution(u0, t, L):
"""
Use odeint to solve the KdV equation on a periodic domain.
`u0` is initial condition, `t` is the array of time values at which
the solution is to be computed, and `L` is the length of the periodic
domain.
"""
sol = odeint(kdv, u0, t, args=(L,), mxstep=5000)
return sol
def update_line(num, x, data, line):
"""
Animation "call back" function for each frame.
"""
line.set_data(x, data[num, :])
return line,
# Set the size of the domain, and create the discretized grid.
L = 80.0
N = 256
dx = L / (N - 1.0)
x = np.linspace(0, (1-1.0/N)*L, N)
# Set the initial conditions.
# Not exact for two solitons on a periodic domain, but close enough...
u0 = kdv_exact(x-0.15*L, 0.8) + kdv_exact(x-0.4*L, 0.4)
# Set the time sample grid.
T = 260
t = np.linspace(0, T, 225)
print("Computing the solution.")
sol = kdv_solution(u0, t, L)
print("Generating the animated PNG file.")
fig = plt.figure(figsize=(7.5, 1.5))
ax = fig.gca(title="Korteweg de Vries interacting solitons in a periodic "
"domain (L = 80)")
# Plot the initial condition. lineplot is reused in the animation.
lineplot, = ax.plot(x, u0, 'c-', linewidth=3)
plt.tight_layout()
ani = animation.FuncAnimation(fig, update_line, frames=len(t),
init_func=lambda : None,
fargs=(x, sol, lineplot))
writer = AnimatedPNGWriter(fps=12)
ani.save('kdv.png', dpi=60, writer=writer)
plt.close(fig)
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