Python图像处理
以前照相从来没有那么容易。现在你只需要一部手机。拍照是免费的,如果我们不考虑手机的费用的话。就在上一代人之前,业余艺术家和真正的艺术家如果拍照非常昂贵,并且每张照片的成本也不是免费的。
我们拍照是为了及时保存伟大的时刻,被保存的记忆随时准备在未来被"打开"。
就像腌制东西一样,我们要注意正确的防腐剂。当然,手机也为我们提供了一系列的图像处理软件,但是一旦我们需要处理大量的照片,我们就需要其他的工具。这时,编程和Python就派上用场了。Python及其模块如Numpy、Scipy、Matplotlib和其他特殊模块提供了各种各样的函数,能够处理大量图片。
为了向你提供必要的知识,本章的Python教程将处理基本的图像处理和操作。为此,我们使用模块NumPy、Matplotlib和SciPy。
我们从scipy包misc开始。# 以下行仅在Python notebook中需要: %matplotlib inline from scipy import misc ascent = misc.ascent() import matplotlib.pyplot as plt plt.gray() plt.imshow(ascent) plt.show()
除了图像之外,我们还可以看到带有刻度的轴。这可能是非常有趣的,如果你需要一些关于大小和像素位置的方向,但在大多数情况下,你想看到没有这些信息的图像。我们可以通过添加命令plt.axis("off")来去掉刻度和轴:from scipy import misc ascent = misc.ascent() import matplotlib.pyplot as plt plt.axis("off") # 删除轴和刻度 plt.gray() plt.imshow(ascent) plt.show()
我们可以看到这个图像的类型是一个整数数组:ascent.dtype
输出:
dtype("int64")
我们也可以检查图像的大小:ascent.shape
输出:
(512,512)
misc包里还有一张浣熊的图片:import scipy.misc face = scipy.misc.face() print(face.shape) print(face.max) print(face.dtype) plt.axis("off") plt.gray() plt.imshow(face) plt.show() (768, 1024, 3) uint8 import matplotlib.pyplot as plt
matplotlib只支持png图像img = plt.imread("frankfurt.png") print(img[:3]) [[[ 0.41176471 0.56862748 0.80000001] [ 0.40392157 0.56078434 0.79215688] [ 0.40392157 0.56862748 0.79607844] ..., [ 0.48235294 0.62352943 0.81960785] [ 0.47843137 0.627451 0.81960785] [ 0.47843137 0.62352943 0.82745099]] [[ 0.40784314 0.56470591 0.79607844] [ 0.40392157 0.56078434 0.79215688] [ 0.40392157 0.56862748 0.79607844] ..., [ 0.48235294 0.62352943 0.81960785] [ 0.47843137 0.627451 0.81960785] [ 0.48235294 0.627451 0.83137256]] [[ 0.40392157 0.56862748 0.79607844] [ 0.40392157 0.56862748 0.79607844] [ 0.40392157 0.56862748 0.79607844] ..., [ 0.48235294 0.62352943 0.81960785] [ 0.48235294 0.62352943 0.81960785] [ 0.48627451 0.627451 0.83137256]]] plt.axis("off") imgplot = plt.imshow(img) lum_img = img[:,:,1] print(lum_img) [[ 0.56862748 0.56078434 0.56862748 ..., 0.62352943 0.627451 0.62352943] [ 0.56470591 0.56078434 0.56862748 ..., 0.62352943 0.627451 0.627451 ] [ 0.56862748 0.56862748 0.56862748 ..., 0.62352943 0.62352943 0.627451 ] ..., [ 0.31764707 0.32941177 0.32941177 ..., 0.30588236 0.3137255 0.31764707] [ 0.31764707 0.3137255 0.32941177 ..., 0.3019608 0.32156864 0.33725491] [ 0.31764707 0.3019608 0.33333334 ..., 0.30588236 0.32156864 0.33333334]] plt.axis("off") imgplot = plt.imshow(lum_img) 色彩、色度和色调
现在,我们将展示如何给图像着色。色彩是色彩理论的一种表达,是画家常用的一种技法。想到画家而不想到荷兰是很难想象的。所以在下一个例子中,我们使用荷兰风车的图片。windmills = plt.imread("windmills.png") plt.axis("off") plt.imshow(windmills)
输出:
我们现在想给图像着色。我们用白色,这将增加图像的亮度。为此,我们编写了一个Python函数,它接受一个图像和一个百分比值作为参数。设置"百分比"为0不会改变图像,设置为1表示图像将完全变白:import numpy as np import matplotlib.pyplot as plt def tint(imag, percent): """ imag: 图像 percent: 0,图像将保持不变,1,图像将完全变白色,值应该在0~1 """ tinted_imag = imag + (np.ones(imag.shape) - imag) * percent return tinted_imag windmills = plt.imread("windmills.png") tinted_windmills = tint(windmills, 0.8) plt.axis("off") plt.imshow(tinted_windmills)
输出:
阴影是一种颜色与黑色的混合,它减少了亮度。import numpy as np import matplotlib.pyplot as plt def shade(imag, percent): """ imag: 图像 percent: 0,图像将保持不变,1,图像将完全变黑,值应该在0~1 """ tinted_imag = imag * (1 - percent) return tinted_imag windmills = plt.imread("windmills.png") tinted_windmills = shade(windmills, 0.7) plt.imshow(tinted_windmills)
输出: def vertical_gradient_line(image, reverse=False): """ 我们创建一个垂直梯度线。形状 (1, image.shape[1], 3)) 如果reverse为False,则值从0增加到1, 否则,值将从1递减到0。 """ number_of_columns = image.shape[1] if reverse: C = np.linspace(1, 0, number_of_columns) else: C = np.linspace(0, 1, number_of_columns) C = np.dstack((C, C, C)) return C horizontal_brush = vertical_gradient_line(windmills) tinted_windmills = windmills * horizontal_brush plt.axis("off") plt.imshow(tinted_windmills)
输出:
现在,我们将通过将Python函数的reverse参数设置为"True"来从右向左着色图像:def vertical_gradient_line(image, reverse=False): """ 我们创建一个水平梯度线。形状 (1, image.shape[1], 3)) 如果reverse为False,则值从0增加到1, 否则,值将从1递减到0。 """ number_of_columns = image.shape[1] if reverse: C = np.linspace(1, 0, number_of_columns) else: C = np.linspace(0, 1, number_of_columns) C = np.dstack((C, C, C)) return C horizontal_brush = vertical_gradient_line(windmills, reverse=True) tinted_windmills = windmills * horizontal_brush plt.axis("off") plt.imshow(tinted_windmills)
输出: def horizontal_gradient_line(image, reverse=False): """ 我们创建一个垂直梯度线。形状(image.shape[0], 1, 3)) 如果reverse为False,则值从0增加到1, 否则,值将从1递减到0。 """ number_of_rows, number_of_columns = image.shape[:2] C = np.linspace(1, 0, number_of_rows) C = C[np.newaxis,:] C = np.concatenate((C, C, C)).transpose() C = C[:, np.newaxis] return C vertical_brush = horizontal_gradient_line(windmills) tinted_windmills = windmills plt.imshow(tinted_windmills)
输出:
色调是由一种颜色与灰色的混合产生的,或由着色和阴影产生的。charlie = plt.imread("Chaplin.png") plt.gray() print(charlie) plt.imshow(charlie) [[ 0.16470589 0.16862746 0.17647059 ..., 0. 0. 0. ] [ 0.16078432 0.16078432 0.16470589 ..., 0. 0. 0. ] [ 0.15686275 0.15686275 0.16078432 ..., 0. 0. 0. ] ..., [ 0. 0. 0. ..., 0. 0. 0. ] [ 0. 0. 0. ..., 0. 0. 0. ] [ 0. 0. 0. ..., 0. 0. 0. ]]
输出:
给灰度图像着色
:http://scikit-image.org/docs/dev/auto_examples/plot_tinting_grayscale_images.html
在下面的示例中,我们将使用不同的颜色映射。颜色映射可以在
matplotlib.pyplot.cm.datad中找到:plt.cm.datad.keys()
输出:dict_keys(["afmhot", "autumn", "bone", "binary", "bwr", "brg", "CMRmap", "cool", "copper", "cubehelix", "flag", "gnuplot", "gnuplot2", "gray", "hot", "hsv", "jet", "ocean", "pink", "prism", "rainbow", "seismic", "spring", "summer", "terrain", "winter", "nipy_spectral", "spectral", "Blues", "BrBG", "BuGn", "BuPu", "GnBu", "Greens", "Greys", "Oranges", "OrRd", "PiYG", "PRGn", "PuBu", "PuBuGn", "PuOr", "PuRd", "Purples", "RdBu", "RdGy", "RdPu", "RdYlBu", "RdYlGn", "Reds", "Spectral", "YlGn", "YlGnBu", "YlOrBr", "YlOrRd", "gist_earth", "gist_gray", "gist_heat", "gist_ncar", "gist_rainbow", "gist_stern", "gist_yarg", "coolwarm", "Wistia", "Accent", "Dark2", "Paired", "Pastel1", "Pastel2", "Set1", "Set2", "Set3", "tab10", "tab20", "tab20b", "tab20c", "Vega10", "Vega20", "Vega20b", "Vega20c", "afmhot_r", "autumn_r", "bone_r", "binary_r", "bwr_r", "brg_r", "CMRmap_r", "cool_r", "copper_r", "cubehelix_r", "flag_r", "gnuplot_r", "gnuplot2_r", "gray_r", "hot_r", "hsv_r", "jet_r", "ocean_r", "pink_r", "prism_r", "rainbow_r", "seismic_r", "spring_r", "summer_r", "terrain_r", "winter_r", "nipy_spectral_r", "spectral_r", "Blues_r", "BrBG_r", "BuGn_r", "BuPu_r", "GnBu_r", "Greens_r", "Greys_r", "Oranges_r", "OrRd_r", "PiYG_r", "PRGn_r", "PuBu_r", "PuBuGn_r", "PuOr_r", "PuRd_r", "Purples_r", "RdBu_r", "RdGy_r", "RdPu_r", "RdYlBu_r", "RdYlGn_r", "Reds_r", "Spectral_r", "YlGn_r", "YlGnBu_r", "YlOrBr_r", "YlOrRd_r", "gist_earth_r", "gist_gray_r", "gist_heat_r", "gist_ncar_r", "gist_rainbow_r", "gist_stern_r", "gist_yarg_r", "coolwarm_r", "Wistia_r", "Accent_r", "Dark2_r", "Paired_r", "Pastel1_r", "Pastel2_r", "Set1_r", "Set2_r", "Set3_r", "tab10_r", "tab20_r", "tab20b_r", "tab20c_r", "Vega10_r", "Vega20_r", "Vega20b_r", "Vega20c_r"]) import numpy as np import matplotlib.pyplot as plt charlie = plt.imread("Chaplin.png") # colormaps plt.cm.datad # cmaps = set(plt.cm.datad.keys()) cmaps = {"afmhot", "autumn", "bone", "binary", "bwr", "brg", "CMRmap", "cool", "copper", "cubehelix", "Greens"} X = [ (4,3,1, (1, 0, 0)), (4,3,2, (0.5, 0.5, 0)), (4,3,3, (0, 1, 0)), (4,3,4, (0, 0.5, 0.5)), (4,3,(5,8), (0, 0, 1)), (4,3,6, (1, 1, 0)), (4,3,7, (0.5, 1, 0) ), (4,3,9, (0, 0.5, 0.5)), (4,3,10, (0, 0.5, 1)), (4,3,11, (0, 1, 1)), (4,3,12, (0.5, 1, 1))] fig = plt.figure(figsize=(6, 5)) #fig.subplots_adjust(bottom=0, left=0, top = 0.975, right=1) for nrows, ncols, plot_number, factor in X: sub = fig.add_subplot(nrows, ncols, plot_number) sub.set_xticks([]) plt.colors() sub.imshow(charlie*0.0002, cmap=cmaps.pop()) sub.set_yticks([]) #fig.show()