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过滤 :是信号和图像处理中基本的任务。其目的是根据应用环境的不同,选择性的提取图像中某些认为是重要的信息。过滤可以移除图像中的噪音、提取感兴趣的可视特征、允许图像重采样等等。
频域分析 :将图像分成从低频到高频的不同部分。低频对应图像强度变化小的区域,而高频是图像强度变化非常大的区域。
在频率分析领域的框架中,滤波器是一个用来增强图像中某个波段或频率并阻塞(或降低)其他频率波段的操作。低通滤波器是消除图像中高频部分,但保留低频部分。高通滤波器消除低频部分。
滤波(高通、低通、带通、带阻) 、模糊、去噪、平滑等。
图像在频域里面,频率低的地方说明它是比较平滑的,因为平滑的地方灰度值变化比较小
,而频率高的地方通常是边缘或者噪声,因为这些地方往往是灰度值突变的。
高通滤波
就是保留频率比较高的部分,即突出边缘;低通滤波
就是保留频率比较低的地方,即平滑图像,弱化边缘,消除噪声。在pytorch中实现将sobel算子和卷积层结合来提取图像中物体的边缘轮廓图,如下代码是卷积执行soble边缘检测算子的实现:
- import torch
- import numpy as np
- from torch import nn
- from PIL import Image
- from torch.autograd import Variable
- import torch.nn.functional as F
-
- # https://blog.csdn.net/weicao1990/article/details/100521530
-
- def nn_conv2d(im):
- # 用nn.Conv2d定义卷积操作
- conv_op = nn.Conv2d(1, 1, 3, bias=False)
- # 定义sobel算子参数
- sobel_kernel = np.array([[-1, -1, -1], [-1, 8, -1], [-1, -1, -1]], dtype='float32')
- # 将sobel算子转换为适配卷积操作的卷积核
- sobel_kernel = sobel_kernel.reshape((1, 1, 3, 3))
- # 给卷积操作的卷积核赋值
- conv_op.weight.data = torch.from_numpy(sobel_kernel)
- # 对图像进行卷积操作
- edge_detect = conv_op(Variable(im))
- # 将输出转换为图片格式
- edge_detect = edge_detect.squeeze().detach().numpy()
- return edge_detect
-
- def functional_conv2d(im):
- sobel_kernel = np.array([[-1, -1, -1], [-1, 8, -1], [-1, -1, -1]], dtype='float32') #
- sobel_kernel = sobel_kernel.reshape((1, 1, 3, 3))
- weight = Variable(torch.from_numpy(sobel_kernel))
- edge_detect = F.conv2d(Variable(im), weight)
- edge_detect = edge_detect.squeeze().detach().numpy()
- return edge_detect
-
- def main():
- # 读入一张图片,并转换为灰度图
- im = Image.open('./cat.jpg').convert('L')
- # 将图片数据转换为矩阵
- im = np.array(im, dtype='float32')
- # 将图片矩阵转换为pytorch tensor,并适配卷积输入的要求
- im = torch.from_numpy(im.reshape((1, 1, im.shape[0], im.shape[1])))
- # 边缘检测操作
- # edge_detect = nn_conv2d(im)
- edge_detect = functional_conv2d(im)
- # 将array数据转换为image
- im = Image.fromarray(edge_detect)
- # image数据转换为灰度模式
- im = im.convert('L')
- # 保存图片
- im.save('edge.jpg', quality=95)
-
- if __name__ == "__main__":
- main()
效果展示:
四种算子:
- '''
- 滤波与卷积
- '''
- # https://blog.csdn.net/m0_43609475/article/details/112447397
-
- import cv2
- import numpy as np
- import matplotlib.pyplot as plt
-
- def Padding(image,kernels_size,stride = [1,1],padding = "same"):
- '''
- 对图像进行padding
- :param image: 要padding的图像矩阵
- :param kernels_size: list 卷积核大小[h,w]
- :param stride: 卷积步长 [左右步长,上下步长]
- :param padding: padding方式
- :return: padding后的图像
- '''
- if padding == "same":
- h,w = image.shape
- p_h =max((stride[0]*(h-1)-h+kernels_size[0]),0) # 高度方向要补的0
- p_w =max((stride[1]*(w-1)-w+kernels_size[1]),0) # 宽度方向要补的0
- p_h_top = p_h//2 # 上边要补的0
- p_h_bottom = p_h-p_h_top # 下边要补的0
- p_w_left = p_w//2 # 左边要补的0
- p_w_right = p_w-p_w_left # 右边要补的0
- # print(p_h_top,p_h_bottom,p_w_left,p_w_right) # 输出padding方式
- padding_image = np.zeros((h+p_h, w+p_w), dtype=np.uint8)
- for i in range(h):
- for j in range(w):
- padding_image[i+p_h_top][j+p_w_left] = image[i][j] # 将原来的图像放入新图中做padding
- return padding_image
- else:
- return image
-
-
- def filtering_and_convolution(image,kernels,stride,padding = "same"):
- '''
- :param image: 要卷积的图像
- :param kernels: 卷积核 列表
- :param stride: 卷积步长 [左右步长,上下步长]
- :param padding: padding方式 “same”or“valid”
- :return:
- '''
- image_h,image_w = image.shape
- kernels_h,kernels_w = np.array(kernels).shape
- # 获取卷积核的中心点
- kernels_h_core = int(kernels_h/2+0.5)-1
- kernels_w_core = int(kernels_w/2+0.5)-1
- if padding == "valid":
- # 计算卷积后的图像大小
- h = int((image_h-kernels_h)/stride[0]+1)
- w = int((image_w-kernels_w)/stride[1]+1)
- # 生成卷积后的图像
- conv_image = np.zeros((h,w),dtype=np.uint8)
- # 计算遍历起始点
- h1_start = kernels_h//2
- w1_start = kernels_w//2
- ii=-1
- for i in range(h1_start,image_h - h1_start,stride[0]):
- ii += 1
- jj = 0
- for j in range(w1_start,image_w - w1_start,stride[1]):
- sum = 0
- for x in range(kernels_h):
- for y in range(kernels_w):
- # print(i,j,int((i/image_h)*h),int((j/image_w)*w), i-kernels_h_core + x, j-kernels_w_core+y,x,y)
- sum += int(image[i-kernels_h_core+x][j-kernels_w_core+y]*kernels[x][y])
- conv_image[ii][jj] = sum
- jj += 1
- return conv_image
-
- if padding == "same":
- # 对原图进行padding
- kernels_size = [kernels_h, kernels_w]
- pad_image = Padding(image,kernels_size,stride,padding="same")
- # 计算卷积后的图像大小
- h = image_h
- w = image_w
- # 生成卷积后的图像
- conv_image = np.zeros((h,w),dtype=np.uint8)
- # # 计算遍历起始点
- h1_start = kernels_h//2
- w1_start = kernels_w//2
- ii=-1
- for i in range(h1_start,image_h - h1_start,stride[0]):
- ii +=1
- jj = 0
- for j in range(w1_start,image_w - w1_start,stride[1]):
- sum = 0
- for x in range(kernels_h):
- for y in range(kernels_w):
- sum += int(image[i-kernels_h_core+x][j-kernels_w_core+y]*kernels[x][y])
- conv_image[ii][jj] = sum
- jj += 1
- return conv_image
-
- def sobel_filter(image):
- h = image.shape[0]
- w = image.shape[1]
- image_new = np.zeros(image.shape, np.uint8)
-
- for i in range(1, h - 1):
- for j in range(1, w - 1):
- sx = (image[i + 1][j - 1] + 2 * image[i + 1][j] + image[i + 1][j + 1]) - \
- (image[i - 1][j - 1] + 2 * image[i - 1][j] + image[i - 1][j + 1])
- sy = (image[i - 1][j + 1] + 2 * image[i][j + 1] + image[i + 1][j + 1]) - \
- (image[i - 1][j - 1] + 2 * image[i][j - 1] + image[i + 1][j - 1])
- image_new[i][j] = np.sqrt(np.square(sx) + np.square(sy))
- # image_new[i][j] = sy
- return image_new
-
- # 设置matplotlib正常显示中文和负号
- plt.rcParams['font.sans-serif']=['SimHei'] # 用黑体显示中文
- plt.rcParams['axes.unicode_minus']=False # 正常显示负号
- img = cv2.imread('lenna.png',1)
- img_gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
- plt.subplot(331)
- plt.imshow(img_gray,cmap="gray")
- plt.title("原图")
-
-
- sobel_Gy = [[-1,0,1],[-2,0,2],[-1,0,1]]
- Average = [[1/9,1/9,1/9],[1/9,1/9,1/9],[1/9,1/9,1/9]]
- Gaussian = [[1/16,2/16,1/16],[2/16,4/16,2/16],[1/16,2/16,1/16]]
- Laplace = [[-1,-1,-1],[-1,9,-1],[-1,-1,-1]]
- stride=[1,1]
- img_sobel_Gy = filtering_and_convolution(img_gray,sobel_Gy,stride,padding="same")
- img_Average = filtering_and_convolution(img_gray,Average,stride,padding="same")
- img_Gaussian = filtering_and_convolution(img_gray,Gaussian,stride,padding="same")
- img_Laplace = filtering_and_convolution(img_gray,Laplace,stride,padding="same")
- plt.subplot(332)
- plt.imshow(img_sobel_Gy,cmap = "gray")
- plt.title("sobel_Gy")
- plt.subplot(333)
- plt.imshow(img_Average,cmap = "gray")
- plt.title("Average")
- plt.subplot(334)
- plt.imshow(img_Gaussian,cmap = "gray")
- plt.title("Gaussian")
- plt.subplot(335)
- plt.imshow(img_Laplace,cmap = "gray")
- plt.title("Laplace")
- plt.show()
- import cv2
- import numpy as np
-
- # https://wangsp.blog.csdn.net/article/details/82872838
-
- def blur_demo(image):
- """
- 均值模糊 : 去随机噪声有很好的去噪效果
- (1, 15)是垂直方向模糊,(15, 1)是水平方向模糊
- """
- dst = cv2.blur(image, (1, 15))
- cv2.imshow("avg_blur_demo", dst)
-
- def median_blur_demo(image): # 中值模糊 对椒盐噪声有很好的去燥效果
- dst = cv2.medianBlur(image, 5)
- cv2.imshow("median_blur_demo", dst)
-
- def custom_blur_demo(image):
- """
- 用户自定义模糊
- 下面除以25是防止数值溢出
- """
- kernel = np.ones([5, 5], np.float32)/25
- dst = cv2.filter2D(image, -1, kernel)
- cv2.imshow("custom_blur_demo", dst)
-
- src = cv2.imread("./fapiao.png")
- img = cv2.resize(src,None,fx=0.8,fy=0.8,interpolation=cv2.INTER_CUBIC)
- cv2.imshow('input_image', img)
-
- blur_demo(img)
- median_blur_demo(img)
- custom_blur_demo(img)
-
- cv2.waitKey(0)
- cv2.destroyAllWindows()
进行边缘保留滤波通常用到两个方法:高斯双边滤波和均值迁移滤波。
- """
- bilateralFilter(src, d, sigmaColor, sigmaSpace[, dst[, borderType]]) -> dst
- - src: 输入图像。
- - d: 在过滤期间使用的每个像素邻域的直径。如果输入d非0,则sigmaSpace由d计算得出,如果sigmaColor没输入,则sigmaColor由sigmaSpace计算得出。
- - sigmaColor: 色彩空间的标准方差,一般尽可能大。
- 较大的参数值意味着像素邻域内较远的颜色会混合在一起,
- 从而产生更大面积的半相等颜色。
- - sigmaSpace: 坐标空间的标准方差(像素单位),一般尽可能小。
- 参数值越大意味着只要它们的颜色足够接近,越远的像素都会相互影响。
- 当d > 0时,它指定邻域大小而不考虑sigmaSpace。
- 否则,d与sigmaSpace成正比。
- """
- import cv2
-
- def bi_demo(image): #双边滤波
- dst = cv2.bilateralFilter(image, 0, 100, 5)
- cv2.imshow("bi_demo", dst)
-
- def shift_demo(image): #均值迁移
- dst = cv2.pyrMeanShiftFiltering(image, 10, 50)
- cv2.imshow("shift_demo", dst)
-
- src = cv2.imread('./100.png')
- img = cv2.resize(src,None,fx=0.8,fy=0.8,
- interpolation=cv2.INTER_CUBIC)
- cv2.imshow('input_image', img)
-
- bi_demo(img)
- shift_demo(img)
-
- cv2.waitKey(0)
- cv2.destroyAllWindows()
- import cv2
- import numpy as np
-
- def salt(img, n):
- for k in range(n):
- i = int(np.random.random() * img.shape[1])
- j = int(np.random.random() * img.shape[0])
- if img.ndim == 2:
- img[j,i] = 255
- elif img.ndim == 3:
- img[j,i,0]= 255
- img[j,i,1]= 255
- img[j,i,2]= 255
- return img
-
- img = cv2.imread("./original_img.png",cv2.IMREAD_GRAYSCALE)
- result = salt(img, 500)
- median = cv2.medianBlur(result, 5)
- cv2.imshow("original_img", img)
- cv2.imshow("Salt", result)
- cv2.imshow("Median", median)
- cv2.waitKey(0)
- cv2.destroyWindow()
- import cv2
- import numpy as np
-
- def clamp(pv):
- if pv > 255:
- return 255
- if pv < 0:
- return 0
- else:
- return pv
-
- def gaussian_noise(image): # 加高斯噪声
- h, w, c = image.shape
- for row in range(h):
- for col in range(w):
- s = np.random.normal(0, 20, 3)
- b = image[row, col, 0] # blue
- g = image[row, col, 1] # green
- r = image[row, col, 2] # red
- image[row, col, 0] = clamp(b + s[0])
- image[row, col, 1] = clamp(g + s[1])
- image[row, col, 2] = clamp(r + s[2])
- cv2.imshow("noise image", image)
-
- src = cv2.imread('888.png')
- cv2.imshow('input_image', src)
-
- gaussian_noise(src)
- dst = cv2.GaussianBlur(src, (15,15), 0) #高斯模糊
- cv2.imshow("Gaussian_Blur2", dst)
-
- cv2.waitKey(0)
- cv2.destroyAllWindows()
使用的函数有:cv2.Sobel()
, cv2.Schar()
, cv2.Laplacian()
Sobel,scharr其实是求一阶或者二阶导数。scharr是对Sobel的优化。
Laplacian是求二阶导数。
- """
- dst = cv2.Sobel(src, ddepth, dx, dy[, dst[, ksize[, scale[, delta[, borderType]]]]])
- src: 需要处理的图像;
- ddepth: 图像的深度,-1表示采用的是与原图像相同的深度。
- 目标图像的深度必须大于等于原图像的深度;
- dx和dy: 求导的阶数,0表示这个方向上没有求导,一般为0、1、2。
- dst 不用解释了;
- ksize: Sobel算子的大小,必须为1、3、5、7。 ksize=-1时,会用3x3的Scharr滤波器,
- 它的效果要比3x3的Sobel滤波器要好
- scale: 是缩放导数的比例常数,默认没有伸缩系数;
- delta: 是一个可选的增量,将会加到最终的dst中, 默认情况下没有额外的值加到dst中
- borderType: 是判断图像边界的模式。这个参数默认值为cv2.BORDER_DEFAULT。
- """
- import cv2
-
- img=cv2.imread('888.png',cv2.IMREAD_COLOR)
- x=cv2.Sobel(img,cv2.CV_16S,1,0)
- y=cv2.Sobel(img,cv2.CV_16S,0,1)
-
- absx=cv2.convertScaleAbs(x)
- absy=cv2.convertScaleAbs(y)
- dist=cv2.addWeighted(absx,0.5,absy,0.5,0)
-
- cv2.imshow('original_img',img)
- cv2.imshow('y',absy)
- cv2.imshow('x',absx)
- cv2.imshow('dsit',dist)
-
- cv2.waitKey(0)
- cv2.destroyAllWindows()
- import matplotlib.pyplot as plt
- import numpy as np
- import cv2
-
-
- def log_filter(gray_img):
- gaus_img = cv2.GaussianBlur(gray_img,(3,3),sigmaX=0) # 以核大小为3x3,方差为0
- log_img = cv2.Laplacian(gaus_img,cv2.CV_16S,ksize=3) # laplace检测
- log_img = cv2.convertScaleAbs(log_img)
- return log_img
-
-
- def filter_imgs(gray_img):
- # 尝试一下不同的核的效果
- Emboss = np.array([[ -2,-1, 0],
- [ -1, 1, 1],
- [ 0, 1, 2]])
-
- Motion = np.array([[ 0.333, 0, 0],
- [ 0, 0.333, 0],
- [ 0, 0, 0.333]])
-
- Emboss_img = cv2.filter2D(gray_img,cv2.CV_16S,Emboss)
- Motion_img = cv2.filter2D(gray_img, cv2.CV_16S, Motion)
- Emboss_img = cv2.convertScaleAbs(Emboss_img)
- Motion_img = cv2.convertScaleAbs(Motion_img)
-
- different_V = np.array([[ 0, -1, 0],
- [ 0, 1, 0],
- [ 0, 0, 0]])
- different_H = np.array([[ 0, 0, 0],
- [ -1, 1, 0],
- [ 0, 0, 0]])
- different_temp = cv2.filter2D(gray_img,cv2.CV_16S,different_V)
- different_temp = cv2.filter2D(different_temp, cv2.CV_16S, different_H)
- different_img = cv2.convertScaleAbs(different_temp)
-
- Sobel_V = np.array([[ 1, 2, 1],
- [ 0, 0, 0],
- [ -1, -2, -1]])
- Sobel_H = np.array([[ 1, 0, -1],
- [ 2, 0, -2],
- [ 1, 0, -1]])
- Sobel_temp = cv2.filter2D(gray_img,cv2.CV_16S, Sobel_V)
- Sobel_temp = cv2.filter2D(Sobel_temp, cv2.CV_16S, Sobel_H)
- Sobel_img = cv2.convertScaleAbs(Sobel_temp)
-
-
- Prewitt_V = np.array([[-1, -1, -1],
- [ 0, 0, 0],
- [ 1, 1, 1]])
- Prewitt_H = np.array([[-1, 0, 1],
- [-1, 0, 1],
- [-1, 0, 1]])
- Prewitt_temp = cv2.filter2D(gray_img, cv2.CV_16S, Prewitt_V)
- Prewitt_temp = cv2.filter2D(Prewitt_temp, cv2.CV_16S, Prewitt_H)
- Prewitt_img = cv2.convertScaleAbs(Prewitt_temp)
-
- kernel_P = np.array([[0, 0, -1, 0, 0],
- [0, -1, -2, -1, 0],
- [-1,-2, 16, -2,-1],
- [0, -1, -2, -1, 0],
- [0, 0, -1, 0, 0]])
- kernel_N = np.array([[0, 0, 1, 0, 0],
- [0, 1, 2, 1, 0],
- [1, 2, -16, 2, 1],
- [0, 1, 2, 1, 0],
- [0, 0, 1, 0, 0]])
-
-
- lap4_filter = np.array([[0, 1, 0],
- [1, -4, 1],
- [0, 1, 0]]) # 4邻域laplacian算子
- lap8_filter = np.array([[0, 1, 0],
- [1, -8, 1],
- [0, 1, 0]]) # 8邻域laplacian算子
- lap_filter_P = cv2.filter2D(gray_img, cv2.CV_16S, kernel_P)
- edge4_img_P = cv2.filter2D(lap_filter_P, cv2.CV_16S, lap4_filter)
- edge4_img_P = cv2.convertScaleAbs(edge4_img_P)
-
- edge8_img_P = cv2.filter2D(lap_filter_P, cv2.CV_16S, lap8_filter)
- edge8_img_P = cv2.convertScaleAbs(edge8_img_P)
-
-
- lap_filter_N = cv2.filter2D(gray_img, cv2.CV_16S, kernel_N)
- edge4_img_N = cv2.filter2D(lap_filter_N, cv2.CV_16S, lap4_filter)
- edge4_img_N = cv2.convertScaleAbs(edge4_img_N)
-
- edge8_img_N = cv2.filter2D(lap_filter_N, cv2.CV_16S, lap8_filter)
- edge8_img_N = cv2.convertScaleAbs(edge8_img_N)
- return (Emboss_img,Motion_img,different_img,Sobel_img,Prewitt_img,edge4_img_P,edge8_img_P,edge4_img_N,edge8_img_N)
-
-
-
-
- def show(Filter_imgs):
- titles = [u'原图', u'Laplacian算子',\
- u'Emboss滤波',u'Motion滤波',
- u'diff(差分)滤波',u'Sobel滤波',u'Prewitt滤波',
- u'Lap4算子-kernel_P', u'Lap8算子-kernel_P',
- u'Lap4算子-kernel_N', u'Lap8算子-kernel_N']
-
- plt.rcParams['font.sans-serif'] = ['SimHei']
- plt.figure(figsize=(12, 8))
- for i in range(len(titles)):
- plt.subplot(3, 4, i + 1)
- plt.imshow(Filter_imgs[i])
- plt.title(titles[i])
- plt.xticks([]), plt.yticks([])
- plt.show()
-
-
- if __name__ == '__main__':
- img = cv2.imread('yinying3.png')
- img_raw = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
- gray_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
-
- LoG_img = log_filter(gray_img)
- Filter_imgs = [img_raw,LoG_img]
- Filter_imgs.extend(filter_imgs(gray_img))
- show(Filter_imgs)
Pytorch 实现sobel算子的卷积操作_洪流之源的博客-CSDN博客_卷积实现sobel
图像处理之高通滤波及低通滤波_ReWz的博客-CSDN博客_低通滤波和高通滤波对图像的影响
数字图像处理——图像梯度和空间滤波 - 知乎 (zhihu.com)
OpenCV—Python 图像滤波(均值、中值、高斯、高斯双边、高通等滤波)_SongpingWang的博客-CSDN博客
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