[英]How to keep Only Black color text in the image using OpenCV Python?
一種可能的解決方案包括將圖像轉換為CMYK
顏色空間並提取K
(Key - black)通道,對其進行閾值化並應用一些形態學來清理二進制圖像。
OpenCV 沒有實現從BGR
到CMYK
的轉換,所以我們必須手動計算K
通道。 代碼如下所示:
# Imports
import cv2
import numpy as np
# Read image
imagePath = "D://opencvImages//"
inputImage = cv2.imread(imagePath + "A6RXi.png")
# Conversion to CMYK (just the K channel):
# Convert to float and divide by 255:
imgFloat = inputImage.astype(np.float) / 255.
# Calculate channel K:
kChannel = 1 - np.max(imgFloat, axis=2)
# Convert back to uint 8:
kChannel = (255 * kChannel).astype(np.uint8)
這是 K(黑色)通道:
現在,使用固定值對圖像進行閾值處理。 在這種情況下,我將閾值設置為190
:
# Threshold image:
binaryThresh = 190
_, binaryImage = cv2.threshold(kChannel, binaryThresh, 255, cv2.THRESH_BINARY)
這是二進制圖像:
這是一點噪音,但如果我們實施區域過濾器,我們可以去除較小的斑點。 function 在本文末尾定義。 讓我們應用最小值為100
的過濾器。 所有小於此的 blob 都將被刪除:
# Filter small blobs:
minArea = 100
binaryImage = areaFilter(minArea, binaryImage)
這是過濾后的圖像:
涼爽的。 讓我們用一個關閉過濾器來改善 blob 的形態:
# Use a little bit of morphology to clean the mask:
# Set kernel (structuring element) size:
kernelSize = 3
# Set morph operation iterations:
opIterations = 2
# Get the structuring element:
morphKernel = cv2.getStructuringElement(cv2.MORPH_RECT, (kernelSize, kernelSize))
# Perform closing:
binaryImage = cv2.morphologyEx(binaryImage, cv2.MORPH_CLOSE, morphKernel, None, None, opIterations, cv2.BORDER_REFLECT101)
cv2.imshow("binaryImage [closed]", binaryImage)
cv2.waitKey(0)
這是最終結果:
這就是areaFilter
function。 它接收一個最小區域和一個二值圖像,它返回沒有小斑點的圖像:
def areaFilter(minArea, inputImage):
# Perform an area filter on the binary blobs:
componentsNumber, labeledImage, componentStats, componentCentroids = \
cv2.connectedComponentsWithStats(inputImage, connectivity=4)
# Get the indices/labels of the remaining components based on the area stat
# (skip the background component at index 0)
remainingComponentLabels = [i for i in range(1, componentsNumber) if componentStats[i][4] >= minArea]
# Filter the labeled pixels based on the remaining labels,
# assign pixel intensity to 255 (uint8) for the remaining pixels
filteredImage = np.where(np.isin(labeledImage, remainingComponentLabels) == True, 255, 0).astype('uint8')
return filteredImage
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