[英]Segmenting letters in a Captcha image
I've written this algorithm in Python for reading CAPTCHAs using scikit-image:我已经用 Python 编写了这个算法,用于使用 scikit-image 读取 CAPTCHA:
from skimage.color import rgb2gray
from skimage import io
def process(self, image):
"""
Processes a CAPTCHA by removing noise
Args:
image (str): The file path of the image to process
"""
input = io.imread(image)
histogram = {}
for x in range(input.shape[0]):
for y in range(input.shape[1]):
pixel = input[x, y]
hex = '%02x%02x%02x' % (pixel[0], pixel[1], pixel[2])
if hex in histogram:
histogram[hex] += 1
else:
histogram[hex] = 1
histogram = sorted(histogram, key = histogram.get, reverse=True)
threshold = len(histogram) * 0.015
for x in range(input.shape[0]):
for y in range(input.shape[1]):
pixel = input[x, y]
hex = '%02x%02x%02x' % (pixel[0], pixel[1], pixel[2])
index = histogram.index(hex)
if index < 3 or index > threshold:
input[x, y] = [255, 255, 255, 255]
input = rgb2gray(~input)
io.imsave(image, input)
Before:前:
After:后:
It works fairly well and I get decent results after running it through Google's Tesseract OCR, but I want to make it better.它运行得相当好,在通过 Google 的 Tesseract OCR 运行后我得到了不错的结果,但我想让它变得更好。 I think that straightening the letters would yield a much better result.我认为拉直字母会产生更好的结果。 My question is how do I do that?我的问题是我该怎么做?
I understand I need to box the letters somehow, like so:我知道我需要以某种方式将字母装箱,如下所示:
Then, for each character, rotate it some number of degrees based on a vertical or horizontal line.然后,对于每个字符,根据垂直或水平线将其旋转一定度数。
My initial thought was to identify the center of a character (possibly by finding clusters of most used colors in the histogram) and then expanding a box until it found black, but again, I'm not so sure how to go about doing that.我最初的想法是确定一个字符的中心(可能通过在直方图中找到最常用颜色的簇)然后扩展一个框直到它找到黑色,但同样,我不太确定如何去做。
What are some common practices used in image segmentation to achieve this result?图像分割中使用哪些常见做法来实现此结果?
Edit:编辑:
In the end, further refining the color filters and limiting Tesseract to only characters yielded a nearly 100% accurate result without any deskewing.最后,进一步细化滤色器并将 Tesseract 限制为仅字符,产生了近 100% 准确的结果,没有任何纠偏。
Operation you want to do is technically in computer vision known as deskewing of the objects, for this you have to apply a geometric transformation on the objects, i have a snippet of the code to do apply deskewing on objects (binary).你想要做的操作在技术上是在计算机视觉中被称为对象的纠偏,为此你必须对对象应用几何变换,我有一段代码来对对象(二进制)应用纠偏。 here is the code(uses opencv library):这是代码(使用opencv库):
def deskew(image, width):
(h, w) = image.shape[:2]
moments = cv2.moments(image)
skew = moments["mu11"] / moments["mu02"]
M = np.float32([[1, skew, -0.5 * w * skew],[0, 1, 0]])
image = cv2.warpAffine(image, M, (w, h), flags = cv2.WARP_INVERSE_MAP | cv2.INTER_LINEAR)
return image
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