Pytesseract 转换期间出现“ValueError：无法过滤调色板图像”

Question

遇到有关 Pytesseract 的以下代码的此错误代码的问题。（Python 3.6.1，Mac OSX）

从 PIL 导入 pytesseract 导入请求 从 PIL 导入图像 从 io 导入 ImageFilter 导入 StringIO, BytesIO

def process_image(url):
    image = _get_image(url)
    image.filter(ImageFilter.SHARPEN)
    return pytesseract.image_to_string(image)


def _get_image(url):
    r = requests.get(url)
    s = BytesIO(r.content)
    img = Image.open(s)
    return img

process_image("https://www.prepressure.com/images/fonts_sample_ocra_medium.png")

错误：

/usr/local/Cellar/python3/3.6.0_1/Frameworks/Python.framework/Versions/3.6/bin/python3.6 /Users/g/pyfo/reddit/ocr.py
Traceback (most recent call last):
  File "/Users/g/pyfo/reddit/ocr.py", line 20, in <module>
    process_image("https://www.prepressure.com/images/fonts_sample_ocra_medium.png")
  File "/Users/g/pyfo/reddit/ocr.py", line 10, in process_image
    image.filter(ImageFilter.SHARPEN)
  File "/usr/local/lib/python3.6/site-packages/PIL/Image.py", line 1094, in filter
    return self._new(filter.filter(self.im))
  File "/usr/local/lib/python3.6/site-packages/PIL/ImageFilter.py", line 53, in filter
    raise ValueError("cannot filter palette images")
ValueError: cannot filter palette images

Process finished with exit code 1

看起来很简单，但不起作用。任何帮助将不胜感激。

Answer 1

您拥有的图像是基于托盘的图像。您需要将其转换为完整RGB图像才能使用 PIL 过滤器。

import pytesseract 
import requests 
from PIL import Image, ImageFilter 
from io import StringIO, BytesIO

def process_image(url):
    image = _get_image(url)
    image = image.convert('RGB')
    image = image.filter(ImageFilter.SHARPEN)
    return pytesseract.image_to_string(image)


def _get_image(url):
    r = requests.get(url)
    s = BytesIO(r.content)
    img = Image.open(s)
    return img

process_image("https://www.prepressure.com/images/fonts_sample_ocra_medium.png")

您还应该注意.convert()和.filter()方法返回图像的副本，它们不会更改现有的图像对象。您需要将返回值分配给一个变量，如上面的代码所示。

注意：我没有 pytesseract，所以我无法检查process_image().