Pytesseract转换过程中出现“ValueError：无法过滤调色板图像”

Question

在Pytesseract的以下代码中遇到此错误代码的问题。从PIL进口的ImageFilter （Python的3.6.1，Mac OSX版）

进口pytesseract 导入请求 从PIL进口图片 从IO导入StringIO的，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 

似乎很简单，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的RGB图像才能使用PIL滤镜。

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") 

你也应该注意到，在.convert()和.filter()方法返回图像的副本，只要不改变现有的图像对象。您需要将返回值分配给变量，如上面的代码所示。

注：我没有pytesseract，所以我无法检查最后一行process_image()。