Android Bitmap转Base64后Python解码存PNG失败求助

Android端将Bitmap编码为Base64并写入hash.txt文件，Python中直接复制Base64字符串到变量可正常解码保存为PNG，但通过file.read()读取文件内容后解码失败。已尝试补充Base64 padding（添加==）、移除换行符等操作，问题仍存在。

import android.app.Activity;
import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.provider.MediaStore;
import android.util.Base64;

Bitmap imageBitmap = (Bitmap) extras.get("data");
String encodedString = bitMapToBase64(imageBitmap);
AfterPictureBase64(encodedString);

import base64
from PIL import Image
from io import BytesIO

def decode_base64_to_bitmap_and_save(base64_string, output_file_path):
    try:
        # Decode the base64 string to bytes
        decoded_bytes = base64.b64decode(base64_string)

        # Create a BytesIO stream from the decoded bytes
        byte_stream = BytesIO(decoded_bytes)

        # Open the image using Pillow (PIL)
        decoded_bitmap = Image.open(byte_stream)

        # Save the decoded bitmap as a PNG file
        decoded_bitmap.save(output_file_path, "PNG")

        return True  # Successful save
    except Exception as e:
        print(f"Error: {e}")
        return False  # Saving failed

# Example usage:
file_path = "hash.txt"
with open(file_path, "r") as file:
    base64_string = file.read()

output_file_path = "output.png"

if decode_base64_to_bitmap_and_save(base64_string, output_file_path):
    print(f"Image saved as {output_file_path}")
else:
    print("Failed to decode and save the image.")

• 统一编码与清理字符串：
  Python读取文件时指定UTF-8编码，并移除首尾空白、非法字符，自动补充正确的padding：

  import re
  import base64
  from PIL import Image
  from io import BytesIO
  
  def decode_base64_to_bitmap_and_save(base64_string, output_file_path):
      try:
          # 清理非法字符，只保留Base64合法字符
          base64_string = re.sub(r'[^A-Za-z0-9+/=]', '', base64_string)
          # 自动补充padding
          padding = len(base64_string) % 4
          if padding != 0:
              base64_string += '=' * (4 - padding)
          
          decoded_bytes = base64.b64decode(base64_string)
          byte_stream = BytesIO(decoded_bytes)
          decoded_bitmap = Image.open(byte_stream)
          decoded_bitmap.save(output_file_path, "PNG")
          return True
      except Exception as e:
          print(f"Error: {e}")
          return False
  
  # 修改读取逻辑
  file_path = "hash.txt"
  with open(file_path, "r", encoding="utf-8") as file:
      base64_string = file.read().strip()
  
  output_file_path = "output.png"
  if decode_base64_to_bitmap_and_save(base64_string, output_file_path):
      print(f"Image saved as {output_file_path}")
  else:
      print("Failed to decode and save the image.")
  

• 修正Android端编码逻辑：
  确保bitMapToBase64方法无多余字符输出，使用Base64.NO_WRAP避免自动添加换行：

  private String bitMapToBase64(Bitmap bitmap) {
      ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
      bitmap.compress(Bitmap.CompressFormat.PNG, 100, byteArrayOutputStream);
      byte[] byteArray = byteArrayOutputStream.toByteArray();
      // 用NO_WRAP避免编码时插入换行符
      return Base64.encodeToString(byteArray, Base64.NO_WRAP);
  }
  

内容的提问来源于stack exchange，提问作者Ian