Python pillow模块出现cannot write mode RGBA as JPEG问题的解决方法

Posted 2021-08-18 但老师

背景

最近在解决一个问题:如何自动截取Excel里面的范围为图片并发送.最后使用pywin32模块解决了,但是在发送的时候,个别部署电脑会出现一些问题,就是下面这种报错

cannot write mode RGBA as JPEG

后来发现有些电脑在使用VBA的CopyPicture方法会默认为PNG格式,有些默认是JPG格式,奇奇怪怪的

问题

出现问题的是下面这一段,为了更好理解,我将上下文放了出来

img = ImageGrab.grabclipboard()
imgpath = os.path.join(os.path.dirname(__file__),'{imgname}.{fmt}'.format(imgname=time.strftime('%Y%m%d%H%M%S'),fmt=fmt))
img.save(imgpath) # 这一句有报错

报错完整信息如下

Traceback (most recent call last):
  File "C:\\Users\\Administrator\\AppData\\Local\\Programs\\Python\\Python39\\lib\\site-packages\\PIL\\JpegImagePlugin.py", line 611, in _save
    rawmode = RAWMODE[im.mode]
KeyError: 'RGBA'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "D:\\onedrive\\doc\\for_share\\Python_eco\\python\\work_wechat_amiba.py", line 22, in <module>
    amiba()
  File "D:\\onedrive\\doc\\for_share\\Python_eco\\python\\work_wechat_amiba.py", line 14, in amiba
    img = excel.savePic(['post'],'jpg')
  File "D:\\onedrive\\doc\\for_share\\Python_eco\\python\\Udfs\\cls_excel.py", line 80, in savePic
    img.save(self._picPath)
  File "C:\\Users\\Administrator\\AppData\\Local\\Programs\\Python\\Python39\\lib\\site-packages\\PIL\\Image.py", line 2151, in save
    save_handler(self, fp, filename)
  File "C:\\Users\\Administrator\\AppData\\Local\\Programs\\Python\\Python39\\lib\\site-packages\\PIL\\JpegImagePlugin.py", line 613, in _save
    raise OSError(f"cannot write mode {im.mode} as JPEG") from e
OSError: cannot write mode RGBA as JPEG

方案

解决方案也是非常简单,加一句转换就可以了

img = ImageGrab.grabclipboard()
imgpath = os.path.join(os.path.dirname(__file__),'{imgname}.{fmt}'.format(imgname=time.strftime('%Y%m%d%H%M%S'),fmt=fmt))
img.convert('RGB')	# 这一句
img.save(imgpath)

结论

1. 如果保存格式为jpg,最好加上这句转换
2. 如果保存格式为png,可以不用这句

如果有一个格式变量,那最终加进去的如下

if fmt == 'jpg':
	img.convert('RGB')