图像转换 - 无法将RGBA模式写入JPEG

Question

我想在项目上传之前调整并降低图像的大小和质量。 这是我尝试过的方法：

def save(self):
    im = Image.open(self.image)
    output = BytesIO()
    im = im.resize(240, 240)
    im.save(output, format='JPEG', quality=95)
    output.seek(0)
    self.image = InMemoryUploadedFile(output, 'ImageField', "%s.jpg" % self.image.name.split('.')[0], 'image/jpeg', sys.getsizeof(output), None)
    super(Model, self).save()

如果我上传jpg图像，它可以正常工作，但如果我上传png或任何其他类型的图像，则无法工作，会出现错误，如cannot write mode RGBA as JPEG和cannot write mode P as JPEG等。

我们该如何解决这个问题呢？谢谢！

- user9203538

---

@Teemu先生，每当我上传jpg图像时，它都可以正常工作，但如果我上传其他类型的图像，则会引发错误。我们如何将图像类型更改为jpg，以便它可以正常工作。我是新来的，所以我不小心添加了JavaScript和PHP，我已经将它们删除 :) - user9203538

我不熟悉Python，但是“无法将RGBA模式写入JPEG”听起来只有在jpg格式下才有道理..? - Teemu

@Teemu 先生，当我上传一个 png 图像时出现了这个错误。 - user9203538

Answer 1

如果你的图像模式是 "P" 或 "RGBA"，并且你想将它转换为jpeg格式，那么你需要先将 image.mode 转换，因为之前的模式不支持jpeg格式。

if im.mode in ("RGBA", "P"):
    im = im.convert("RGB")

https://github.com/python-pillow/Pillow/issues/2609

- timop

Answer 2

摘要timop和2：

• backgroud

  • JPG not support alpha = transparency
  • RGBA, P has alpha = transparency
    • RGBA= Red Green Blue Alpha

• result

  • cannot write mode RGBA as JPEG
  • cannot write mode P as JPEG

• solution

  • before save to JPG, discard alpha = transparency
    • such as: convert Image to RGB
  • then save to JPG

• your code

  if im.mode == "JPEG":
      im.save(output, format='JPEG', quality=95)
  elif im.mode in ["RGBA", "P"]:
      im = im.convert("RGB")
      im.save(output, format='JPEG', quality=95)
  

• More for you:

关于 调整大小并降低图像质量，我已经实现了一个函数供您（和其他人）参考：

from PIL import Image, ImageDraw
cfgDefaultImageResample = Image.BICUBIC # Image.LANCZOS

def resizeImage(inputImage,
                newSize,
                resample=cfgDefaultImageResample,
                outputFormat=None,
                outputImageFile=None
                ):
    """
        resize input image
        resize normally means become smaller, reduce size
    :param inputImage: image file object(fp) / filename / binary bytes
    :param newSize: (width, height)
    :param resample: PIL.Image.NEAREST, PIL.Image.BILINEAR, PIL.Image.BICUBIC, or PIL.Image.LANCZOS
        https://pillow.readthedocs.io/en/stable/reference/Image.html#PIL.Image.Image.thumbnail
    :param outputFormat: PNG/JPEG/BMP/GIF/TIFF/WebP/..., more refer:
        https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html
        if input image is filename with suffix, can omit this -> will infer from filename suffix
    :param outputImageFile: output image file filename
    :return:
        input image file filename: output resized image to outputImageFile
        input image binary bytes: resized image binary bytes
    """
    openableImage = None
    if isinstance(inputImage, str):
        openableImage = inputImage
    elif CommonUtils.isFileObject(inputImage):
        openableImage = inputImage
    elif isinstance(inputImage, bytes):
        inputImageLen = len(inputImage)
        openableImage = io.BytesIO(inputImage)

    if openableImage:
        imageFile = Image.open(openableImage)
    elif isinstance(inputImage, Image.Image):
        imageFile = inputImage
    # <PIL.PngImagePlugin.PngImageFile image mode=RGBA size=3543x3543 at 0x1065F7A20>
    imageFile.thumbnail(newSize, resample)
    if outputImageFile:
        # save to file
        imageFile.save(outputImageFile)
        imageFile.close()
    else:
        # save and return binary byte
        imageOutput = io.BytesIO()
        # imageFile.save(imageOutput)
        outputImageFormat = None
        if outputFormat:
            outputImageFormat = outputFormat
        elif imageFile.format:
            outputImageFormat = imageFile.format
        imageFile.save(imageOutput, outputImageFormat)
        imageFile.close()
        compressedImageBytes = imageOutput.getvalue()
        compressedImageLen = len(compressedImageBytes)
        compressRatio = float(compressedImageLen)/float(inputImageLen)
        print("%s -> %s, resize ratio: %d%%" % (inputImageLen, compressedImageLen, int(compressRatio * 100)))
        return compressedImageBytes

最新的代码可以在这里找到：

https://github.com/crifan/crifanLibPython/blob/master/crifanLib/crifanMultimedia.py

- crifan