无扩展名图片可被OpenCV读取的原因探究

Great question! Let me break this down for you in simple terms:

• File extensions are just labels, not the actual file identity
  Operating systems use extensions like .jpg or .png to guess a file's type, but the real format information lives inside the file itself. Every image format has a unique "file signature" — a specific sequence of bytes at the start of the file — that tells programs what kind of data they’re dealing with. For example:

  • JPEG files start with the byte sequence FF D8 FF
  • PNG files start with 89 50 4E 47 0D 0A 1A 0A
  • BMP files kick off with 42 4D

• OpenCV looks at the file content, not the filename
  When you use functions like cv2.imread(), OpenCV doesn’t waste time checking the filename extension. Instead, it reads the first few bytes of the saved file, matches that sequence against its database of known image signatures, and uses the right decoder to parse the rest of the data. Since you saved the full, unmodified binary content of the image (via f.write(request.content)), all those critical signature bytes are intact. That’s why OpenCV can correctly identify the format and load the image without any issues.

• A quick heads-up about other tools
  While OpenCV is smart enough to ignore extensions, some simpler programs do rely on them to decide how to open a file. So you might run into trouble if you try to open your extension-less image with a basic desktop viewer. But for OpenCV’s workflow, as long as the binary data is complete, it doesn’t care what you named the file.

内容的提问来源于stack exchange，提问作者ganLover