使用pillow的thumbnail生成缩略图时，会保持原图的宽高比；使用的opencv的resize则不会

具体代码如下：

#!/usr/bin/env python
import re
import sys
from enum import Enum
from io import BytesIO
from pathlib import Path
from typing import Annotated, Literal, Optional, Tuple, Union# pip install python-multipart fastapi-cdn-host fastapi uvicorn pillow opencv-python
import cv2  # type:ignore[import-untyped]
import fastapi_cdn_host
import numpy as np
import uvicorn
from fastapi import FastAPI, File, HTTPException, Query
from fastapi.responses import RedirectResponse, Response
from PIL import ImageImageSizeType = Annotated[Tuple[int, int], "图片尺寸（宽，高），如：(1080, 720)"]class Picture:default_size = (351, 190)@staticmethoddef generate_thumbnail_pil(img_bytes: bytes, size, fmt: Literal["JPEG", "PNG"], *, verbose=False) -> bytes:with Image.open(BytesIO(img_bytes)) as image:origin_size = image.sizeimage.thumbnail(size)if verbose:print(f"pil[target_{size=}]: {origin_size} -> {image.size}")bio = BytesIO()if fmt == "JPEG":image = image.convert("RGB")image.save(bio, format=fmt)return bio.getvalue()@staticmethoddef generate_thumbnail_opencv(img_bytes: bytes, size, fmt: Literal[".jpeg", ".png"], *, verbose=False) -> bytes:img = cv2.imdecode(np.frombuffer(img_bytes, dtype=np.uint8), cv2.IMREAD_COLOR)resized = cv2.resize(img, size)if verbose:origin_size, converted_size = img.shape[:2][::-1], resized.shape[:2][::-1]print(f"opencv[target_{size=}]: {origin_size} -> {converted_size}")_, img_encode = cv2.imencode(fmt, resized)return img_encode.tobytes()@classmethoddef thumbnail(cls,img: Union[bytes, BytesIO, str, Path],size: Optional[ImageSizeType] = None,keep_scale=False,fmt: Optional[str] = None,*,verbose=False,) -> bytes:"""生成缩略图:param img: 图片二进制或路径:param size: 缩略图的宽、高, 如果为None，则使用类的default_size:param keep_scale: 是否保持宽高比:param fmt: 缩略图格式(jpg或png):param verbose: 调试用参数，是否打印生成的缩略图尺寸Usage::>>> p = Path('a.jpg')>>> thumb = Picture.thumbnail(p.read_bytes(), fmt=p.suffix)>>> isinstance(thumb, bytes)True"""if size is None:size = cls.default_sizeif fmt is None:if isinstance(img, (str, Path)) and str(img).lower().endswith(".png"):fmt = "png"else:fmt = fmt.strip(".").lower()assert fmt in ("jpg", "jpeg", "png"), "Invalid `fmt`: only support png/jpg"if isinstance(img, BytesIO):img = img.getvalue()elif isinstance(img, (str, Path)):img = Path(img).read_bytes()if keep_scale:fmt1: Literal["PNG", "JPEG"] = "PNG" if fmt == "png" else "JPEG"return cls.generate_thumbnail_pil(img, size, fmt=fmt1, verbose=verbose)else:fmt2: Literal[".png", ".jpeg"] = ".png" if fmt == "png" else ".jpeg"return cls.generate_thumbnail_opencv(img, size, fmt=fmt2, verbose=verbose)class ValidationError(HTTPException):def __init__(self, detail: str, status_code=400) -> None:super().__init__(status_code=status_code, detail=detail)app = FastAPI(title="Thumbnail Generator")
fastapi_cdn_host.monkey_patch_for_docs_ui(app)@app.get("/", include_in_schema=False)
async def to_docs():return RedirectResponse("/docs")class FmtEnum(str, Enum):jpg = "JPEG"png = "PNG"class ImageResponse(Response):media_type: Literal["image/jpeg", "image/png"] = "image/jpeg"def __init__(self, content: bytes, status_code=200, **kw) -> None:super().__init__(content=content, status_code=status_code, **kw)@classmethoddef docs_schema(cls) -> dict:example = b"\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x06f..."return {"content": {"image/png": {"example": str(example)},"image/jpeg": {"example": str(example).replace("PNG", "JFIF")},},"description": "返回二进制JPEG/PNG图片.",}class JpegResponse(ImageResponse):media_type = "image/jpeg"class PngResponse(ImageResponse):media_type = "image/png"@app.post("/thumbnail",response_class=ImageResponse,responses={200: ImageResponse.docs_schema()},
)
async def generate_thumbnail(size: Annotated[Union[str, None],Query(max_length=50,description="缩略图尺寸，默认为: {}x{}".format(*Picture.default_size),),] = None,fmt: Annotated[FmtEnum, Query(description="缩略图格式")] = FmtEnum.jpg,uploaded_image: bytes = File(),
) -> ImageResponse:width, height = Picture.default_sizeif size:try:width, height = map(int, re.findall(r"\d+", size))except (ValueError, TypeError):raise ValidationError(f"Invalid size type! Expected: {width}x{height}, Example: 1080x720")img_bytes = Picture.thumbnail(uploaded_image, size=(width, height), fmt=fmt)return PngResponse(img_bytes) if fmt == FmtEnum.png else JpegResponse(img_bytes)def runserver() -> None:port = int(sys.argv[1]) if sys.argv[1:] and sys.argv[1].isdigit() else 8000uvicorn.run(f"{Path(__file__).stem}:app", port=port, reload=True)if __name__ == "__main__":runserver()

效果如下：