86 lines
3.0 KiB
Python
86 lines
3.0 KiB
Python
import os
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import pathlib
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import subprocess
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from typing import Union
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import matplotlib
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import matplotlib.pyplot as plt
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class Week1:
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def __init__(self):
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# 避免覆盖内置名 list
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self.qualities = [2, 7, 12, 17, 22, 27, 31]
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def _ffmpeg_path(self) -> pathlib.Path:
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"""
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返回项目 bin 目录下 ffmpeg 的可执行路径。
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Week1/Week1.py 位于项目的 Week1 目录内，bin 与 Week1 处于同级。
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"""
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here = pathlib.Path(__file__).resolve()
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project_root = here.parent.parent # <project_root>/Week1/Week1.py -> <project_root>
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bin_dir = project_root / "bin"
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exe_name = "ffmpeg.exe" if os.name == "nt" else "ffmpeg"
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ffmpeg = bin_dir / exe_name
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if not ffmpeg.exists():
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raise FileNotFoundError(f"未找到 ffmpeg 可执行文件: {ffmpeg}")
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return ffmpeg
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def compress(self, image_src: Union[str, pathlib.Path]):
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"""
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使用不同 q:v 质量参数将 PNG 转为 JPEG。
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输出文件与输入文件位于同目录，命名为 <原名>_<q>.jpg
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"""
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image_path = pathlib.Path(image_src).resolve()
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if not image_path.exists():
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raise FileNotFoundError(f"输入图像不存在: {image_path}")
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ffmpeg = self._ffmpeg_path()
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stem = image_path.stem
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parent = image_path.parent
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for q in self.qualities:
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out_path = parent / f"{stem}_{q}.jpg"
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# -y 覆盖已存在文件；参数以列表方式传入
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cmd = [
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str(ffmpeg),
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"-y",
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"-i", str(image_path),
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"-q:v", str(q),
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str(out_path),
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]
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# 失败时抛异常，便于定位问题
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subprocess.run(cmd, check=True)
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def render(self, image_src: Union[str, pathlib.Path]):
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"""
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读取生成的 JPEG 文件大小，并绘制质量(q) vs 文件大小(bytes) 的折线图。
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"""
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image_path = pathlib.Path(image_src).resolve()
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stem = image_path.stem
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parent = image_path.parent
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sizes = []
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qualities = []
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for q in self.qualities:
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jpg_path = parent / f"{stem}_{q}.jpg"
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if not jpg_path.exists():
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# 若缺失，给出清晰异常，提示先运行 compress
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raise FileNotFoundError(f"缺少压缩输出文件，请先运行 compress: {jpg_path}")
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qualities.append(q)
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sizes.append(os.path.getsize(jpg_path)/8)
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# 使用 pyplot 正确保存图像
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plt.figure(figsize=(6, 4))
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plt.plot(qualities, sizes, marker="o")
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plt.xlabel("JPEG quality (q:v)")
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plt.ylabel("File size (Kbytes)")
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plt.title("Quality vs File Size")
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plt.grid(True)
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project_root = pathlib.Path(__file__).resolve().parent.parent
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out_png = project_root / "data" / "render.png"
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out_png.parent.mkdir(parents=True, exist_ok=True)
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plt.tight_layout()
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plt.savefig(str(out_png))
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plt.close() |