Matplotlib: scatter nhiều biến và chú giải rõ ràng

from pathlib import Path
import json
import numpy as np
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
OUTPUT = Path(__file__).resolve().parent / "results"
OUTPUT.mkdir(exist_ok=True)
plt.rcParams.update({"font.size": 12, "axes.spines.top": False,
                     "axes.spines.right": False, "figure.facecolor": "#f3f7f6",
                     "axes.facecolor": "white", "axes.titleweight": "bold"})
FIGURE = OUTPUT / "matplotlib-scatter.png"

rng = np.random.default_rng(17)
size = rng.uniform(10, 90, 80)
contrast = rng.uniform(0.1, 0.95, 80)
error = np.clip(0.8 - size / 180 - contrast / 3 + rng.normal(0, 0.06, 80), 0, 1)
area = 25 + size * 1.8
assert size.shape == contrast.shape == error.shape == area.shape
assert np.isfinite(error).all()
print("Samples:", len(size))

fig, axes = plt.subplots(1, 2, figsize=(12, 8), layout="constrained")
points = axes[0].scatter(size, contrast, c=error, s=area, cmap="YlGn", vmin=0, vmax=1, alpha=0.8, edgecolors="#294b40", linewidths=0.4)
fig.colorbar(points, ax=axes[0], label="Simulated error")
axes[0].set(title="Size, contrast and error", xlabel="Object size (px)", ylabel="Contrast")
axes[1].scatter(size, error, s=35, color="#356a59", alpha=0.65)
axes[1].set(title="A simpler two-variable view", xlabel="Object size (px)", ylabel="Simulated error")

worst = int(np.argmax(error))
axes[1].annotate(f"Sample {worst}", (size[worst], error[worst]), xytext=(12, -25), textcoords="offset points", arrowprops={"arrowstyle": "->"})
for ax in axes:
    ax.grid(alpha=0.18)
handles = [axes[0].scatter([], [], s=25+v*1.8, color="#90ae99", label=f"Size {v} px") for v in [20, 70]]
axes[0].legend(handles=handles, fontsize=9, loc="lower left")
assert error[worst] == error.max()
fig.savefig(FIGURE, dpi=100)
plt.close(fig)
print("Saved:", FIGURE.name)

.\.venv\Scripts\python.exe matplotlib_scatter.py