ReportLab Python:透明背景变黑，画质不佳

from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import A4
from reportlab.lib.colors import Color

def create_pdf(filename):
    c = canvas.Canvas(filename, pagesize=A4)
    width, height = A4

    # 设置背景颜色为白色
    c.setFillColor(Color(1, 1, 1))
    c.rect(0, 0, width, height, fill=True, stroke=False)

    # 绘制带有透明度的图形
    c.setFillColorRGB(0.2, 0.5, 0.8, alpha=0.5)
    c.rect(50, 50, 200, 100, fill=True, stroke=False)

    c.save()

create_pdf("example.pdf")

from reportlab.platypus import Image
from reportlab.lib.pagesizes import A4

def add_high_quality_image(canvas, image_path, x, y):
    img = Image(image_path, width=200, height=200)
    img.drawOn(canvas, x, y)

def create_pdf_with_image(filename):
    c = canvas.Canvas(filename, pagesize=A4)
    width, height = A4

    # 添加高分辨率图像
    add_high_quality_image(c, "high_res_image.png", 50, 50)

    c.save()

create_pdf_with_image("example_with_image.pdf")