Python使用PIL库实现高质量图片缩放功能

from PIL import Image

img = Image.open("大图.jpg")

# ❌ 默认（质量一般）
small = img.resize((800, 600))

# ✅ 高质量（推荐）
small = img.resize((800, 600), resample=Image.LANCZOS)

# 旧版本（< 10.0）
img.resize((800, 600), resample=Image.LANCZOS)

# 新版本（>= 10.0）
img.resize((800, 600), resample=Image.Resampling.LANCZOS)

small.save("out.jpg", quality=95, subsampling=0)

from PIL import Image

img = Image.open("大图.jpg")

# 1. 缩放（LANCZOS 保证缩放质量）
small = img.resize((800, 600), resample=Image.LANCZOS)

# 2. 保存（quality=95 保证保存质量）
small.save("小图.jpg", quality=95, subsampling=0, optimize=True)

# 放大 2 倍，依然用 LANCZOS
big = img.resize((4000, 3000), resample=Image.LANCZOS)

from PIL import Image

def resize_exact_size(input_path, output_path, new_size):
    """
    将图片精确缩放到指定尺寸 (宽度, 高度)
    :param input_path: 输入图片路径
    :param output_path: 输出图片路径
    :param new_size: 新的尺寸 (宽度, 高度)
    """
    try:
        with Image.open(input_path) as img:
            # Image.LANCZOS 是最高质量的滤镜
            resized_img = img.resize(new_size, Image.LANCZOS)
            resized_img.save(output_path)
            print(f"图片已成功保存至 {output_path}")
    except Exception as e:
        print(f"处理图片时出错: {e}")

# 使用示例
resize_exact_size("input.jpg", "output_800x600.jpg", (800, 600))

from PIL import Image

def resize_fixed_width(input_path, output_path, target_width):
    """
    固定宽度，高度按原图比例自动缩放
    :param input_path: 输入图片路径
    :param output_path: 输出图片路径
    :param target_width: 目标宽度
    """
    try:
        with Image.open(input_path) as img:
            original_width, original_height = img.size
            # 按比例计算新的高度
            target_height = int(original_height * (target_width / original_width))
            new_size = (target_width, target_height)
            resized_img = img.resize(new_size, Image.LANCZOS)
            resized_img.save(output_path)
            print(f"图片已保存，新尺寸为 {new_size}")
    except Exception as e:
        print(f"处理图片时出错: {e}")

# 示例：固定宽度为 800 像素
resize_fixed_width("input.jpg", "output_width800.jpg", 800)

from PIL import Image

def create_thumbnail(input_path, output_path, max_size):
    """
    创建缩略图，确保其尺寸不超过 (max_width, max_height)
    :param input_path: 输入图片路径
    :param output_path: 输出图片路径
    :param max_size: 最大尺寸 (最大宽度, 最大高度)
    """
    try:
        with Image.open(input_path) as img:
            # thumbnail() 会直接修改 img 对象本身
            img.thumbnail(max_size, Image.LANCZOS)
            img.save(output_path)
            print(f"缩略图已保存，实际尺寸为 {img.size}")
    except Exception as e:
        print(f"处理图片时出错: {e}")

# 示例：创建一个最大边长为 400x400 的缩略图
create_thumbnail("input.jpg", "thumbnail_400x400.jpg", (400, 400))

from PIL import Image
def resize_image(input_path, output_path, new_size, 
                 keep_aspect=False, use_thumbnail=False, quality=95):
    """
    通用的图片缩放函数
    :param input_path: 输入图片路径
    :param output_path: 输出图片路径
    :param new_size: 目标尺寸，可为 (width, height) 或 (max_width, max_height)
    :param keep_aspect: 是否保持纵横比
    :param use_thumbnail: 是否使用 thumbnail 方法 (仅缩小)
    :param quality: 输出图片的质量 (1-100)，用于 JPEG
    """
    try:
        with Image.open(input_path) as img:
            # RGBA 转 RGB，以防保存为 JPEG 时出错
            if img.mode == 'RGBA' and output_path.lower().endswith('.jpg'):
                img = img.convert('RGB')
            if use_thumbnail:
                # 使用 thumbnail，它会自动保持纵横比
                img.thumbnail(new_size, Image.LANCZOS)
                img.save(output_path, quality=quality)
            elif keep_aspect:
                # 固定宽度或高度，计算另一维
                original_width, original_height = img.size
                target_width, target_height = new_size
                # 判断是基于宽还是高进行缩放
                if target_width:
                    new_h = int(original_height * (target_width / original_width))
                    final_size = (target_width, new_h)
                elif target_height:
                    new_w = int(original_width * (target_height / original_height))
                    final_size = (new_w, target_height)
                else:
                    final_size = new_size
                resized_img = img.resize(final_size, Image.LANCZOS)
                resized_img.save(output_path, quality=quality)
            else:
                # 精确缩放
                resized_img = img.resize(new_size, Image.LANCZOS)
                resized_img.save(output_path, quality=quality)
            print(f"处理完成：{output_path}")
    except Exception as e:
        print(f"处理失败：{e}")
# 示例
# 1. 精确缩放到 800x600
# resize_image("input.jpg", "output_exact.jpg", (800, 600), keep_aspect=False)
# 2. 固定宽度 800，高度按比例
# resize_image("input.jpg", "output_fixed_width.jpg", (800, None), keep_aspect=True)
# 3. 生成一个最大边长为 400x400 的缩略图
# resize_image("input.jpg", "output_thumbnail.jpg", (400, 400), use_thumbnail=True)