python 圖片格式轉換png轉jpg，如何利用python給圖片添加半透明水印

from PIL import Image
im = Image.open(r'd:\test2.png')
r, g, b, a = im.split()
im = Image.merge("RGB", (r, g, b))
im.save(r'D:\Python_Programming.jpg')
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# coding:utf-8

from PIL import Image, ImageDraw, ImageFont


def add_text_to_image(image, text):
    font = ImageFont.truetype('C:\Windows\Fonts\STXINGKA.TTF', 36)

    # 添加背景
    new_img = Image.new('RGBA', (image.size[0] * 3, image.size[1] * 3), (0, 0, 0, 0))
    new_img.paste(image, image.size)

    # 添加水印
    font_len = len(text)
    rgba_image = new_img.convert('RGBA')
    text_overlay = Image.new('RGBA', rgba_image.size, (255, 255, 255, 0))
    image_draw = ImageDraw.Draw(text_overlay)

    for i in range(0, rgba_image.size[0], font_len * 40 + 100):
        for j in range(0, rgba_image.size[1], 200):
            image_draw.text((i, j), text, font=font, fill=(0, 0, 0, 50))
    text_overlay = text_overlay.rotate(-45)
    image_with_text = Image.alpha_composite(rgba_image, text_overlay)

    # 裁切圖片
    image_with_text = image_with_text.crop((image.size[0], image.size[1], image.size[0] * 2, image.size[1] * 2))
    return image_with_text


if __name__ == '__main__':
    img = Image.open(r"d:\ww.jpg")
    im_after = add_text_to_image(img, u'群主是個大流X')
    im_after.save(r'd:\ww.png')

 彩色轉黑白

from PIL import Image
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.cm as cm   #cm是colormap的縮寫
image_gray=Image.open('D:/ww.png').convert("L")
data=np.array(image_gray)  #在顯示灰度圖像時array()方法將圖像轉換成Numpy的數組對象，圖片得以顯式，否則會出現錯誤
plt.imshow(data,cmap=cm.gray)# cmap:代表顏色圖譜，默認繪制為RGB(A)顏色空間。
plt.savefig("d:/ww1.png")
plt.show()

 裁剪

from PIL import Image
import matplotlib.pyplot as plt
import numpy as np
image=Image.open('D:/ww.jpg')
box=(100,100,400,400)
region=image.crop(box)
data=np.array(region)
plt.imshow(data)
plt.show()

 旋轉

from PIL import Image
import matplotlib.pyplot as plt
image=Image.open('D:/ww.png')#讀取圖像
plt.imshow(image.rotate(180))#逆時針旋轉180度
plt.show()#需要調用show()方法，不然圖像只會在內存中而不顯示出來