转换为yuv420p格式的jpg图像

    from PIL import Image
    import numpy
    def my_open_jpg(filename):
    "open a jpg file and return a file object"
    return Image.open(filename);
    
    def my_jpg2yuv(im_jpg):
    "conver a jpg file to yuv file"
    #if(len(im_jpg.split())==4):
    #    r,g,b,a=im_jpg.split();
    #else:
    r,g,b=im_jpg.split();
    
    width,height=im_jpg.size;
    im_new=range(width*height*3/2);
    k_r = 0.299;
    k_g = 0.587
    k_b = 0.114
    r = list(r.getdata());
    g = list(g.getdata());
    b = list(b.getdata());
    for i in range(height):
        for j in range(width):