from PIL import Image

def process(input_path,output_path,size=(480,640),dpi=(300,300)):
    ratio=size[0]/size[1]
    
    img0=Image.open(input_path)
    
    ratio_0=img0.size[0]/img0.size[1]
    
    if ratio<ratio_0: #如果宽度相对较大
        temp_size=(size[1]*ratio_0,size[1])
        
    elif ratio>ratio_0: #如果长度相对较大
        temp_size=(size[0],size[0]*ratio_0)
        
    else: #如果长宽比刚好相等
        img2=img0.resize(size=size)
        img2.save(output_path,dpi=dpi)
        return #保存并退出
    
    
    temp_size=[round(c) for c in  temp_size]
    img2=img0.resize(temp_size)
    
    left=round( (temp_size[0]-size[0])/2)
    top=round( (temp_size[1]-size[1])/2)
    right=left+size[0]
    bottom=top+size[1]
    
    #裁剪
    img2=img2.crop((left,top,right,bottom))
    
    img2.save(output_path,dpi=dpi)