使用Python Image库保存文件时更改DPI

Question

我使用的是python库Image，无法将图片保存在更高的DPI中。

以下是代码：

import Image as im 
    import ImageFilter as imf 
    frame = im.new('RGBA', (300,300), "white") 
    c = frame.load() 
    for m in range(0,pylab.size(mutInts)): 
        #Convert the mutation into a colour
        r = make_r(mutInts[m])
        g = make_g(mutInts[m])
        b = make_b(mutInts[m])
        if (type(r) != int):
            r = 150
            print "error: returned r was not an int.. subbing in 150"
        if (type(g) != int):
            g = 150
            print "error: returned g was not an int.. subbing in 150"
        if (type(b) != int):
            b = 150
            print "error: returned b was not an int.. subbing in 150"
        c[int(i[m]),300-int(j[m])] = (r, g, b, 255)

    print frame.size 
    frame = frame.resize([int(3*s) for s in frame.size]) 
    frame = frame.filter(imf.SMOOTH_MORE) 
    picturefilename = newLocation + 'picture_' + filename[:-4] + '.jpg'
    #Save the picture 
    frame.save(picturefilename)

我认为frame.save可能有一个我可以使用的dpi选项，但我还没找到任何东西。任何帮助控制尺寸和DPI赞赏！