使用PIL在App Engine上绘制图像

我已阅读主题“App Engine、PIL 和叠加文本 https://stackoverflow.com/questions/12695480/app-engine-pil-and-overlaying-text".

下面的代码将显示损坏的图像，我应该如何纠正？

class TestImg(webapp2.RequestHandler):
    def get(self):
        text_img = Image.new('RGBA', (800,600), (0, 0, 0, 0))
        draw = ImageDraw.Draw(text_img)
        draw.text((0, 0), 'HELLO TEXT', font=ImageFont.load_default())
        self.response.headers['Content-Type'] = "image/png"
        self.response.write(draw)

根据蒂姆·霍夫曼所说，你的课程将如下所示：

import StringIO

class TestImg(webapp2.RequestHandler):
    def get(self):
        text_img = Image.new('RGBA', (800,600), (0, 0, 0, 0))
        draw = ImageDraw.Draw(text_img)
        draw.text((0, 0), 'HELLO TEXT', font=ImageFont.load_default())

        output = StringIO.StringIO()
        text_img.save(output, format="png")
        text_layer = output.getvalue()
        output.close()

        self.response.headers['Content-Type'] = 'image/png'
        self.response.write(text_layer)