iOS如何将图像的一部分绘制到特定的rect？

I want to crop a 200*200 image, the cropped part is (x=10,y=10,w=50,h=50). and drawing this part to new 500*500 image, the new rect is (x=30,y=30,w=50, h=50), how to do it? I want to crop a 200*200 image, the cropped par