iPhone高速参考：从一个图片截取部分区域生成新的小图

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?? ?UIImage *image = [[UIImage alloc] initWithData:data];//大图

?? ?CGRect imageRect = CGRectMake(0.0,?0.0, image.size.width, image.size.height);

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?? ?CGSize itemSize = CGSizeMake(w,h);

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?? ?UIGraphicsBeginImageContext(itemSize);

?? ?[image drawInRect:imageRect];

?? ?UIImage *smallimage?= UIGraphicsGetImageFromCurrentImageContext();

?? ?UIGraphicsEndImageContext();