IOS 改变图片尺寸和大小方法

一、改变size 

- (UIImage *)image:(UIImage*)image byScalingToSize:(CGSize)targetSize {
    UIImage *sourceImage = image;
    UIImage *newImage = nil;

    UIGraphicsBeginImageContext(targetSize);

    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = CGPointZero;
    thumbnailRect.size.width  = targetSize.width;
    thumbnailRect.size.height = targetSize.height;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage ;
}

二、改变字节(多用于上传至服务器时) 

UIKIT_EXTERN NSData *UIImagePNGRepresentation(UIImage *image);                               
UIKIT_EXTERN NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);