第一个：压缩图片

当我们上传图片到服务器时，需要压缩一下图片的质量。方法如下：

/*
 *压缩图片
 */
+ (UIImage *)resizeImageWithImage:(UIImage *)image targetSize:(CGSize)targetSize;

+ (UIImage *)resizeImageWithImage:(UIImage *)image targetSize:(CGSize)targetSize
{
    CGSize size = image.size;
    CGFloat widthRatio = targetSize.width / image.size.width;
    CGFloat heightRatio = targetSize.height / image.size.height;
    CGSize newSize;
    if (widthRatio > heightRatio) newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio);
    else newSize = CGSizeMake(size.width * widthRatio, size.height * widthRatio);
    CGRect rect = CGRectMake(0, 0, newSize.width, newSize.height);
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 1.0);
    [image drawInRect:rect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

第二个，截取人脸部图片

拍摄身份证或者其他有人脸部的图片时，我们可能只需要人脸部分的头像图片。裁剪的方法如下：

/*
 *获取脸部图片
 */
+ (CGRect)adjustFaceImageWithRect:(CGRect)rect sourceImage:(UIImage *)sourceImage;

+ (CGRect)adjustFaceImageWithRect:(CGRect)rect sourceImage:(UIImage *)sourceImage
{
    CGRect faceRect;
    CGFloat widthMargin = rect.size.width/2;;
    CGFloat heightMargin = rect.size.height/2;
    faceRect.origin.x = MAX(rect.origin.x - widthMargin, 0);
    faceRect.origin.y = MAX(rect.origin.y - heightMargin - heightMargin/2, 0) + 20;
    faceRect.size.width = MIN(rect.size.width + 2*widthMargin, (CGFloat)(sourceImage.size.width - faceRect.origin.x - 1));
    faceRect.size.height = MIN(rect.size.height + 2*heightMargin + heightMargin/2, (CGFloat)(sourceImage.size.height - faceRect.origin.y - 1));
    return faceRect;
}

第三个,从一张图片上截取一部分图片

根据坐标信息，从一张大的图片上裁剪出我们需要的那一部分图片区域，具体如下：

/*
 *在一张图片上根据坐标范围裁剪图片
 */
+ (UIImage *)cutImageWithRect:(CGRect)rect image:(UIImage *)cutImage;

+ (UIImage *)cutImageWithRect:(CGRect)rect image:(UIImage *)cutImage
{
    CGImageRef cgRef = cutImage.CGImage;
    CGImageRef imageRef = CGImageCreateWithImageInRect(cgRef, rect);
    UIImage *thumbScale = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return thumbScale;
}

第四个，保存图片到本地

- (void)saveImageToPhotos:(UIImage*)savedImage
{
    UIImageWriteToSavedPhotosAlbum(savedImage, self, @selector(image:didFinishSavingWithError:contextInfo:), NULL);
}
- (void)image: (UIImage *) image didFinishSavingWithError: (NSError *) error contextInfo: (void *) contextInfo
{
    NSString *msg = nil ;
    if(error != NULL) msg = @"保存图片失败" ;
    else              msg = @"保存图片成功" ;
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"提示"
                                                    message:msg
                                                   delegate:self
                                          cancelButtonTitle:@"确定"
                                          otherButtonTitles:nil];
    [alert show];
}