在开发中使用分类对原有的系统类进行方法扩展，是增强系统原有类功能的常见做法。

/**

 *  *拉伸一张图片

 *

 *  @param name 图片名字

 *  @param left 左边开始位置比例  值范围0-1

 *  @param top  上边开始位置比例  值范围0-1

 *

 *  @return 拉伸后的Image

 */

 + (UIImage *)resizedImageWithName:(NSString *)name left:(CGFloat)left top:(CGFloat)top

{

    UIImage *image = [UIImage imageNamed:name];

    return [image stretchableImageWithLeftCapWidth:image.size.width * left topCapHeight:image.size.height * top];

}

/**

 *  根据颜色和大小获取Image

 *

 *  @param color 颜色

 *  @param size  大小

 *

 */

+ (UIImage *)imageWithColor:(UIColor *)color size:(CGSize)size

{

    UIGraphicsBeginImageContextWithOptions(size, 0, [UIScreen mainScreen].scale);

    [color set];

    UIRectFill(CGRectMake(0, 0, size.width, size.height));

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return image;

}

/**

 *  根据图片和颜色返回一张加深颜色以后的图片

 */

+ (UIImage *)colorizeImage:(UIImage *)baseImage withColor:(UIColor *)theColor {

    UIGraphicsBeginImageContext(CGSizeMake(baseImage.size.width*2, baseImage.size.height*2));

    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGRect area = CGRectMake(0, 0, baseImage.size.width * 2, baseImage.size.height * 2);

    CGContextScaleCTM(ctx, 1, -1);

    CGContextTranslateCTM(ctx, 0, -area.size.height);

    CGContextSaveGState(ctx);

    CGContextClipToMask(ctx, area, baseImage.CGImage);

    [theColor set];

    CGContextFillRect(ctx, area);

    CGContextRestoreGState(ctx);

    CGContextSetBlendMode(ctx, kCGBlendModeMultiply);

    CGContextDrawImage(ctx, area, baseImage.CGImage);

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;

}

/**

 *  根据图片返回一张高斯模糊的图片

 *

 *  @param blur 模糊系数

 *

 *  @return 新的图片

 */

- (UIImage *)boxblurImageWithBlur:(CGFloat)blur {

    NSData *imageData = UIImageJPEGRepresentation(self, 1); // convert to jpeg

    UIImage* destImage = [UIImage imageWithData:imageData];

    if (blur < 0.f || blur > 1.f) {

        blur = 0.5f;

    }

    int boxSize = (int)(blur * 40);

    boxSize = boxSize - (boxSize % 2) + 1;

    CGImageRef img = destImage.CGImage;

    vImage_Buffer inBuffer, outBuffer;

    vImage_Error error;

    void *pixelBuffer;

    //create vImage_Buffer with data from CGImageRef

    CGDataProviderRef inProvider = CGImageGetDataProvider(img);

    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);

    inBuffer.width = CGImageGetWidth(img);

    inBuffer.height = CGImageGetHeight(img);

    inBuffer.rowBytes = CGImageGetBytesPerRow(img);

    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);

    //create vImage_Buffer for output

    pixelBuffer = malloc(CGImageGetBytesPerRow(img) * CGImageGetHeight(img));

    if(pixelBuffer == NULL)

        NSLog(@"No pixelbuffer");

    outBuffer.data = pixelBuffer;

    outBuffer.width = CGImageGetWidth(img);

    outBuffer.height = CGImageGetHeight(img);

    outBuffer.rowBytes = CGImageGetBytesPerRow(img);

    // Create a third buffer for intermediate processing

    void *pixelBuffer2 = malloc(CGImageGetBytesPerRow(img) * CGImageGetHeight(img));

    vImage_Buffer outBuffer2;

    outBuffer2.data = pixelBuffer2;

    outBuffer2.width = CGImageGetWidth(img);

    outBuffer2.height = CGImageGetHeight(img);

    outBuffer2.rowBytes = CGImageGetBytesPerRow(img);

    //perform convolution

    error = vImageBoxConvolve_ARGB8888(&inBuffer, &outBuffer2, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);

    if (error) {

        NSLog(@"error from convolution %ld", error);

    }

    error = vImageBoxConvolve_ARGB8888(&outBuffer2, &inBuffer, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);

    if (error) {

        NSLog(@"error from convolution %ld", error);

    }

    error = vImageBoxConvolve_ARGB8888(&inBuffer, &outBuffer, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);

    if (error) {

        NSLog(@"error from convolution %ld", error);

    }

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef ctx = CGBitmapContextCreate(outBuffer.data,

                                             outBuffer.width,

                                             outBuffer.height,

                                             8,

                                             outBuffer.rowBytes,

                                             colorSpace,

                                             (CGBitmapInfo)kCGImageAlphaNoneSkipLast);

    CGImageRef imageRef = CGBitmapContextCreateImage (ctx);

    UIImage *returnImage = [UIImage imageWithCGImage:imageRef];

    //clean up

    CGContextRelease(ctx);

    CGColorSpaceRelease(colorSpace);

    free(pixelBuffer);

    free(pixelBuffer2);

    CFRelease(inBitmapData);

    CGImageRelease(imageRef);

    return returnImage;

}

/**

 *  *改变Image的大小

 *

 *  @param size 目的大小

 *

 *  @return 修改后的Image

 */

- (UIImage *)cropImageWithSize:(CGSize)size {

    float scale = self.size.width/self.size.height;

    CGRect rect = CGRectMake(0, 0, 0, 0);

    if (scale > size.width/size.height) {

        rect.origin.x = (self.size.width - self.size.height * size.width/size.height)/2;

        rect.size.width  = self.size.height * size.width/size.height;

        rect.size.height = self.size.height;

    }else {

        rect.origin.y = (self.size.height - self.size.width/size.width * size.height)/2;

        rect.size.width  = self.size.width;

        rect.size.height = self.size.width/size.width * size.height;

    }

    CGImageRef imageRef   = CGImageCreateWithImageInRect(self.CGImage, rect);

    UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];

    CGImageRelease(imageRef);

    return croppedImage;

}