图片涂抹马赛克逻辑步骤:

• 打开一张图片为前景图片
• 以前景图片生成一张虚化后的图片为背景图片
• 手指在屏幕涂抹,根据手指路径将背景图片绘制在前景图片上

- (UIImage *)transToMosaicImage:(UIImage*)orginImage blockLevel:(NSUInteger)level
{
    //获取BitmapData
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGImageRef imgRef = orginImage.CGImage;
    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);  
    CGContextRef context = CGBitmapContextCreate (nil,
                                                  width,
                                                  height,
                                                  kBitsPerComponent,        //每个颜色值8bit
                                                  width*kPixelChannelCount, //每一行的像素点占用的字节数，每个像素点的ARGB四个通道各占8个bit
                                                  colorSpace,
                                                  kCGImageAlphaPremultipliedLast);
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imgRef);
    unsigned char *bitmapData = CGBitmapContextGetData (context);
    //这里把BitmapData进行马赛克转换,就是用一个点的颜色填充一个level*level的正方形
    unsigned char pixel[kPixelChannelCount] = {0};
    NSUInteger index,preIndex;
    for (NSUInteger i = 0; i < height - 1 ; i++) {
        for (NSUInteger j = 0; j < width - 1; j++) {
            index = i * width + j;
            if (i % level == 0) {
                if (j % level == 0) {
                    memcpy(pixel, bitmapData + kPixelChannelCount*index, kPixelChannelCount);
                }else{
                    memcpy(bitmapData + kPixelChannelCount*index, pixel, kPixelChannelCount);
                }
            } else {
                preIndex = (i-1)*width +j;
                memcpy(bitmapData + kPixelChannelCount*index, bitmapData + kPixelChannelCount*preIndex, kPixelChannelCount);
            }
        }
    } 
    NSInteger dataLength = width*height* kPixelChannelCount;
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bitmapData, dataLength, NULL);
    //创建要输出的图像
    CGImageRef mosaicImageRef = CGImageCreate(width, height,
                                              kBitsPerComponent,
                                              kBitsPerPixel,
                                              width*kPixelChannelCount ,
                                              colorSpace,
                                              kCGBitmapByteOrderDefault,
                                              provider,
                                              NULL, NO,
                                              kCGRenderingIntentDefault);
    CGContextRef outputContext = CGBitmapContextCreate(nil,
                                                       width,
                                                       height,
                                                       kBitsPerComponent,
                                                       width*kPixelChannelCount,
                                                       colorSpace,
                                                       kCGImageAlphaPremultipliedLast);
    CGContextDrawImage(outputContext, CGRectMake(0.0f, 0.0f, width, height), mosaicImageRef);
    CGImageRef resultImageRef = CGBitmapContextCreateImage(outputContext);
    UIImage *resultImage = nil; 
    if([UIImage respondsToSelector:@selector(imageWithCGImage:scale:orientation:)]) {
//        float scale = [[UIScreen mainScreen] scale];
        resultImage = [UIImage imageWithCGImage:resultImageRef scale:orginImage.scale orientation:orginImage.imageOrientation];
    } else {
        resultImage = [UIImage imageWithCGImage:resultImageRef];
    }
    //释放
    if(resultImageRef){
        CFRelease(resultImageRef);
    }
    if(mosaicImageRef){
        CFRelease(mosaicImageRef);
    }
    if(colorSpace){
        CGColorSpaceRelease(colorSpace);
    }
    if(provider){
        CGDataProviderRelease(provider);
    }
    if(context){
        CGContextRelease(context);
    }
    if(outputContext){
        CGContextRelease(outputContext);
    }
    return resultImage ;
    
}