截取自雾霾检测机

-(float) returnGrayVale:(UInt8*)buffer withBytesPerRow:(size_t)bytesPerRow withX:(int)x withY:(int)y{

    UInt8*  tmp;

    tmp = buffer + y * bytesPerRow + x * 4; // RGBAの4つ値をもっているので、1ピクセルごとに*4してずらす

    

    // 获取图像的RGB

    UInt8 red,green,blue;

    red = *(tmp + 0);

    green = *(tmp + 1);

    blue = *(tmp + 2);

    

    //获取灰度值

    float grayValue = [self returnGrayValueWithRGB:red withGreen:green withBlue:blue];

    return grayValue;

}

-(float)ClearIndexBySobel:(UIImage*)sourceImage fromX:(int)Xpoint fromY:(int)Ypoint zoneWidth:(int)Width zoneHeihgt:(int)Height{

    

    int imageWidth = sourceImage.size.width;

    int imageHeight = sourceImage.size.height;

    

    //防止越界处理

    if (Xpoint<=0 || Xpoint>=imageWidth-1 || Ypoint<=0 || Ypoint>=imageHeight-1) {

        return -1;

    }

    

    

    //获取ref对象

    CGImageRef  imageRef;

    imageRef = sourceImage.CGImage;

    

    // 一行有多少个字节

    size_t                  bytesPerRow;

    bytesPerRow = CGImageGetBytesPerRow(imageRef);

    

    CGDataProviderRef   dataProvider;

    dataProvider = CGImageGetDataProvider(imageRef);

    

    CFDataRef   data;

    UInt8*      buffer;

    data = CGDataProviderCopyData(dataProvider);

    buffer = (UInt8*)CFDataGetBytePtr(data);

    //循环计算区域像素点获得总的梯度值

    float sum_grad = 0;

    int count = 0;

    for (int y = Ypoint; y < Ypoint + Height; y++) {

        for (int x = Xpoint; x < Xpoint + Width; x++) {

            

            //计算周边8个点的灰度值

            float gray_00 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x-1 withY:y-1];

            float gray_01 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x-1 withY:y];

            float gray_02 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x-1 withY:y+1];

            

            float gray_10 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x withY:y-1];

            float gray_12 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x withY:y+1];

            

            float gray_20 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x+1 withY:y-1];

            float gray_21 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x+1 withY:y];

            float gray_22 = [self returnGrayVale:buffer withBytesPerRow:bytesPerRow withX:x+1 withY:y+1];

            

            //计算梯度值

            float grad_x = gray_00-gray_02+2*gray_10-2*gray_12+gray_20-gray_22;

            float grad_y = gray_00+2*gray_01+gray_02-gray_20-2*gray_21-gray_22;

            

            float grad=sqrt(grad_x*grad_x+grad_y*grad_y);

            sum_grad +=grad;

            count++;

        }

    }

    

    if(count<=0){

        return 0;

    }

    

    float clearIndex = sum_grad / count;

    

    dataProvider = nil;

    data = nil;

    buffer = nil;

    

    return clearIndex;

}