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 p_w_picpathWidth = sourceImage.size.width;
int p_w_picpathHeight = sourceImage.size.height;
//防止越界处理
if (Xpoint<=0 || Xpoint>=p_w_picpathWidth-1 || Ypoint<=0 || Ypoint>=p_w_picpathHeight-1) {
return -1;
}
//获取ref对象
CGImageRef p_w_picpathRef;
p_w_picpathRef = sourceImage.CGImage;
// 一行有多少个字节
size_t bytesPerRow;
bytesPerRow = CGImageGetBytesPerRow(p_w_picpathRef);
CGDataProviderRef dataProvider;
dataProvider = CGImageGetDataProvider(p_w_picpathRef);
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;
}
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