截取自霧霾檢測機
-(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
// 擷取圖像的RGB
UInt8 red,green,blue;
red = *(tmp + 0);
green = *(tmp + 1);
blue = *(tmp + 2);
//擷取灰階值
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;
//防止越界處理
if (Xpoint<=0 || Xpoint>=imageWidth-1 || Ypoint<=0 || Ypoint>=imageHeight-1) {
return -1;
}
//擷取ref對象
CGImageRef imageRef;
imageRef = sourceImage.CGImage;
// 一行有多少個位元組
size_t bytesPerRow;
bytesPerRow = CGImageGetBytesPerRow(imageRef);
CGDataProviderRef dataProvider;
dataProvider = CGImageGetDataProvider(imageRef);
CFDataRef data;
UInt8* buffer;
data = CGDataProviderCopyData(dataProvider);
buffer = (UInt8*)CFDataGetBytePtr(data);
//循環計算區域像素點獲得總的梯度值
float sum_grad = 0;
int count = 0;
for (int y = Ypoint; y < Ypoint + Height; y++) {
for (int x = Xpoint; x < Xpoint + Width; x++) {
//計算周邊8個點的灰階值
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];
//計算梯度值
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;
本文轉自 卓行天下 51CTO部落格,原文連結:http://blog.51cto.com/9951038/1772569,如需轉載請自行聯系原作者