如何從UIImage獲得極端分數

Question

我有這張圖像，其中包含幾個不同顏色的物體。圖像的背景是白色的。

我需要找到左上角的點和右下角的點來裁剪圖像與對象反彈。

下面的圖片只顯示了一個我需要裁剪的灰色物體（不包括小圓點和標籤），但起初我需要獲得這些極端點。

Answer 1

// Extract the bitmap data from the image 
unsigned char* imageData= [self extractImageDataForImage:self.image]; 

// Iterate through the matrix and compare pixel colors 

for (int i=0; i< height; i++){ 
    for(int j=0; j<width*4; j+=4){ // assuming we extracted the RGBA image, therefore the 4 pixels, one per component 
     int pixelIndex= (i*width*4) + j; 
     MyColorImpl* pixelColor= [self colorForPixelAtIndex:pixelIndex imageData:imageData]; 
     if([self isColorWhite:pixelColor]){ 
       // we're not interested in white pixels 
     }else{ 
      // The reason not to use UI color a few lines above is so you can compare colors in the way you want. 
      // You can say that two colors are equal if the difference for each component is not larger than x. 
      // That way you can locate pixels with equal color even if they are almost the same color. 

      // Let's say current color is yellow 

      // Get the object that contains the info for the yellow drawable 

      MyColoredObjectInformation* info= [self.coloredObjectDictionary objectForKey:pixelColor.description]; 

      if(!info){ 
       //it doesn't exist. So lets create it and map it to the yellow color 

       info= [MyColoredObjectInformation new]; 
       [self.coloredObjectDictionary setObject:info forKey:pixelColor.description]; 
      } 
      // get x and y for the current pixel 

      float pixelX= pixelIndex % (width*4); 
      float pixelY= i; 

      if(pixelX < info.xMin) 
        info.xMin= pixelX; 

      if(pixelX > info.xMax) 
        info.xMax= pixelX; 

      if(pixelY > info.yMax) 
        info.yMax= pixelY; 

      if(pixelY < info.yMin) 
        info.yMin= pixelY; 
     } 
    } 
} 

// don't forget to free the array (since it's been allocated dynamically in extractImageForDataForImage:] 
free(imageData]; 

不要忘記設置XMIN，XMAX，y最小和y爲適當的值的每個對象

@implementation MyColoredObjectInformation 

-(id)init{ 
    if(self= [super init]){ 
     self.xMin= -1; 
     self.xMax= INT_MAX; 
     self.yMin= -1; 
     self.yMax= INT_MAX; 
    } 
return self; 
} 

一件事的圖像轉換爲數據時可能發生陣列是像素不會頂部 - >底部&左 - >右。通常在將圖像轉換爲CGImage時，圖像可以旋轉。在這種情況下，你只需要爲pixelIndex，pixelX和pixelY設定不同的公式。

最後，剛剛經歷的self.coloredObjectDictionary值進行迭代，併爲每種顏色你將有兩個點代表圍繞對象P1的矩形（XMIN，YMIN）和P2（XMAX，YMAX）