图像运算(三)——乘法(Multiplication)

描述：和其它图像操作一样，图像的乘法操作也是点对点的像素点进行操作

公式描述：O(i,j) = I1(i,j) * I2(i,j)

注意1：和其它操作一样输入图像之一也可以是一个常值(C)，即 O(i,j) = I(i,j) * C

注意2：上下限问题和循环问题，对于支持循环的图像格式来说，就不存在超过上下限问题，输出的图像像素值不管是多大，它总在上下限的范围之内进行循环。

Code:

Similarity, showing a part of kernel function：

  /**
   *Applies the image mult operator on the specified image arrays, with the specified offset and scale value
   *@param src1_1d The first source image as a pixel array
   *@param src2_1d The second source image as a pixel array
   *@param width width of the destination image in pixels
   *@param height height of the destination image in pixels
   *@param oset The offset value
   *@param scale The scale value
   *@return A pixel array containing the product of the two input images
   */

  public int [] DoMult(int [] src1_1d, int [] src2_1d, int width, int height, 
		       float oset, float scale){
    
    int place1 = -1;
    int place2 = -1;
    int src1rgb = 0;
    int src2rgb = 0;
    int result = 0;
    //Get size of image and make 1d_arrays
    d_w = width;
    d_h = height;
    
    
    dest_1d = new int[d_w*d_h];
    
    boolean firstwider = false;
    boolean secondwider = false;
    int wrap;
    
    if (i1_w > d_w){
      wrap =   ((i1_w + 1) - d_w);
      firstwider = true;
    } else if (i2_w > d_w){
      wrap =    ((i2_w + 1) - d_w);
      secondwider = true;
      
    } else {
      wrap = 0;
    }
    
    //if you know there is no wrap around, you can save yourself some time
    
    if (wrap == 0) {
      for (int i=0; i< dest_1d. length ; i++){
	src2rgb = src2_1d[i] & 0x000000ff;
	src1rgb = src1_1d[i] & 0x000000ff;
	result = (int) ((scale * ((float) src1rgb * (float) src2rgb )) + oset);
	//clip to 0 ... 255
	if (result < 0){
	  result = 0;
	} else if  (result > 255){
	  result = 255;
	}
	
	//create an int value for dest_1d
	dest_1d[i ] =  0xff000000 | (result + (result << 16) + (result << 8));
	
      }
      
      return dest_1d;
      
    }
    else {
      
      for (int i=0; i< dest_1d. length ; i++){
	
      //we might need to skip out some pixels which aren't in the overlap area
	
	if ((i %d_w  ) == 0 ) {
	  if ( i == 0 ){
	    place1 = 0;
	    place2 = 0;
	  } else if (secondwider) {
	    place2 = place2 + wrap;
	    place1 ++;
	  } else {
	    place1 = place1 + wrap;
	    place2 ++;
	  }
	} else{
	  place2 ++;
	  place1 ++;
	}
	
	src2rgb = src2_1d[place2] & 0x000000ff;
	src1rgb = src1_1d[place1] & 0x000000ff;
	
	result = (int) ((scale * ((float) src1rgb * (float) src2rgb )) + oset);
	
      //clip to 0 ... 255
	if (result < 0){
	  result = 0;
	} else if  (result > 255){
	  result = 255;
	}
	
	//create an int value for dest_1d
	dest_1d[i ] =  0xff000000 | (result + (result << 16) + (result << 8));
      }
      return dest_1d;
    }
  }

Input Image:

C=3;

Output Image：

总结：这里举例说明的是利用常数值，这样能更好的说明乘法操作的实质性。