ofImage Alpha to ofCvColor

beginners
#1

Hi

I’ve got an ofImage type=OF_IMAGE_ALPHA that I want to put into an ofCvColor image.

Are there any functions within ofw that can do this? Or whats the least processor heavy method?

This is from capturing a pointgrey cam.

Many thanks

#2

This is my code, which works, but im sure it could be quicker, possibly using memcpy and less looping?

  
  
  
unsigned char * rgbaPixels = rgbaImage.getPixels();  
  
            for(int i=0; i<rawHeight; i++){  
                for(int j=0; j<rawWidth; j++){  
                    colorRawPixels[(i*rawWidth+j)*3 + 0] = rgbaPixels[(i*rawWidth+j)*4 + 0]; // red  
                    colorRawPixels[(i*rawWidth+j)*3 + 1] = rgbaPixels[(i*rawWidth+j)*4 + 1]; // green  
                    colorRawPixels[(i*rawWidth+j)*3 + 2] = rgbaPixels[(i*rawWidth+j)*4 + 2]; // blue  
                }  
            }  
            colorRaw.setFromPixels(colorRawPixels, rawWidth, rawHeight);
#3

Here is the same with one loop.
Less calculations for where in the array you are.

  
unsigned char * rgbaPixels = rgbaImage.getPixels();   
  
//total rgb pixels  
int totalPixels = rawWidth * rawHeight * 3;  
  
int k = 0;  //for stepping through the the rgba image  
  
for(int i = 0; i < totalPixels; i+= 3){  
  colorRawPixels[i]    = rgbaPixels[k];  
  colorRawPixels[i+1] = rgbaPixels[k+1];  
  colorRawPixels[i+2] = rgbaPixels[k+2];  
  
  k+=4; //go to the next pixel for the rgba array  
}  
              
colorRaw.setFromPixels(colorRawPixels, rawWidth, rawHeight);

Technically you can make things faster by using pointers to move through the pixels - but any decent compiler will do similar optimizations to your code in the compile process, so it is best to stick with arrays and keep things readable!

I once spent the time re-writing all my image processing operations using pointers only to find 0% performance improvement - the compiler was doing the same thing behind the scenes.

Theo

#4

hi cris you can make this, i have the same problem, i want to put of_image_alpha in ofcvColor, and use cvColor for many things, i use open cv and OF 0.06… thx Crish

[quote author=“chrisoshea”]Hi

I’ve got an ofImage type=OF_IMAGE_ALPHA that I want to put into an ofCvColor image.

Are there any functions within ofw that can do this? Or whats the least processor heavy method?

This is from capturing a pointgrey cam.

Many thanks[/quote]