BlobDetection library: Can it find light-colored blobs instead of only dark ones?

Processing Libraries
1

Hi.

A bit puzzled with something in the blobDetection library (Julien ‘v3ga’ Gachadoat, BlobDetection library / v3ga).

I adapted the webcam script to display the blobs and also send blob coordinates over OSC.

It identifies blobs of darker color, compared to lighter surroundings.

I wanted to reverse this behavior: to get blobs for lighter image areas.

So I inserted filter(INVERT); immediately after copying the camera data into a separate image.

void draw()
{
	if (newFrame)
	{
		newFrame=false;
		scale(-1, 1);  // horizontal flip
		image(cam, 0, 0, -width, height);
		img.copy(cam, 0, 0, cam.width, cam.height, 
				0, 0, img.width, img.height);
		filter(INVERT);
		fastblur(img, 2);
		theBlobDetection.computeBlobs(img.pixels);
		drawBlobsAndEdges(true, true, true);
	}
}

Without filter(INVERT), blobs consist of darker screen areas.

With filter(INVERT), blobs consist of lighter screen areas – same areas as before.

Should I assume, then, that filter(INVERT) only affects display but does not affect the image contents?

Is there a function that inverts the actual pixel values? I go to Reference / Processing.org and search this page for “invert” and find only a Boolean “not” operator, which is certainly not the right thing.

If I wanted to track hands, for instance, currently the only way to get a meaningful result would be to wear a white shirt and black gloves. What if I wanted to wear a dark shirt and no gloves? That’s the point.

hjh

2

I want to use a sketch to track the motion of fireflies and send co-ordinates over OSC to Pure Data. So I’d love to know how this project came along? Dark blobs are no use to me, I need to track the lightest points on the camera feed! Thanks.

3

Hello @m0nsterm0vi3 ,

This topic may be of interest to you:

I adapted this example:
https://processing.org/reference/libraries/video/Capture.html

And this code (modify example above) will invert and display the image:

void draw() {
  if (cam.available() == true) {
    cam.read();
  }
  
  image(cam, 0, 0);
  
  PImage img = cam.copy();
  
  img.filter(INVERT);
  image(img, width/2, 0); // Moved it over
}

:)