The blob tool binarizes the grayscale input image into a black and white image. Every pixel with a grayscale value below the Threshold value is set to black, with a grayscale value of zero. Every pixel with a grayscale value above the Threshold value is set to white, with a grayscale value of 255.
Adjust the threshold so that the workpiece and its background are opposite colors. If the background is light, adjust the threshold so that the background is white and the workpiece is black. If the background is dark, adjust the threshold so that the background is black and the workpiece is white.