Feature Extraction and Image Processing for Computer Vision, 4th Edition

5.2. Thresholding and subtraction

Thresholding is a simple shape extraction technique, as illustrated in Section 3.3.4, where the images could be viewed as the result of trying to separate the eye from the background. If it can be assumed that the shape to be extracted is defined by its brightness, then thresholding an image at that brightness level should find the shape. Thresholding is clearly sensitive to change in illumination: if the image illumination changes then so will the perceived brightness of the target shape. Unless the threshold level can be arranged to adapt to the change in brightness level, any thresholding technique will fail. Its attraction is simplicity: thresholding does not require much computational effort. If the illumination ...