FIG. 1.

Edge detection procedure. The images in panels B and C were binarized in order to visualize image structure, while calculations were performed with nonbinarized images. (A) Cutout of the original image. (B) Image after application of the Marr-Hildreth operator with 3×3 kernel, thresholded to gray level 1 for contrast. (C) Image after application of a rank 3 filter. (D) Binary image after thresholding to gray level 2. (E) Image after small particles were removed by using an erosion algorithm. When the results are compared with the original image, it must be realized that the image was represented in 1,024 gray levels, whereas the human eye can discern only approximately 100 gray levels. Because of this, some of the objects detected were too faint to be visible, and some bright objects were too small to be accepted.