Edge detection is a function that finds edges in the current view. Select the function 'Edge detection' and you will see an image like this one:
Remark: This is not simply a black/white image. As you can see, the white wall is black...
On the options panel, you can set a threshold value. If you decrease this value, more edges will be detected:
Unfortunately, decreasing the threshold comes along with noise (single white pixels that should be there). You can remove some noise by selecting 'Remove noise'. You will get a cleaner image:
Last oprion is the 'greyscale mode'. If it is checked (default), the edges are calculated based on the greyscale image, because this is faster and suitable in most situation. However, in some cases you might need to use the color mode. Here is an example for this:
As you can see, the edges of the pants of the teddy bear can be clearly seen in the color picture, but hardly in the greyscale one. The robot will have the same problem. If you use 'greyscale mode', Evo will not recognize the edges of the pants:
But if you use color mode (disable greyscale mode), it will: