Editing Edge detection (section)

== Difficulty ==

Outside of images with simple objects or featuring well-controlled lighting, edge detection is not a trivial task, since it can be difficult to determine what threshold should be used to define an edge between two pixels.<ref name=lin98/> For example, in the following one-dimensional signal, most would intuitively say there is an edge between the 4th and 5th pixels:

{| style="border:0; margin:0.5em auto"
|-
| style="border:1px solid #000; padding:5px 10px;" | 5
| style="border:1px solid #000; padding:5px 10px;" | 7
| style="border:1px solid #000; padding:5px 10px;" | 6
| style="border:1px solid #000; padding:5px 10px;" | 4
| style="border:1px solid #000; padding:5px" | 152
| style="border:1px solid #000; padding:5px" | 148
| style="border:1px solid #000; padding:5px" | 149
|- style="height:30px"
| style="background:#050505" |

| style="background:#070707" |

| style="background:#060606" |

| style="background:#040404" |

| style="background:#989898" |

| style="background:#949494" |

| style="background:#959595" |
|}

However, if the intensity difference between the 4th and the 5th pixels were smaller, it would not be as easy to say that there should be an edge in the corresponding region. Similarly, if the intensity differences between the adjacent neighboring pixels were higher, one could argue that more than one edge should be considered to exist, or even none at all.

{| style="border:0; margin:0.5em auto"
|-
| style="border:1px solid #000; padding:5px 10px;" | 5
| style="border:1px solid #000; padding:5px 10px;" | 7
| style="border:1px solid #000; padding:5px 10px;" | 6
| style="border:1px solid #000; padding:5px 10px;" | 61
| style="border:1px solid #000; padding:5px" | 113
| style="border:1px solid #000; padding:5px" | 148
| style="border:1px solid #000; padding:5px" | 149
|- style="height:30px"
| style="background:#050505" |

| style="background:#070707" |

| style="background:#060606" |

| style="background:#3d3d3d" |

| style="background:#717171" |

| style="background:#949494" |

| style="background:#959595" |
|}