Re: Re: comparing two images and detecting differences

[bean]

I think comparing edges only may be the key (excellent link, JoshuaD). The edges should capture the features of the coins being compared. Simply comparing images will not work - here's why.

The actual (raised) features of the coin - a capital "I" followed by a capital "T".

++++++++++++++++++++
++++++++++++++++++++
++######++++######++
++++##++++++++##++++
++++##++++++++##++++
++++##++++++++##++++
++######++++++##++++
++++++++++++++++++++
++++++++++++++++++++

Here's how the coin would photograph lit from the lower left. Legend: "+" for the metal's "normal" color, "_" for highlights, and "#" for shadows.

++++++++++++++++++++
++######++++######++
+_++++++#++_++++++#+
++__++__++++__++__++
+++_++#++++++_++#+++
++##++##+++++_++#+++
+_++++++#++++_++#+++
++______++++++__++++
++++++++++++++++++++

Here's how the coin would photograph lit from the lower right.

++++++++++++++++++++
++######++++######++
+#++++++_++#++++++_+
++__++__++++__++__++
+++#++_++++++#++_+++
++##++##+++++#++_+++
+#++++++_++++#++_+++
++______++++++__++++
++++++++++++++++++++

And here's how it would photograph lit dead on.

____________________
__######____######__
_#______#__#______#_
__##__##____##__##__
___#__#______#__#___
__##__##_____#__#___
_#______#____#__#___
__######______##____
____________________

The edges for all three images would (I think) all look like the last image.