Year 12s: what will be the first way you research your future options? >>

Finding Edges

I'm taking OCR B Advancing Physics and in module 1 (imaging) it states the method of finding edges is to "subtract the N, S, E, and W, neighbours from 4 times the value of each pixel". But wouldn't that mean in any block of the same colour you would always end up with 0 (white)? But this isn't what happens in the example image they give. So is the example image wrong or the way of going about finding edges?

If anyone has the AS book and wants to check this, it's page 17.

On second thought assuming the way they suggest is correct the image could be correct as well if 0 represented that lilac colour they use and white is some minus value, but that kinda contradicts the colour representation used in the rest of the book.

I've attempted to recreate the diagram:

Before

After

After (Expected)

Reply 1

datr

Does no one know? I don't see my physics teacher for another two weeks and this will just bother me now. :P

I was thinking about it and thought multiplying by 5 instead of 4 would create a similar effect to the one they give in the example.

But here the colour on either side of the line no longer matches in the example (but that may just be as a result of the colours I chose and the colours used in the book).

The book mentions that there are more examples and excel models available on the cd, I don't have it but maybe someone who does could confirm this for me either way. Or send me this extra material so I could see for myself.

Thanks.

Reply 2

uk6458

i remember when we did this last year at AS, and we ended up having a big disscussion about the book being wrong!! i can't remember how we eventually figured it out though :confused: