Wednesday, June 10, 2009

Edges..

Today, I was just sitting in the balcony. It is quitea windy breeze outside. This view is possible if we rotate our head parallel (almost) to the earth plane and around 75 degree right to the window/balcony surface normal. :D

Well, my thoughts didn't stop there. I was thinking about the way my damn brain might process this visual and suddenly this question popped up!! What gives an object its shape? (in a 2D world)...... tha dhan.. "Edges.. "

I took Sravan's camera took one non-sense picture and tried to process it out with Gimp.

Steps are these..
1. Filters -> Edge Detect -> Difference of Gaussians with R1 as 3 and R2 as 1 (pixels)
2. Colors -> Levels and tweaked it until I got the required contrast
3. Image -> Scale to 1200

And I was going through this Difference of Gaussian Algorithm. Well, I could pick up something.. here

The Algo is quite simple.. convert the image to grey scale and independently blur it at two radii and subtract one from the other.. :) (This entire thing is done with one click in Gimp)

Going into the details, if we look at any picture in grey scale and intensity coding (0-256) as some damn field and convert it into Fourier space, the high frequency modes are responsible for the sudden changes in the field (that is black intensity). So.. what does Gaussian blur do..?? It will suppress high frequency modes :). In our Algo.. different radii for the two blurred images will suppress the high frequency modes to different extent.. so if we remove one from the other.. we will get.. the EDGE..
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