Thanks to [Ignacio Segura](http://www.isegura.es/blog/stop-spam-your-site-being-invisible-honeytrap-drupal-comments-form) I have a new anti-spambot measure. Users won’t notice it (unless they browse with CSS turned off, or other such unusualness). Hopefully this will mean that a) I don’t have to “disapprove” loads of comment span every day, and b) I can allow anonymous commenting without having to approve it before it becomes visible.
Month: October 2010
Comparing edge detectors with noisy images
Thanks to Ioannis for the stimulus – I’ve [compared a Sobel edge detector with a very simple edge detector](http://parallelpoints.com/node/50)…
http://parallelpoints.com/node/50
Image processing #001a
[Ioannis mentioned another edge detector](http://www.parallelpoints.com/node/46#comment-132) he’s fond of using – so here’s a comparison.
To summarise, his method involves shifting the image 1 pixel to the right, and subtracting it from the original image. And then doing the same but shifting one pixel down instead.
This is equivalent to convolving with
[1 -1]
rather than
[1 0 -1]
[2 0 -2]
[1 0 -1]
There’s two differences that are worth commenting on:
Image processing series
I’ve begun a series of articles showing the stages of development of an image processing system. The aim is to go through from describing algorithms at a very high level in Scilab, making tradeoffs in implementation ideas, before describing the system in VHDL and comparing the results.
[Part 1 – edge detection](/node/46) is now up…
Image processing #001
# Image processing
[img_assist|nid=42|align=right|width=128]
This is the first in a group of posts, during which I’m going to work through the development of an image processing system. I’m going to start at a very high level working with some classic image processing techniques. The plan as I write this is to work down to a complete implemenation on an FPGA. In the process I’m going to demonstrate how to link the high-level descriptions to check the performance of the low-level FPGA code.
FPGA Q&A area on stack exchange
For those who don’t know [Stack Overflow](http://stackoverflow.com/), I recommend having a look round. Web Forums (Fora?) done right. A sensible and easy way of rating questions and answers and questioners and answerers. For the right subjects, a goodly group of knowledgeable people answering them… But mainly on a software theme. Sadly (for me :) FPGAs and HDLs only come up occasionally (but I try and answer when I can). Enter Stack Exchange: