Dec 30, 2010

Video of Information visualization workshop at SUST

This is a video clip of me teaching a class at the Information visualization workshop in SUST at 28th February 2010. This clip only shows Halo among the many information visualization techniques I discussed about.

Hope this will be helpful to my students. Apologies for not so good videography.

Lab color model is preferred for computer vision

For working with computer vision and image processing, I prefer using Lab to other popular color models like RGB and CMYK. Unlike the RGB and CMYK color models, Lab color is designed to approximate human vision. It aspires to perceptual uniformity. Perceptually uniform means that a change of the same amount in a color value should produce a change of about the same visual importance. The L compoent in Lab closely matches human perception of lightness while a and b components represent stimulation along the color opponent dimensions of red-green and blue-yellow respectively.

The Lab color space is a color-opponent space. The color opponent theory states that the human visual system interprets color information by processing signals from cones and rods in an antagonistic manner. The three types of cones have some overlap in the wavelengths of light to which they respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent color theory suggests that there are three opponent channels: red versus green (a component in Lab), blue versus yellow (b component in Lab), and black versus white (L component in Lab). Responses to one color of an opponent channel are antagonistic to those to the other color.

Dec 16, 2010

Gasteracantha Arcuata : Bizarre looking spider in Lawachhora

Found this bizarre looking spider in Lawachhora forest. It was a late autumn morning on 29th November, 2010. A little research on the internet after coming back home reveals that this spider belongs to the genus Gasteracantha. The common name is Spiny-backed orb-weavers or Spiny orb-weavers because of their spiny abdomen and ability to weave vertical orb webs.


The observed specimen belongs to the species Gasteracantha arcuata. It has two long curved spines on its back and black/dark gray color all over. According to the sources on the internet[*], this species is found in Malaysia, Indonesia, Thailand, India and China. Sightings of this species in Bangladesh is probably not well documented. From my last expedition to Lawachhora forest however, it is evident that this species is abundant in that area.

I'm planning an expedition for collecting more information on this species and documenting its behavior. Hopefully I'll meet these critters in Lawachhora again at the end of December, 2010.

Here are some more photos of this species found on the internet.