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How pixy's color tracking removes the effects of lighting changes


#1

I’m trying to figure out how the pixy deal with the effects of lighting changing in a scene. And can I interpret the region grow as segmentation using the thresholds? Thanks!


#2

Hello,
“interpret the region grow as segmentation using the thresholds”. I’m not sure what you mean by "region grow and which thresholds you are referring to.

Edward


#3

Thanks for your reply, Firstly I mainly want to know how pixy’s color tracking eliminates the effects of lighting changes. And secondly, pixy using region grow for color target extraction in tracking, so can I understand the region grow as using the parameters ‘u’ and ‘v’ defined in the program as color thresholds for target extraction?


#4

Hello,
Pixy focuses on the hue instead of the brightness of the object. It does this by forming a pure hue in 2 dimensions –
U = (R-G)/Y
V = (B-G)/Y

where R=red, G=green, B=Blue, Y=R+G+B

It then determines what bounds of U and V are associated with a given object.

Since it divides by Y, the brightness is mostly ignored and changes in lighting have less of an effect.

Pixy does not use region growing when tracking/detecting objects.

Hope this helps!

Edward


#5

Thanks!
In the source code,
U = (((R-G)<<15)/Y)
V = (((B-G)<<15)/Y)
Does this mean to increase the (R-G) and (B-G) by 2^15 times and then divides by Y? And are the variable types of U and V int32 or others?


#6

Hello,
I believe you are correct about everything.

Edward


#7

Thanks for your reply!