Re: Low cost vision system, thoughts

JGCASEY wrote:


jgc wrote:

Why? Color is invariant to position and rotation
and many things can be identified by color alone.

mlw wrote:

Using color to identify things is tricky, if the
lighting varies, i.e. illumination with an incandescent
light, fluorescent light, or even candle light, or even
if the position of the sun and the weather all affect
color. (I used to do a lot photography and contracted
at Polaroid for their electronic camera) The issue of
color mapping is huge in imaging, you can't rely on
color at all unless you have control over illumination
and color response of the imaging device.


To use color reliably, you would have to do an amount
of imagine processing on the image just to normalize
the RGB data into some known color space.

...

I am aware of the problems you mention above.

The human vision system of course uses neighbouring
colors to decide what color something is thus yellow
(in RGB values) can look brown, and shade also is
a relative value not the absolute pixel value.

Yet color can be used, see D Herring post below,
"Use CMVision to quickly find colored objects"
http://www.cs.cmu.edu/~jbruce/cmvision/


In an experiment I did I used the R:G:B ratio
to locate (blob and thus outline) balls of
different colors. The light source was constant
and I guess it might not have worked in sunlight
or another type of light source without a different
set of ratios.

That is sort of the problem, variable light sources create different color
ratios, if you have more yellow light, your objects look yellow. If you had
some sort of reference in the camera view at all times, then you could do
it.


.

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