a simple program can sweep through a color spectrum and the peak reflection point should correspond to the detected color.

There’s no point ‘sweeping the spectrum’. The best you could do is do red, green and blue one after another, thus giving you the RGB colour of the object. This should let you distinguish any colour, including white.

Nice idea, not sure how well it would work in practice.

i like the idea of detecting the objects actual color by lighting it up in red, green and blue and analyzing the amount of reflected light. i just wonder how that technique works with more or less reflecting surfaces.

my thoughts as well frac. or like andres says, quickly sweep through all colours instead of having to manually select the colour.

wwhat: i guess you could do that, but how would you know what color you are trying to detect? you’d have to have some LCD display with the RGB values or something like that. And an ultrabright white LED was the same cost as the RGB led

But the UV sensor is an interesting idea…

the point is using three filters method you can constantly output the colour on the rgb led of the receved light. if the intensity is above a certain threshold, or it changes suddenly etc (use your imagination) then there is an object there.

edz-
That’s exactly how an old Perkin-Elmer UV-Visible Spectrophotometer works. There’s a nice broadband (mercury-arc or incandescent, don’t recall) light source, a prism (you could use a diffraction grating, I believe), and a pair of vacuum-tube photodetectors in a Wheatstone Bridge configuration to tare out the reference beam. They’re set up as absorption detectors for chemistry, but could probably be convinced to work as very good colorimeters if you were so inclined.
ebay has a few of ‘em, if you’re interested in experimenting.

oh yeah, thats a good point, a white led probably deficient in the color spectrum!

This is the very same principle as scanners, they have a cold cathode led, and then a long sensor that detects the amount of reflected light in every color. somethin’ like that…

I think my scanner does this. While it appears to sweep a white light over the page if you move your head you can clearly make out Red Blue and Green

I was disappointed to read that it needed a photoresistor. I will be impressed as soon as the LED alone detects the color. And having to manually set the color makes it even more lame. Sorry.

I’d love to see a multi-color version of this: http://cs.nyu.edu/~jhan/ledtouch/index.html :)

you’d want to use a photodiode for color detection.
a cmos sensor or ccd would be what you would use for image scanning. The planon docupen scanner (rc800 plastic piece of crap from hell, don’t buy) used the RGB cycling method (with a tri-color LED) to produce color scans. Therefore the scanner did not actually see in color, it just sampled the light intensities in red, green and blue independently to come up with an interpretation of a color image.

1.) You can’t “sweep the spectrum” with the finite number of peaks (in this case three) you get with LEDs.

2.) You guys all don’t know what colors are, except for diddle who used his/her brain. And there are no “complementary colors” except in our brains. Let me try:

(skip this paragraph if you are scared)
Multiply the light source’s color spectrum with the material’s reflectance spectrum and you get the “color” that reaches the eye/camera. Now multiply that with the response spectra of the cones in the eye or the camera’s CCD chip and integrate. (By multiplying these functions i mean something like f*g(x)=f(x)*g(x).) Now you have a color value.

With your method you will get values that look about right in most cases, but consider some material that has a reflectance spectrum with one peak (say, yellow) between two peaks of your leds (say, red and green). This will show up as black when illuminated with the seemingly yellow light of the combined leds, although it appears yellow under full-spectrum light like sunlight.

(ok, it will not be black since the peaks are of some width and maybe even overlap. But it will be darker than it should be, which is my point.)

Read wikipedia, it helped me.

Can someone tell me what are the cool technology on color detection or other similar ideas?

me and my partner, undergrad students, would like to make a thesis topic out of it. Course is Electronics and Communications Engineering.

we would very much appreciate your help, thank you very much.