Vision Tracking the Hot Goal LEDs

[Dadwolo4]

Does anyone know the wavelength color of the hot goal LED?

[faust1706]

Originally Posted by Dadwolo4

Does anyone know the wavelength color of the hot goal LED?

Adding to this question: Does anyone have any concerns with the variation in light affecting seeing the leds? I personally don't think slight lighting variations should make much of a difference, but I am interested in other people's thoughts on the matter.

[Greg McKaskle]

What you really care about is what color the camera sees when it captures the LEDs, not what color the LEDs produce.

If you had a perfectly calibrated camera, knowing the LED wavelength would be all you'd need. But we don't have perfect cameras or perfect eyes.

One of the first things the cameras do is to combine the component light values into a colored image assuming a specified white balance. This is there to adjust for different ambient lighting such as outdoor sunlight versus indoor fluorescent. But this shifts all colors in the image. It doesn't know what pixels represent an LED producing light source and the pixels that are reflecting ambient light. The camera offers different white balance settings including an auto setting that analyzes the image and calculates the most likely type of ambient lighting. But all of these shift the colors, breaking simple math comparison approaches.

I think the first challenge is to determine if you can even get the camera to see the colors. Bright light sources saturate the sensor, resulting in a white spot, not a colored spot. Perhaps you can simply use the monochrome spots as a template for image recognition?

Greg McKaskle

[mwtidd]

I personally wouldn't try to see the color specifically but rather the brightness. You could align your robot left or right of the center of the goal, but in a position that the camera can see both the left and right sides of the I. With some pretty simple brightness filters, you should be able to detect if your side or the other side is hotter.

If you are only using this to detect hotness, then I would also align the camera so the target is in the top portion of your view, that way you can filter out the lower section. Given you have a line for alignment you may even want to filter out some of the area in the middle of the goal to avoid noise from the crowd etc.

If you're using rgb, you could use a custom threshold like minimum of rgb, or if your camera sees the yellow you could use a min average threshold of RG.

Then split you screen into three columns and calculate the average brightness of the three. If you're in the hot side two of the three should show up as hot, if you're on the cold side, only one of the three should show up hot.

[plnyyanks]

Originally Posted by lineskier

I personally wouldn't try to see the color specifically but rather the brightness. You could align your robot left or right of the center of the goal, but in a position that the camera can see both the left and right sides of the I. With some pretty simple brightness filters, you should be able to detect if your side or the other side is hotter.

Be careful with this approach, though. Just make sure you find a way to filter out the field lighting, which will definitely be brighter than your shop and could confuse your system.

[rsisk]

What are teams using to practice with? Any particular led strips people are putting on practice goals?

[mwtidd]

Originally Posted by rsisk

What are teams using to practice with? Any particular led strips people are putting on practice goals?

I found these LEDs that seem to match closely the philips ones on the field.

The philips ones are spaced 3 or 4 inches apart, couldn't figure out exactly which strip they were using.

yellow:
http://www.superbrightleds.com/morei...-mcd/362/1309/

blue:
http://www.superbrightleds.com/morei...-mcd/359/1306/

red:
http://www.superbrightleds.com/morei...-mcd/361/1308/.


I also second rsisk's statement. The light's you use really won't make much a difference, because you will need to have a pretty good filter in place that works in many different lighting environments to minimize calibration necessary on the field (I'm guessing the practice field won't have this lighting).

Also remember, you have a 50/50 chance at hitting the hot goal so it's only worth on average ~2.5 points, so take that into account when you prioritize your programming tasks.

[Tom Line]

Tightening up your color constraints too much is a mistake. Ambient lighting definitely will affect your vision.

In addition, don't rely on just seeing one shape.

The most accurate vision systems will be those that combine the two approaches. They will look for the correctly color using fairly wide open constraints, look for shapes with fairly wide open constraints, then check the shapes position and verify their colors.

In other words, your vision system should check that what you see is around the right color, about the right shape, and has approximately the correct spacial relationship to the other target (vertical versus horizontal). This will result in a much higher % chance of you identifying the correct object and state.