Full Court Target Detection

[Bpk9p4]

Has anyone been able to detect the targets at full court. If so how have you done it

[Greg McKaskle]

To use the lighting to detect targets at full court, you'll need to do several things.

You need to make sure you run the camera at a high enough resolution that the 4" wide lines are several pixels wide. 320x240 should do, but it may require 640x480. Get images and measure.

You'll need to calibrate the exposure on the camera to darken the normal scene more than normal. You may be able to do this just with the Brightness setting, but it may be useful to set it to auto, expose it to a bright light, and set it to hold. This will also help keep the colors from the LED ring stay saturated.

You'll need to use brighter LEDs or more of them. If this is the only place the targeting will be used, you can also use a flashlight or other lens system to narrow the beam and concentrate the light where you want it. The intensity of light drops of as distance squared, so the reflected light will be 1/4th as bright as full court as at mid-court.

Finally, you may find that the initial settings for particle size are set too low for full court detection. The .5% threshold is used to ignore particles that are smaller than a certain size. As the robot backs up, particles shrink, and at some point you need to lower the threshold to keep the recognition of the targets. .5% work out to about 400 pixels on a 320x240 image, so watch the particle area of the targets to see what range they are in.

Greg McKaskle

[Bpk9p4]

Thank you for your help. We ran tests last night and it seems like we need a much brighter light. Do you have an suggestions on lights. Also have you tried color led vs white light

[Greg McKaskle]

I purchased an LED flashlight from home depot that has a red, blue, and white setting. It is certainly bright enough from full court because of its lens. It doesn't work well up close because the cone of light from the flashlight will only be a few feet across and won't illuminate the same area as the camera sees.

I've seen teams nest the LED rings one inside the other which will increase the brightness.

I've also used bicycle safety lights to see the targets full field. Again, they aren't dispersed enough to work well up close.

You most likely need to decide between the up-close and far-away lighting or combine several on the robot.

Greg McKaskle

[dvanvoorst]

If you are not testing with an LED ring around your camera lens, make sure the light source you are using is right next to the camera. The reflected light is extremely directional and even a few inches away from the camera can make a difference. We initially tested with a separate light about 10 inches to the side, then moved it right next to the camera and the difference was dramatic. Full field target recognition is crystal clear.

[Bpk9p4]

We are using a light ring but I do not think it is bright enough. Do you do your vision processing on he cRIO?

[dvanvoorst]

yes, we are doing our vision processing on the cRIO. Are you using the NI Vision Assistant to test with? If not, you definitely want to.
If you stand directly behind your camera, while your LED ring is on, you should see the reflective tape light up quite a bit with your own eyes. If not, then try it with a flashlight for comparison. Maybe you need brighter LEDs.

[Greg McKaskle]

Good point about mounting near the camera. It is actually the angle between the source and sensor that matters. So for very distant targets, you can actually increase the distance between camera and light. The data sheet for the material will give a plot of reflected light intensity versus angle if you want to calculate how close they need to be.

The location of the processing doesn't impact the ability to detect, but it may impact how long it takes to process the image.

Greg McKaskle

[dvanvoorst]

Interesting point Greg. Our initial "poor quality" image this year was with the target just 10 feet away, but the light source probably around 10" away from the camera. Based on what you said, we probably would have had a perfectly acceptable image if we were 30 feet away instead. In any event, an LED light ring seems like the best way to go.

[Bpk9p4]

Thank you for all your help. Do you know if there is a best color light. Also last year we ran into a lot of problems with interference from other light sources. An suggestions on how to prevent this

[Greg McKaskle]

I think the best light is the one that is the most unique, bright, and that the sensor is sensitive to.

Camera sensors tend to be more sensitive to reds and greens and less sensitive to blues. This is done to mirror how human eyes perceive color. So with LEDs of the same intensity, blue may not be reported as high as the others.

LEDs are based on photon emission from various circuits. When I was a kid, all LEDs were red, no other colors available. Today, there are all colors, but the cost and brightness per cost still differ.

All together, I'd say that the color probably doesn't matter much.

If you use HSL or HSV color thresholding and a relatively narrow hue filter, you should not have that many issues with other colors. But that is why the examples also do shape and size filtering. To interfere, something has to be the right color, right blob size, aspect ratio, it has to be pretty square and hollow.

Greg McKaskle

[dvanvoorst]

I think calibrating your camera, as Greg mentioned earlier, is very important too. Otherwise the colors can get washed out when you get in a brightly lit event.
We are experimenting with infrared lighting and an infrared filter on the camera. This is looking pretty promising so far as it excludes everything but infrared.

[Bpk9p4]

we were talking about using that yesterday. Has it shown improved results?

[dvanvoorst]

I have to admit, the results have been very good so far. I've attached an image shot from probably 40' feet away in a flourescent-lit room.

[Bpk9p4]

That is very impressive. If you do not mind me asking. what camera and lights are you using? Can you use the same calibrations for the full range?