Color Sensor

The REV Color Sensor V3 reads color and short-range distance over I2C. Common uses are checking whether a game piece is in the intake and detecting field tape. The SDK sample is SensorColor.

Reading it

Use NormalizedColorSensor, not ColorSensor. Normalized values always run 0 to 1, while raw ColorSensor values depend on the specific sensor. The sample names the device sensor_color.

colorSensor = hardwareMap.get(NormalizedColorSensor.class, "sensor_color");

NormalizedRGBA colors = colorSensor.getNormalizedColors();

telemetry.addLine()
        .addData("Red", "%.3f", colors.red)
        .addData("Green", "%.3f", colors.green)
        .addData("Blue", "%.3f", colors.blue);

Gain

The V3 returns very low numbers in dim light, using only a little of the 0 to 1 range. Gain multiplies the raw value before normalizing. Use a higher gain in dark conditions and a lower one in bright conditions. Never go below 1. If the gain is too high every channel reads near 1 and you cannot tell colors apart.

float gain = 2;
colorSensor.setGain(gain);

Set it once during initialization.

Hue

Comparing raw channels works in fixed lighting. Hue is more stable when lighting changes. Convert with android.graphics.Color.

final float[] hsvValues = new float[3];

NormalizedRGBA colors = colorSensor.getNormalizedColors();
Color.colorToHSV(colors.toColor(), hsvValues);

telemetry.addLine()
        .addData("Hue", "%.3f", hsvValues[0])
        .addData("Saturation", "%.3f", hsvValues[1])
        .addData("Value", "%.3f", hsvValues[2]);

Hue runs 0 to 360. Red is near 0 or 360, yellow near 60, green near 120, blue near 240. Read the hue of your actual game pieces on telemetry before picking thresholds. The numbers move with distance and lighting.

Light

The sensor has an LED. Check for SwitchableLight before using it, because not every color sensor has one.

if (colorSensor instanceof SwitchableLight) {
    ((SwitchableLight) colorSensor).enableLight(true);
}

Leave it on for reading surfaces up close.

Distance

The V3 also implements DistanceSensor. Check before casting.

if (colorSensor instanceof DistanceSensor) {
    telemetry.addData("Distance (cm)", "%.3f", ((DistanceSensor) colorSensor).getDistance(DistanceUnit.CM));
}

The distance reading is only useful at very close range, and ambient light and surface reflectivity both affect it.

Example

Reports red or blue only when something is within 5 cm.

package org.firstinspires.ftc.teamcode;

import android.graphics.Color;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DistanceSensor;
import com.qualcomm.robotcore.hardware.NormalizedColorSensor;
import com.qualcomm.robotcore.hardware.NormalizedRGBA;
import com.qualcomm.robotcore.hardware.SwitchableLight;
import org.firstinspires.ftc.robotcore.external.navigation.DistanceUnit;

@TeleOp(name = "Color Sensor Example", group = "Sensor")
public class ColorSensorExample extends LinearOpMode {

    private NormalizedColorSensor colorSensor;

    @Override
    public void runOpMode() {
        colorSensor = hardwareMap.get(NormalizedColorSensor.class, "sensor_color");
        colorSensor.setGain(2);

        if (colorSensor instanceof SwitchableLight) {
            ((SwitchableLight) colorSensor).enableLight(true);
        }

        final float[] hsvValues = new float[3];

        waitForStart();

        while (opModeIsActive()) {
            NormalizedRGBA colors = colorSensor.getNormalizedColors();
            Color.colorToHSV(colors.toColor(), hsvValues);

            double cm = 100;
            if (colorSensor instanceof DistanceSensor) {
                cm = ((DistanceSensor) colorSensor).getDistance(DistanceUnit.CM);
            }

            String detected = "none";
            if (cm < 5.0) {
                if (hsvValues[0] < 30 || hsvValues[0] > 330) {
                    detected = "red";
                } else if (hsvValues[0] > 200 && hsvValues[0] < 260) {
                    detected = "blue";
                }
            }

            telemetry.addData("Object", detected);
            telemetry.addData("Hue", "%.3f", hsvValues[0]);
            telemetry.addData("Distance (cm)", "%.3f", cm);
            telemetry.update();
        }
    }
}

The hue thresholds above are a starting point, adjust them for you’re game pieces.