ColorBlobLocatorProcessor

What is ColorBlobLocatorProcessor?

ColorBlobLocatorProcessor is a built-in VisionPortal processor that detects colored objects (blobs) in the camera feed. It handles the complex OpenCV operations for you, providing a simple API for common detection tasks.

Perfect for:

Detecting team props
Finding game elements by color
Alliance-specific detection
Quick prototyping

Basic Usage

Creating the Processor

Java:

ColorBlobLocatorProcessor colorProcessor = new ColorBlobLocatorProcessor.Builder()
    .setTargetColorRange(ColorRange.BLUE)  // What color to find
    .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
    .setRoi(ImageRegion.entireFrame())      // Where to look
    .setDrawContours(true)                  // Draw on preview
    .setBlurSize(5)                         // Noise reduction
    .build();

Kotlin:

val colorProcessor = ColorBlobLocatorProcessor.Builder()
    .setTargetColorRange(ColorRange.BLUE)
    .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
    .setRoi(ImageRegion.entireFrame())
    .setDrawContours(true)
    .setBlurSize(5)
    .build()

Getting Results

Java:

// Get all detected blobs
List<ColorBlobLocatorProcessor.Blob> blobs = colorProcessor.getBlobs();

// Filter by area (min 100px, max 5000px)
ColorBlobLocatorProcessor.Util.filterByArea(100, 5000, blobs);

// Sort by size (largest first)
ColorBlobLocatorProcessor.Util.sortByArea(
    ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
);

// Get the largest blob
if (!blobs.isEmpty()) {
    ColorBlobLocatorProcessor.Blob largest = blobs.get(0);
    
    // Get position
    RotatedRect box = largest.getBoxFit();
    double x = box.center.x;
    double y = box.center.y;
    
    // Get properties
    double area = largest.getContourArea();
    double density = largest.getDensity();
    double aspectRatio = largest.getAspectRatio();
}

Kotlin:

// Get all detected blobs
val blobs = colorProcessor.blobs

// Filter by area (min 100px, max 5000px)
ColorBlobLocatorProcessor.Util.filterByArea(100.0, 5000.0, blobs)

// Sort by size (largest first)
ColorBlobLocatorProcessor.Util.sortByArea(
    ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
)

// Get the largest blob
if (blobs.isNotEmpty()) {
    val largest = blobs[0]
    
    // Get position
    val box = largest.boxFit
    val x = box.center.x
    val y = box.center.y
    
    // Get properties
    val area = largest.contourArea
    val density = largest.density
    val aspectRatio = largest.aspectRatio
}

Builder Configuration

Target Color Range

Choose from predefined color ranges:

.setTargetColorRange(ColorRange.BLUE)
.setTargetColorRange(ColorRange.RED)
.setTargetColorRange(ColorRange.YELLOW)
.setTargetColorRange(ColorRange.GREEN)

Or define a custom range:

ColorRange customRange = new ColorRange(
    ColorSpace.YCrCb,                          // Color space
    new Scalar(0, 0, 150),                      // Lower bound
    new Scalar(255, 120, 255),                  // Upper bound
    ColorBlobLocatorProcessor.Scalar.RANGE_THRESHOLD  // Threshold
);

.setTargetColorRange(customRange)

Region of Interest (ROI)

Only process specific parts of the image:

// Entire frame
.setRoi(ImageRegion.entireFrame())

// Custom rectangle (x, y, width, height)
.setRoi(ImageRegion.asUnityCenterCoordinates(
    -0.5, -0.5,  // Top-left corner (-1 to 1)
    0.5, 0.5     // Bottom-right corner
))

// Pixel coordinates
ImageRegion customRoi = new ImageRegion() {
    @Override
    public Rect asImageCoordinates(int imageWidth, int imageHeight, 
                                   CameraCalibration calibration) {
        return new Rect(100, 100, 400, 300);  // x, y, width, height
    }
};
.setRoi(customRoi)

Contour Mode

Control which contours are detected:

// External contours only (default, fastest)
.setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)

// All contours (including holes)
.setContourMode(ColorBlobLocatorProcessor.ContourMode.ALL)

Visual Feedback

Draw detection results on the preview:

// Draw contours around detected blobs
.setDrawContours(true)

// Configure box drawing
.setBoxFit(ColorBlobLocatorProcessor.BoxFit.ROTATE)  // Rotated rectangle
.setBoxFit(ColorBlobLocatorProcessor.BoxFit.NONE)    // No box

Noise Reduction

Apply Gaussian blur to reduce noise:

// Blur size (odd number, 0 to disable)
.setBlurSize(5)  // 5x5 blur kernel

Higher values = more blur = less noise but also less detail.

Blob Properties

Each detected blob provides useful information:

Position Data

RotatedRect boxFit = blob.getBoxFit();

// Center position
double centerX = boxFit.center.x;
double centerY = boxFit.center.y;

// Box dimensions
double width = boxFit.size.width;
double height = boxFit.size.height;

// Rotation angle
double angle = boxFit.angle;

Shape Analysis

// Contour area (in pixels)
double area = blob.getContourArea();

// Density (how "filled" the blob is, 0-1)
double density = blob.getDensity();

// Aspect ratio (width / height)
double aspectRatio = blob.getAspectRatio();

// Bounding box
Rect boundingBox = blob.getContour().boundingRect();

Raw Contour

Access the raw OpenCV contour for advanced analysis:

MatOfPoint contour = blob.getContour();
// Use with OpenCV functions

Filtering and Sorting

Filter by Area

Keep only blobs within size range:

// Minimum pixels, maximum pixels
ColorBlobLocatorProcessor.Util.filterByArea(200, 5000, blobs);

Filter by Density

Keep only "solid" blobs:

// Minimum density (0.0 to 1.0)
ColorBlobLocatorProcessor.Util.filterByDensity(0.7, blobs);

Filter by Aspect Ratio

Keep only blobs with certain proportions:

// Minimum ratio, maximum ratio
ColorBlobLocatorProcessor.Util.filterByAspectRatio(0.5, 2.0, blobs);

Sort Blobs

// By area
ColorBlobLocatorProcessor.Util.sortByArea(SortOrder.DESCENDING, blobs);
ColorBlobLocatorProcessor.Util.sortByArea(SortOrder.ASCENDING, blobs);

// By density
ColorBlobLocatorProcessor.Util.sortByDensity(SortOrder.DESCENDING, blobs);

Complete Example: Team Prop Detection

This example detects a team prop and determines its position (left/center/right):

Java:

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import org.firstinspires.ftc.robotcore.external.hardware.camera.WebcamName;
import org.firstinspires.ftc.vision.VisionPortal;
import org.firstinspires.ftc.vision.opencv.ColorBlobLocatorProcessor;
import org.firstinspires.ftc.vision.opencv.ColorRange;
import org.firstinspires.ftc.vision.opencv.ImageRegion;
import org.opencv.core.RotatedRect;
import java.util.List;

@Autonomous(name = "Team Prop Detection")
public class TeamPropAuto extends LinearOpMode {
    
    enum PropPosition {
        LEFT,
        CENTER,
        RIGHT,
        NOT_FOUND
    }
    
    private VisionPortal visionPortal;
    private ColorBlobLocatorProcessor colorProcessor;
    
    @Override
    public void runOpMode() {
        
        // Create color processor for blue team prop
        colorProcessor = new ColorBlobLocatorProcessor.Builder()
            .setTargetColorRange(ColorRange.BLUE)
            .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
            .setRoi(ImageRegion.entireFrame())
            .setDrawContours(true)
            .setBlurSize(5)
            .build();
        
        // Create VisionPortal
        visionPortal = new VisionPortal.Builder()
            .setCamera(hardwareMap.get(WebcamName.class, "Webcam 1"))
            .addProcessor(colorProcessor)
            .build();
        
        // Wait for camera to start
        while (!isStarted() && !isStopRequested()) {
            PropPosition position = detectPropPosition();
            telemetry.addData("Prop Position", position);
            telemetry.addData("Status", "Ready! Press Play");
            telemetry.update();
            sleep(50);
        }
        
        // Get final position reading
        PropPosition finalPosition = detectPropPosition();
        
        // Disable processor to save resources
        visionPortal.setProcessorEnabled(colorProcessor, false);
        
        waitForStart();
        
        // Use detected position for autonomous
        switch (finalPosition) {
            case LEFT:
                telemetry.addLine("Going LEFT");
                // Execute left path
                break;
            case CENTER:
                telemetry.addLine("Going CENTER");
                // Execute center path
                break;
            case RIGHT:
                telemetry.addLine("Going RIGHT");
                // Execute right path
                break;
            case NOT_FOUND:
                telemetry.addLine("Prop not found, using default");
                // Execute default path
                break;
        }
        telemetry.update();
        
        sleep(2000);
        visionPortal.close();
    }
    
    private PropPosition detectPropPosition() {
        // Get detected blobs
        List<ColorBlobLocatorProcessor.Blob> blobs = colorProcessor.getBlobs();
        
        // Filter: area between 500-10000 pixels, density > 0.6
        ColorBlobLocatorProcessor.Util.filterByArea(500, 10000, blobs);
        ColorBlobLocatorProcessor.Util.filterByDensity(0.6, blobs);
        
        // Sort by size (largest first)
        ColorBlobLocatorProcessor.Util.sortByArea(
            ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
        );
        
        // Return position UNKNOWN if no blobs found
        if (blobs.isEmpty()) {
            return PropPosition.NOT_FOUND;
        }
        
        // Get largest blob
        ColorBlobLocatorProcessor.Blob largestBlob = blobs.get(0);
        RotatedRect boxFit = largestBlob.getBoxFit();
        double centerX = boxFit.center.x;
        
        // Determine position based on X coordinate
        // Assuming 640px wide image
        if (centerX < 213) {
            return PropPosition.LEFT;
        } else if (centerX < 427) {
            return PropPosition.CENTER;
        } else {
            return PropPosition.RIGHT;
        }
    }
}

Kotlin:

package org.firstinspires.ftc.teamcode

import com.qualcomm.robotcore.eventloop.opmode.Autonomous
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode
import org.firstinspires.ftc.robotcore.external.hardware.camera.WebcamName
import org.firstinspires.ftc.vision.VisionPortal
import org.firstinspires.ftc.vision.opencv.ColorBlobLocatorProcessor
import org.firstinspires.ftc.vision.opencv.ColorRange
import org.firstinspires.ftc.vision.opencv.ImageRegion

@Autonomous(name = "Team Prop Detection")
class TeamPropAuto : LinearOpMode() {
    
    enum class PropPosition {
        LEFT, CENTER, RIGHT, NOT_FOUND
    }
    
    private lateinit var visionPortal: VisionPortal
    private lateinit var colorProcessor: ColorBlobLocatorProcessor
    
    override fun runOpMode() {
        
        // Create color processor for blue team prop
        colorProcessor = ColorBlobLocatorProcessor.Builder()
            .setTargetColorRange(ColorRange.BLUE)
            .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
            .setRoi(ImageRegion.entireFrame())
            .setDrawContours(true)
            .setBlurSize(5)
            .build()
        
        // Create VisionPortal
        visionPortal = VisionPortal.Builder()
            .setCamera(hardwareMap.get(WebcamName::class.java, "Webcam 1"))
            .addProcessor(colorProcessor)
            .build()
        
        // Wait for camera to start
        while (!isStarted && !isStopRequested) {
            val position = detectPropPosition()
            telemetry.addData("Prop Position", position)
            telemetry.addData("Status", "Ready! Press Play")
            telemetry.update()
            sleep(50)
        }
        
        // Get final position reading
        val finalPosition = detectPropPosition()
        
        // Disable processor to save resources
        visionPortal.setProcessorEnabled(colorProcessor, false)
        
        waitForStart()
        
        // Use detected position for autonomous
        when (finalPosition) {
            PropPosition.LEFT -> {
                telemetry.addLine("Going LEFT")
                // Execute left path
            }
            PropPosition.CENTER -> {
                telemetry.addLine("Going CENTER")
                // Execute center path
            }
            PropPosition.RIGHT -> {
                telemetry.addLine("Going RIGHT")
                // Execute right path
            }
            PropPosition.NOT_FOUND -> {
                telemetry.addLine("Prop not found, using default")
                // Execute default path
            }
        }
        telemetry.update()
        
        sleep(2000)
        visionPortal.close()
    }
    
    private fun detectPropPosition(): PropPosition {
        // Get detected blobs
        val blobs = colorProcessor.blobs
        
        // Filter: area between 500-10000 pixels, density > 0.6
        ColorBlobLocatorProcessor.Util.filterByArea(500.0, 10000.0, blobs)
        ColorBlobLocatorProcessor.Util.filterByDensity(0.6, blobs)
        
        // Sort by size (largest first)
        ColorBlobLocatorProcessor.Util.sortByArea(
            ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
        )
        
        // Return NOT_FOUND if no blobs found
        if (blobs.isEmpty()) {
            return PropPosition.NOT_FOUND
        }
        
        // Get largest blob
        val largestBlob = blobs[0]
        val boxFit = largestBlob.boxFit
        val centerX = boxFit.center.x
        
        // Determine position based on X coordinate
        // Assuming 640px wide image
        return when {
            centerX < 213 -> PropPosition.LEFT
            centerX < 427 -> PropPosition.CENTER
            else -> PropPosition.RIGHT
        }
    }
}

Tuning Tips

###1. Choose the Right Color Space

YCrCb - Best for FTC alliance colors (red/blue)
HSV - Good general-purpose choice
RGB - Least reliable, avoid if possible

2. Test Lighting Conditions

Tune parameters under:

Bright field lights
Dim lighting
With camera auto-exposure

3. Use Appropriate Filters

// Too restrictive: may miss objects
filterByArea(2000, 3000, blobs);  // Very narrow range
filterByDensity(0.95, blobs);      // Nearly perfect

// Just right: catches most cases
filterByArea(500, 5000, blobs);    // Reasonable range
filterByDensity(0.6, blobs);       // Allows imperfect detection

4. Handle Edge Cases

// Always check if blobs list is empty
if (!blobs.isEmpty()) {
    // Process blobs
} else {
    // Use default behavior
}

5. ROI for Performance

Limit search area to where objects appear:

// Only check bottom half of frame
.setRoi(ImageRegion.asUnityCenterCoordinates(-1, 0, 1, 1))

Troubleshooting

No Blobs Detected

Causes:

Wrong color range
Lighting too bright/dark
Object outside ROI
Filters too restrictive

Solutions:

Verify color range with EOCV-Sim
Adjust thresholds
Expand ROI
Loosen filters

Too Many False Positives

Causes:

Color range too broad
No area filtering
Similar colored background

Solutions:

Narrow color thresholds
Add filterByArea() and filterByDensity()
Use ROI to exclude background

Poor Performance

Causes:

High resolution
Large ROI
Complex scene

Solutions:

Reduce camera resolution
Restrict ROI
Increase blur size
Disable live view

Next Steps

Learn AprilTag Detection for precise localization
Create Custom VisionProcessors for advanced needs
See Integration Patterns for subsystem architecture

What is ColorBlobLocatorProcessor?

Perfect for:

Detecting team props
Finding game elements by color
Alliance-specific detection
Quick prototyping

Basic Usage

Creating the Processor

Java:

ColorBlobLocatorProcessor colorProcessor = new ColorBlobLocatorProcessor.Builder()
    .setTargetColorRange(ColorRange.BLUE)  // What color to find
    .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
    .setRoi(ImageRegion.entireFrame())      // Where to look
    .setDrawContours(true)                  // Draw on preview
    .setBlurSize(5)                         // Noise reduction
    .build();

Kotlin:

val colorProcessor = ColorBlobLocatorProcessor.Builder()
    .setTargetColorRange(ColorRange.BLUE)
    .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
    .setRoi(ImageRegion.entireFrame())
    .setDrawContours(true)
    .setBlurSize(5)
    .build()

Getting Results

Java:

// Get all detected blobs
List<ColorBlobLocatorProcessor.Blob> blobs = colorProcessor.getBlobs();

// Filter by area (min 100px, max 5000px)
ColorBlobLocatorProcessor.Util.filterByArea(100, 5000, blobs);

// Sort by size (largest first)
ColorBlobLocatorProcessor.Util.sortByArea(
    ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
);

// Get the largest blob
if (!blobs.isEmpty()) {
    ColorBlobLocatorProcessor.Blob largest = blobs.get(0);
    
    // Get position
    RotatedRect box = largest.getBoxFit();
    double x = box.center.x;
    double y = box.center.y;
    
    // Get properties
    double area = largest.getContourArea();
    double density = largest.getDensity();
    double aspectRatio = largest.getAspectRatio();
}

Kotlin:

// Get all detected blobs
val blobs = colorProcessor.blobs

// Filter by area (min 100px, max 5000px)
ColorBlobLocatorProcessor.Util.filterByArea(100.0, 5000.0, blobs)

// Sort by size (largest first)
ColorBlobLocatorProcessor.Util.sortByArea(
    ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
)

// Get the largest blob
if (blobs.isNotEmpty()) {
    val largest = blobs[0]
    
    // Get position
    val box = largest.boxFit
    val x = box.center.x
    val y = box.center.y
    
    // Get properties
    val area = largest.contourArea
    val density = largest.density
    val aspectRatio = largest.aspectRatio
}

Builder Configuration

Target Color Range

Choose from predefined color ranges:

.setTargetColorRange(ColorRange.BLUE)
.setTargetColorRange(ColorRange.RED)
.setTargetColorRange(ColorRange.YELLOW)
.setTargetColorRange(ColorRange.GREEN)

Or define a custom range:

ColorRange customRange = new ColorRange(
    ColorSpace.YCrCb,                          // Color space
    new Scalar(0, 0, 150),                      // Lower bound
    new Scalar(255, 120, 255),                  // Upper bound
    ColorBlobLocatorProcessor.Scalar.RANGE_THRESHOLD  // Threshold
);

.setTargetColorRange(customRange)

Region of Interest (ROI)

Only process specific parts of the image:

// Entire frame
.setRoi(ImageRegion.entireFrame())

// Custom rectangle (x, y, width, height)
.setRoi(ImageRegion.asUnityCenterCoordinates(
    -0.5, -0.5,  // Top-left corner (-1 to 1)
    0.5, 0.5     // Bottom-right corner
))

// Pixel coordinates
ImageRegion customRoi = new ImageRegion() {
    @Override
    public Rect asImageCoordinates(int imageWidth, int imageHeight, 
                                   CameraCalibration calibration) {
        return new Rect(100, 100, 400, 300);  // x, y, width, height
    }
};
.setRoi(customRoi)

Contour Mode

Control which contours are detected:

// External contours only (default, fastest)
.setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)

// All contours (including holes)
.setContourMode(ColorBlobLocatorProcessor.ContourMode.ALL)

Visual Feedback

Draw detection results on the preview:

// Draw contours around detected blobs
.setDrawContours(true)

// Configure box drawing
.setBoxFit(ColorBlobLocatorProcessor.BoxFit.ROTATE)  // Rotated rectangle
.setBoxFit(ColorBlobLocatorProcessor.BoxFit.NONE)    // No box

Noise Reduction

Apply Gaussian blur to reduce noise:

// Blur size (odd number, 0 to disable)
.setBlurSize(5)  // 5x5 blur kernel

Higher values = more blur = less noise but also less detail.

Blob Properties

Each detected blob provides useful information:

Position Data

RotatedRect boxFit = blob.getBoxFit();

// Center position
double centerX = boxFit.center.x;
double centerY = boxFit.center.y;

// Box dimensions
double width = boxFit.size.width;
double height = boxFit.size.height;

// Rotation angle
double angle = boxFit.angle;

Shape Analysis

// Contour area (in pixels)
double area = blob.getContourArea();

// Density (how "filled" the blob is, 0-1)
double density = blob.getDensity();

// Aspect ratio (width / height)
double aspectRatio = blob.getAspectRatio();

// Bounding box
Rect boundingBox = blob.getContour().boundingRect();

Raw Contour

Access the raw OpenCV contour for advanced analysis:

MatOfPoint contour = blob.getContour();
// Use with OpenCV functions

Filtering and Sorting

Filter by Area

Keep only blobs within size range:

// Minimum pixels, maximum pixels
ColorBlobLocatorProcessor.Util.filterByArea(200, 5000, blobs);

Filter by Density

Keep only "solid" blobs:

// Minimum density (0.0 to 1.0)
ColorBlobLocatorProcessor.Util.filterByDensity(0.7, blobs);

Filter by Aspect Ratio

Keep only blobs with certain proportions:

// Minimum ratio, maximum ratio
ColorBlobLocatorProcessor.Util.filterByAspectRatio(0.5, 2.0, blobs);

Sort Blobs

// By area
ColorBlobLocatorProcessor.Util.sortByArea(SortOrder.DESCENDING, blobs);
ColorBlobLocatorProcessor.Util.sortByArea(SortOrder.ASCENDING, blobs);

// By density
ColorBlobLocatorProcessor.Util.sortByDensity(SortOrder.DESCENDING, blobs);

Complete Example: Team Prop Detection

This example detects a team prop and determines its position (left/center/right):

Java:

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import org.firstinspires.ftc.robotcore.external.hardware.camera.WebcamName;
import org.firstinspires.ftc.vision.VisionPortal;
import org.firstinspires.ftc.vision.opencv.ColorBlobLocatorProcessor;
import org.firstinspires.ftc.vision.opencv.ColorRange;
import org.firstinspires.ftc.vision.opencv.ImageRegion;
import org.opencv.core.RotatedRect;
import java.util.List;

@Autonomous(name = "Team Prop Detection")
public class TeamPropAuto extends LinearOpMode {
    
    enum PropPosition {
        LEFT,
        CENTER,
        RIGHT,
        NOT_FOUND
    }
    
    private VisionPortal visionPortal;
    private ColorBlobLocatorProcessor colorProcessor;
    
    @Override
    public void runOpMode() {
        
        // Create color processor for blue team prop
        colorProcessor = new ColorBlobLocatorProcessor.Builder()
            .setTargetColorRange(ColorRange.BLUE)
            .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
            .setRoi(ImageRegion.entireFrame())
            .setDrawContours(true)
            .setBlurSize(5)
            .build();
        
        // Create VisionPortal
        visionPortal = new VisionPortal.Builder()
            .setCamera(hardwareMap.get(WebcamName.class, "Webcam 1"))
            .addProcessor(colorProcessor)
            .build();
        
        // Wait for camera to start
        while (!isStarted() && !isStopRequested()) {
            PropPosition position = detectPropPosition();
            telemetry.addData("Prop Position", position);
            telemetry.addData("Status", "Ready! Press Play");
            telemetry.update();
            sleep(50);
        }
        
        // Get final position reading
        PropPosition finalPosition = detectPropPosition();
        
        // Disable processor to save resources
        visionPortal.setProcessorEnabled(colorProcessor, false);
        
        waitForStart();
        
        // Use detected position for autonomous
        switch (finalPosition) {
            case LEFT:
                telemetry.addLine("Going LEFT");
                // Execute left path
                break;
            case CENTER:
                telemetry.addLine("Going CENTER");
                // Execute center path
                break;
            case RIGHT:
                telemetry.addLine("Going RIGHT");
                // Execute right path
                break;
            case NOT_FOUND:
                telemetry.addLine("Prop not found, using default");
                // Execute default path
                break;
        }
        telemetry.update();
        
        sleep(2000);
        visionPortal.close();
    }
    
    private PropPosition detectPropPosition() {
        // Get detected blobs
        List<ColorBlobLocatorProcessor.Blob> blobs = colorProcessor.getBlobs();
        
        // Filter: area between 500-10000 pixels, density > 0.6
        ColorBlobLocatorProcessor.Util.filterByArea(500, 10000, blobs);
        ColorBlobLocatorProcessor.Util.filterByDensity(0.6, blobs);
        
        // Sort by size (largest first)
        ColorBlobLocatorProcessor.Util.sortByArea(
            ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
        );
        
        // Return position UNKNOWN if no blobs found
        if (blobs.isEmpty()) {
            return PropPosition.NOT_FOUND;
        }
        
        // Get largest blob
        ColorBlobLocatorProcessor.Blob largestBlob = blobs.get(0);
        RotatedRect boxFit = largestBlob.getBoxFit();
        double centerX = boxFit.center.x;
        
        // Determine position based on X coordinate
        // Assuming 640px wide image
        if (centerX < 213) {
            return PropPosition.LEFT;
        } else if (centerX < 427) {
            return PropPosition.CENTER;
        } else {
            return PropPosition.RIGHT;
        }
    }
}

Kotlin:

package org.firstinspires.ftc.teamcode

import com.qualcomm.robotcore.eventloop.opmode.Autonomous
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode
import org.firstinspires.ftc.robotcore.external.hardware.camera.WebcamName
import org.firstinspires.ftc.vision.VisionPortal
import org.firstinspires.ftc.vision.opencv.ColorBlobLocatorProcessor
import org.firstinspires.ftc.vision.opencv.ColorRange
import org.firstinspires.ftc.vision.opencv.ImageRegion

@Autonomous(name = "Team Prop Detection")
class TeamPropAuto : LinearOpMode() {
    
    enum class PropPosition {
        LEFT, CENTER, RIGHT, NOT_FOUND
    }
    
    private lateinit var visionPortal: VisionPortal
    private lateinit var colorProcessor: ColorBlobLocatorProcessor
    
    override fun runOpMode() {
        
        // Create color processor for blue team prop
        colorProcessor = ColorBlobLocatorProcessor.Builder()
            .setTargetColorRange(ColorRange.BLUE)
            .setContourMode(ColorBlobLocatorProcessor.ContourMode.EXTERNAL_ONLY)
            .setRoi(ImageRegion.entireFrame())
            .setDrawContours(true)
            .setBlurSize(5)
            .build()
        
        // Create VisionPortal
        visionPortal = VisionPortal.Builder()
            .setCamera(hardwareMap.get(WebcamName::class.java, "Webcam 1"))
            .addProcessor(colorProcessor)
            .build()
        
        // Wait for camera to start
        while (!isStarted && !isStopRequested) {
            val position = detectPropPosition()
            telemetry.addData("Prop Position", position)
            telemetry.addData("Status", "Ready! Press Play")
            telemetry.update()
            sleep(50)
        }
        
        // Get final position reading
        val finalPosition = detectPropPosition()
        
        // Disable processor to save resources
        visionPortal.setProcessorEnabled(colorProcessor, false)
        
        waitForStart()
        
        // Use detected position for autonomous
        when (finalPosition) {
            PropPosition.LEFT -> {
                telemetry.addLine("Going LEFT")
                // Execute left path
            }
            PropPosition.CENTER -> {
                telemetry.addLine("Going CENTER")
                // Execute center path
            }
            PropPosition.RIGHT -> {
                telemetry.addLine("Going RIGHT")
                // Execute right path
            }
            PropPosition.NOT_FOUND -> {
                telemetry.addLine("Prop not found, using default")
                // Execute default path
            }
        }
        telemetry.update()
        
        sleep(2000)
        visionPortal.close()
    }
    
    private fun detectPropPosition(): PropPosition {
        // Get detected blobs
        val blobs = colorProcessor.blobs
        
        // Filter: area between 500-10000 pixels, density > 0.6
        ColorBlobLocatorProcessor.Util.filterByArea(500.0, 10000.0, blobs)
        ColorBlobLocatorProcessor.Util.filterByDensity(0.6, blobs)
        
        // Sort by size (largest first)
        ColorBlobLocatorProcessor.Util.sortByArea(
            ColorBlobLocatorProcessor.Util.SortOrder.DESCENDING, blobs
        )
        
        // Return NOT_FOUND if no blobs found
        if (blobs.isEmpty()) {
            return PropPosition.NOT_FOUND
        }
        
        // Get largest blob
        val largestBlob = blobs[0]
        val boxFit = largestBlob.boxFit
        val centerX = boxFit.center.x
        
        // Determine position based on X coordinate
        // Assuming 640px wide image
        return when {
            centerX < 213 -> PropPosition.LEFT
            centerX < 427 -> PropPosition.CENTER
            else -> PropPosition.RIGHT
        }
    }
}

Tuning Tips

###1. Choose the Right Color Space

YCrCb - Best for FTC alliance colors (red/blue)
HSV - Good general-purpose choice
RGB - Least reliable, avoid if possible

2. Test Lighting Conditions

Tune parameters under:

Bright field lights
Dim lighting
With camera auto-exposure

3. Use Appropriate Filters

// Too restrictive: may miss objects
filterByArea(2000, 3000, blobs);  // Very narrow range
filterByDensity(0.95, blobs);      // Nearly perfect

// Just right: catches most cases
filterByArea(500, 5000, blobs);    // Reasonable range
filterByDensity(0.6, blobs);       // Allows imperfect detection

4. Handle Edge Cases

// Always check if blobs list is empty
if (!blobs.isEmpty()) {
    // Process blobs
} else {
    // Use default behavior
}

5. ROI for Performance

Limit search area to where objects appear:

// Only check bottom half of frame
.setRoi(ImageRegion.asUnityCenterCoordinates(-1, 0, 1, 1))

Troubleshooting

No Blobs Detected

Causes:

Wrong color range
Lighting too bright/dark
Object outside ROI
Filters too restrictive

Solutions:

Verify color range with EOCV-Sim
Adjust thresholds
Expand ROI
Loosen filters

Too Many False Positives

Causes:

Color range too broad
No area filtering
Similar colored background

Solutions:

Narrow color thresholds
Add filterByArea() and filterByDensity()
Use ROI to exclude background

Poor Performance

Causes:

High resolution
Large ROI
Complex scene

Solutions:

Reduce camera resolution
Restrict ROI
Increase blur size
Disable live view

Next Steps

Learn AprilTag Detection for precise localization
Create Custom VisionProcessors for advanced needs
See Integration Patterns for subsystem architecture

ColorBlobLocatorProcessor

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ColorBlobLocatorProcessor

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