Color-based tracking in Drone Programming - Step-by-Step Execution

Concept Flow - Color-based tracking

Start Camera

↓

Capture Frame

↓

Detect Color Pixels

↓

Calculate Object Position

↓

Adjust Drone Movement

↓

Repeat or Stop

The drone camera captures frames, detects pixels of a target color, calculates the object's position, and moves accordingly in a loop.

Execution Sample

Drone Programming

frame = camera.capture()
color_mask = detect_color(frame, target_color)
position = find_object_position(color_mask)
drone.move_towards(position)

This code captures a frame, finds the target color pixels, calculates the object's position, and moves the drone toward it.

Execution Table

Step	Action	Input	Output	Drone Movement
1	Capture Frame	Camera active	Image frame with colors	Hover
2	Detect Color Pixels	Image frame, target_color=red	Mask highlighting red pixels	Hover
3	Calculate Object Position	Color mask	Coordinates (x=150, y=100)	Hover
4	Adjust Drone Movement	Coordinates (150,100)	Movement command: move right and forward	Moves right and forward
5	Capture Frame	Camera active	New image frame	Moves right and forward
6	Detect Color Pixels	New frame, target_color=red	Mask highlighting red pixels	Moves right and forward
7	Calculate Object Position	New color mask	Coordinates (x=160, y=110)	Moves right and forward
8	Adjust Drone Movement	Coordinates (160,110)	Movement command: move right and forward	Moves right and forward
9	Repeat or Stop	User input or condition	Continue tracking or stop	Continue or hover

💡 Tracking stops when user commands or target color is lost

Variable Tracker

Variable	Start	After Step 3	After Step 7	Final
frame	None	Image frame 1	Image frame 2	Image frame N
color_mask	None	Mask of red pixels 1	Mask of red pixels 2	Mask of red pixels N
position	None	(150, 100)	(160, 110)	(xN, yN)
drone_movement	Hover	Moves right and forward	Moves right and forward	Hover or move

Key Moments - 2 Insights

Why does the drone keep moving even if the color position changes slightly?

Because each new frame updates the position and the drone adjusts movement accordingly, as shown in steps 3, 4, 7, and 8 in the execution_table.

What happens if the target color is not detected in a frame?

The color_mask will be empty, so the position cannot be calculated, and the drone will hover or stop, as implied in the exit_note.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the position output?

A (150, 100)

B (160, 110)

C No position

D (0, 0)

💡 Hint

Check the 'Output' column at step 3 in the execution_table.

At which step does the drone first move right and forward?

A Step 2

B Step 1

C Step 4

D Step 9

💡 Hint

Look at the 'Drone Movement' column in the execution_table.

If the color_mask is empty, what will the drone most likely do?

A Move right

B Hover or stop

C Move forward

D Move backward

💡 Hint

Refer to the key_moments and exit_note about what happens when the target color is lost.

Concept Snapshot

Color-based tracking uses the drone camera to capture frames.
It detects pixels matching a target color.
Calculates the object's position from these pixels.
Drone moves toward the detected position.
This repeats continuously to follow the object.

Full Transcript

Color-based tracking works by the drone camera capturing images continuously. Each image is checked for pixels of a specific color. When these pixels are found, the program calculates where the object is in the frame. The drone then moves in the direction of the object to follow it. This process repeats, allowing the drone to track the colored object in real time. If the color is lost or the user stops the program, the drone will hover or stop moving.

Practice

1. What is the main purpose of color-based tracking in drone programming?

easy

A. To make the drone follow an object by detecting its color

B. To control the drone's altitude using GPS

C. To improve the drone's battery life

D. To send commands to the drone via remote control

Solution

1. Step 1: Understand color-based tracking concept

   Color-based tracking means the drone uses color detection to follow an object.

2. Step 2: Identify the main goal

   The goal is to detect and follow an object by its color, not altitude or battery.

3. Final Answer:

   To make the drone follow an object by detecting its color -> Option A

4. Quick Check:

   Color-based tracking = follow object by color [OK]

Hint: Focus on color detection as the tracking method [OK]

Common Mistakes:

• Confusing color tracking with GPS control
• Thinking it manages battery or remote commands
• Mixing color tracking with altitude control

2. Which of the following code snippets correctly initializes a color filter for red in a drone's tracking system?

easy

A. red_filter = {'lower': (0, 255, 255), 'upper': (10, 100, 100)}

B. red_filter = {'lower': [100, 0, 0], 'upper': [255, 10, 10]}

C. red_filter = {'low': (0, 100, 100), 'high': (10, 255, 255)}

D. red_filter = {'lower': (0, 100, 100), 'upper': (10, 255, 255)}

Solution

1. Step 1: Check correct keys for filter dictionary

   The keys should be 'lower' and 'upper' to define color range.

2. Step 2: Verify value types and ranges

   Values must be tuples with HSV ranges; red_filter = {'lower': (0, 100, 100), 'upper': (10, 255, 255)} uses correct keys and tuples.

3. Final Answer:

   red_filter = {'lower': (0, 100, 100), 'upper': (10, 255, 255)} -> Option D

4. Quick Check:

   Correct keys and tuple values = red_filter = {'lower': (0, 100, 100), 'upper': (10, 255, 255)} [OK]

Hint: Look for 'lower' and 'upper' keys with tuple HSV values [OK]

Common Mistakes:

• Using wrong dictionary keys like 'low' or 'high'
• Using lists instead of tuples for HSV values
• Swapping lower and upper HSV ranges

3. Given the following code snippet for detecting a blue object, what will be printed if the detected object's center is at (150, 200)?

blue_filter = {'lower': (100, 150, 0), 'upper': (140, 255, 255)}
object_center = (150, 200)
if 100 <= object_center[0] <= 140:
    print('Blue object detected at', object_center)
else:
    print('No blue object detected')

medium

A. Blue object detected at (150, 200)

B. SyntaxError

C. No blue object detected

D. RuntimeError

Solution

1. Step 1: Check the condition on x-coordinate

   Condition checks if 100 <= 150 <= 140, which is false because 150 > 140.

2. Step 2: Determine which print executes

   Since condition is false, else block runs printing 'No blue object detected'.

3. Final Answer:

   No blue object detected -> Option C

4. Quick Check:

   150 not in 100-140 range = No detection [OK]

Hint: Check numeric range conditions carefully [OK]

Common Mistakes:

• Assuming 150 is within 100 to 140 range
• Confusing syntax errors with logic errors
• Ignoring else block output

4. The following code is intended to detect a green object and print its position, but it raises an error. What is the error and how to fix it?

green_filter = {'lower': (40, 50, 50), 'upper': (80, 255, 255)}
object_center = None
if green_filter['lower'][0] <= object_center[0] <= green_filter['upper'][0]:
    print('Green object at', object_center)
else:
    print('No green object detected')

medium

A. SyntaxError due to incorrect dictionary keys; fix keys to 'low' and 'high'

B. TypeError because object_center is None; fix by assigning a tuple to object_center

C. IndexError because green_filter keys are missing; add keys

D. No error; code runs correctly

Solution

1. Step 1: Identify the error cause

   object_center is None, so accessing object_center[0] causes TypeError.

2. Step 2: Fix the error

   Assign a tuple like (x, y) to object_center before using it in condition.

3. Final Answer:

   TypeError because object_center is None; fix by assigning a tuple to object_center -> Option B

4. Quick Check:

   None used as index causes TypeError [OK]

Hint: Check variable types before indexing [OK]

Common Mistakes:

• Ignoring NoneType indexing error
• Changing dictionary keys incorrectly
• Assuming code runs without error

5. You want the drone to follow a yellow object but only if its detected center's y-coordinate is above 100. Which code snippet correctly implements this condition using color-based tracking?

yellow_filter = {'lower': (20, 100, 100), 'upper': (30, 255, 255)}
object_center = (120, 150)

# Choose the correct condition to check

hard

A. if yellow_filter['lower'][0] <= object_center[0] <= yellow_filter['upper'][0] and object_center[1] > 100:
print('Following yellow object')

B. if yellow_filter['lower'][1] <= object_center[1] <= yellow_filter['upper'][1] and object_center[0] > 100:
print('Following yellow object')

C. if yellow_filter['lower'][0] <= object_center[1] <= yellow_filter['upper'][0] and object_center[0] > 100:
print('Following yellow object')

D. if yellow_filter['lower'][1] <= object_center[0] <= yellow_filter['upper'][1] and object_center[1] > 100:
print('Following yellow object')

Solution

1. Step 1: Understand HSV and coordinate roles

   yellow_filter keys 'lower' and 'upper' define hue range at index 0; object_center[0] is x, object_center[1] is y.

2. Step 2: Check condition for hue and y-coordinate

   Hue check uses object_center[0] between lower and upper hue; y-coordinate must be > 100.

3. Final Answer:

   if yellow_filter['lower'][0] <= object_center[0] <= yellow_filter['upper'][0] and object_center[1] > 100: print('Following yellow object') -> Option A

4. Quick Check:

   Hue range on x and y > 100 condition = if yellow_filter['lower'][0] <= object_center[0] <= yellow_filter['upper'][0] and object_center[1] > 100: print('Following yellow object') [OK]

Hint: Match hue with x, check y > 100 separately [OK]

Common Mistakes:

• Mixing x and y coordinates in conditions
• Using wrong indices for hue or saturation
• Checking y-coordinate against hue range