Bounding box representation in Computer Vision - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a bounding box represented by its top-left corner and width and height.

Computer Vision

bbox = {'x': 50, 'y': 100, 'width': 200, 'height': [1]

Drag options to blanks, or click blank then click option'

A100

B250

C50

D150

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing width with height.

Using the x or y coordinate instead of height.

The height of the bounding box is 150 pixels, so we fill in the height value as 150.

2fill in blank

medium

Complete the code to calculate the bottom-right corner coordinates of the bounding box.

Computer Vision

bottom_right_x = bbox['x'] + [1]
bottom_right_y = bbox['y'] + bbox['height']

Drag options to blanks, or click blank then click option'

Abbox['x']

Bbbox['height']

Cbbox['width']

Dbbox['y']

Attempts:

3 left

💡 Hint

Common Mistakes

Adding height instead of width to x.

Adding y coordinate instead of width.

The bottom-right x coordinate is the top-left x plus the width of the bounding box.

3fill in blank

hard

Fix the error in the code to correctly compute the bounding box area.

Computer Vision

area = bbox['width'] [1] bbox['height']

Drag options to blanks, or click blank then click option'

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Adding width and height instead of multiplying.

Dividing width by height.

The area of a rectangle is width multiplied by height.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each bounding box id to its area.

Computer Vision

areas = {box_id: bbox[1] bbox[2] for box_id, bbox in boxes.items()}

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A['width'] *

B['height']

C['width'] +

D['height'] *

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Mixing up width and height keys.

We multiply the width and height values from each bounding box to get the area.

5fill in blank

hard

Fill all three blanks to create a function that converts bounding box from (x, y, width, height) to (x_min, y_min, x_max, y_max).

Computer Vision

def convert_bbox(bbox):
    x_min = bbox['x']
    y_min = bbox['y']
    x_max = bbox['x'] [1] bbox['width']
    y_max = bbox['y'] [2] bbox[[3]]
    return (x_min, y_min, x_max, y_max)

Drag options to blanks, or click blank then click option'

A+

B-

C'height'

D'width'

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting width or height instead of adding.

Using wrong keys for width or height.

To get x_max and y_max, add width to x and height to y respectively.

Practice

1. What does a bounding box represent in computer vision?

easy

A. The location of an object in an image using four numbers

B. The color of an object in an image

C. The texture pattern of an object

D. The size of the entire image

Solution

1. Step 1: Understand bounding box purpose

   A bounding box is used to locate objects visually in an image.

2. Step 2: Identify bounding box representation

   It uses four numbers to mark the top-left and bottom-right corners of the object.

3. Final Answer:

   The location of an object in an image using four numbers -> Option A

4. Quick Check:

   Bounding box = object location [OK]

Hint: Bounding box = 4 numbers marking object edges [OK]

Common Mistakes:

• Confusing bounding box with color or texture
• Thinking bounding box covers the whole image
• Believing bounding box uses only two numbers

2. Which of the following is the correct order of values in a bounding box representation?

easy

A. (bottom-left x, bottom-left y, top-right x, top-right y)

B. (center x, center y, width, height)

C. (width, height, top-left x, top-left y)

D. (top-left x, top-left y, bottom-right x, bottom-right y)

Solution

1. Step 1: Recall bounding box corner points

   The bounding box is defined by the top-left and bottom-right corners.

2. Step 2: Match the correct order

   The order is (top-left x, top-left y, bottom-right x, bottom-right y).

3. Final Answer:

   (top-left x, top-left y, bottom-right x, bottom-right y) -> Option D

4. Quick Check:

   Bounding box corners = top-left and bottom-right [OK]

Hint: Bounding box uses top-left then bottom-right coordinates [OK]

Common Mistakes:

• Mixing center coordinates with corner points
• Swapping bottom-left with top-left
• Using width and height before coordinates

3. Given a bounding box with coordinates (10, 20, 50, 80), what is the width and height of the box?

medium

A. Width = 40, Height = 60

B. Width = 60, Height = 40

C. Width = 50, Height = 80

D. Width = 30, Height = 50

Solution

1. Step 1: Calculate width from x-coordinates

   Width = bottom-right x - top-left x = 50 - 10 = 40.

2. Step 2: Calculate height from y-coordinates

   Height = bottom-right y - top-left y = 80 - 20 = 60.

3. Final Answer:

   Width = 40, Height = 60 -> Option A

4. Quick Check:

   Width = 50-10, Height = 80-20 [OK]

Hint: Width = x2 - x1, Height = y2 - y1 [OK]

Common Mistakes:

• Swapping width and height values
• Adding coordinates instead of subtracting
• Using top-left y for width calculation

4. Identify the error in this bounding box definition: bbox = (x1=30, y1=40, x2=20, y2=70)

medium

A. y2 should be less than y1

B. x2 is less than x1, which is invalid for bounding boxes

C. Coordinates must be strings, not integers

D. Bounding box must have five values, not four

Solution

1. Step 1: Check coordinate order validity

   Bounding box requires bottom-right x (x2) to be greater than top-left x (x1).

2. Step 2: Identify the error

   Here, x2=20 is less than x1=30, which is invalid and would cause errors in drawing or calculations.

3. Final Answer:

   x2 is less than x1, which is invalid for bounding boxes -> Option B

4. Quick Check:

   x2 must be > x1 for valid box [OK]

Hint: Bottom-right x must be greater than top-left x [OK]

Common Mistakes:

• Ignoring coordinate order rules
• Thinking y2 must be less than y1
• Assuming bounding box needs 5 values

5. You have bounding boxes in the format (center_x, center_y, width, height). How do you convert them to (top-left x, top-left y, bottom-right x, bottom-right y)?

hard

A. top-left x = center_x; top-left y = center_y; bottom-right x = width; bottom-right y = height

B. top-left x = center_x + width/2; top-left y = center_y + height/2; bottom-right x = center_x - width/2; bottom-right y = center_y - height/2

C. top-left x = center_x - width/2; top-left y = center_y - height/2; bottom-right x = center_x + width/2; bottom-right y = center_y + height/2

D. top-left x = width/2; top-left y = height/2; bottom-right x = center_x; bottom-right y = center_y

Solution

1. Step 1: Understand center to corner conversion

   Center coordinates are in the middle of the box; to get corners, subtract half width/height for top-left.

2. Step 2: Calculate corners from center and size

   Top-left x = center_x - width/2; top-left y = center_y - height/2; bottom-right x = center_x + width/2; bottom-right y = center_y + height/2.

3. Final Answer:

   top-left x = center_x - width/2; top-left y = center_y - height/2; bottom-right x = center_x + width/2; bottom-right y = center_y + height/2 -> Option C

4. Quick Check:

   Center ± half size = corners [OK]

Hint: Corners = center ± half width/height [OK]

Common Mistakes:

• Adding half width to top-left instead of subtracting
• Swapping top-left and bottom-right calculations
• Using width and height as coordinates directly