Why computer vision teaches machines to see - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load an image using OpenCV.

Computer Vision

import cv2
image = cv2.[1]('image.jpg')

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

Aimread

Bimwrite

Cimshow

Dresize

Attempts:

3 left

💡 Hint

Common Mistakes

Using imshow instead of imread will display an image, not load it.

The cv2.imread function reads an image from a file into a matrix that the computer can process.

2fill in blank

medium

Complete the code to convert the image to grayscale.

Computer Vision

gray_image = cv2.cvtColor(image, [1])

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Acv2.COLOR_BGR2GRAY

Bcv2.COLOR_RGB2BGR

Ccv2.COLOR_GRAY2BGR

Dcv2.COLOR_BGR2RGB

Attempts:

3 left

💡 Hint

Common Mistakes

Using COLOR_BGR2RGB changes color format but not to grayscale.

cv2.COLOR_BGR2GRAY converts a color image to grayscale, which simplifies the image for many computer vision tasks.

3fill in blank

hard

Fix the error in the code to detect edges using Canny.

Computer Vision

edges = cv2.Canny(image, [1], 150)

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

A'50'

B50

CNone

Dimage

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string '50' causes a type error.

The first threshold for the Canny edge detector should be a number, like 50, not a string or None.

4fill in blank

hard

Fill both blanks to create a dictionary of pixel intensities for pixels greater than 100.

Computer Vision

pixel_dict = { (x, y): image[x, y] for x in range(image.shape[[1]]) for y in range(image.shape[[2]]) if image[x, y] > 100 }

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

A0

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up width and height indices.

In an image array, shape[0] is height (rows) and shape[1] is width (columns).

5fill in blank

hard

Fill all three blanks to create a dictionary of pixel intensities for pixels with intensity above 120 in grayscale image.

Computer Vision

bright_pixels = { ([1], [2]): gray_image[[1], [2]] for [1] in range(gray_image.shape[0]) for [2] in range(gray_image.shape[1]) if gray_image[[1], [2]] > 120 }

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

Ax

By

Cz

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables inconsistently causes errors.

We use variables x and y to loop over rows and columns. The first blank is x, second is y, and the third repeats x to index the image.

Practice

1. What is the main goal of computer vision in machines?

easy

A. To store large amounts of data

B. To help machines understand and interpret images and videos

C. To make machines run faster

D. To improve battery life of devices

Solution

1. Step 1: Understand the purpose of computer vision

   Computer vision is about teaching machines to see and understand visual data like images and videos.

2. Step 2: Identify the correct goal

   The goal is not about speed, storage, or battery but about interpreting visual information.

3. Final Answer:

   To help machines understand and interpret images and videos -> Option B

4. Quick Check:

   Computer vision = understanding images/videos [OK]

Hint: Think: What does 'vision' mean for machines? [OK]

Common Mistakes:

• Confusing computer vision with hardware improvements
• Thinking it only stores data
• Mixing vision with battery or speed

2. Which of the following is the correct way to represent an image as data for a machine to process?

easy

A. A single number

B. A list of text descriptions

C. A matrix of pixel values

D. A sound wave

Solution

1. Step 1: Recall how images are stored digitally

   Images are stored as grids of pixels, each with color or brightness values, forming a matrix.

2. Step 2: Match the correct representation

   Only a matrix of pixel values correctly represents image data for machines.

3. Final Answer:

   A matrix of pixel values -> Option C

4. Quick Check:

   Image data = pixel matrix [OK]

Hint: Images = grids of pixels, not text or sound [OK]

Common Mistakes:

• Choosing text descriptions instead of pixel data
• Thinking images are single numbers
• Confusing images with sounds

3. Given the following Python code snippet for edge detection, what will be the output shape of edges if the input image shape is (100, 100)?

import cv2
image = cv2.imread('photo.jpg', 0)
edges = cv2.Canny(image, 100, 200)
print(edges.shape)

medium

A. (50, 50)

B. (98, 98)

C. (102, 102)

D. (100, 100)

Solution

1. Step 1: Understand Canny edge detection output size

   Canny edge detection returns an image of the same size as the input image.

2. Step 2: Check input image shape

   The input image shape is (100, 100), so the output edges will also have shape (100, 100).

3. Final Answer:

   (100, 100) -> Option D

4. Quick Check:

   Canny output shape = input shape [OK]

Hint: Edge detection keeps image size same [OK]

Common Mistakes:

• Assuming edges shrink image size
• Thinking edges enlarge image
• Confusing shape with number of edges

4. The following code is intended to convert an image to grayscale using OpenCV. What is the error?

import cv2
image = cv2.imread('photo.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
cv2.imshow('Gray Image', gray)
cv2.waitKey(0)
cv2.destroyAllWindows()

medium

A. No error, code works correctly

B. cv2.imread should include flag cv2.IMREAD_GRAYSCALE

C. cv2.cvtColor is used incorrectly

D. Missing image file path

Solution

1. Step 1: Check image reading method

   cv2.imread reads the image in color by default, which is fine for conversion.

2. Step 2: Verify color conversion usage

   cv2.cvtColor with cv2.COLOR_BGR2GRAY correctly converts color image to grayscale.

3. Step 3: Confirm display functions

   cv2.imshow, cv2.waitKey, and cv2.destroyAllWindows are used properly to show the image.

4. Final Answer:

   No error, code works correctly -> Option A

5. Quick Check:

   Correct grayscale conversion code [OK]

Hint: cv2.cvtColor with COLOR_BGR2GRAY is standard [OK]

Common Mistakes:

• Thinking cv2.imread needs grayscale flag always
• Misusing cv2.cvtColor parameters
• Forgetting to call cv2.waitKey

5. You want to teach a machine to recognize handwritten digits using computer vision. Which combination of steps is best to prepare the images before training a model?

hard

A. Convert images to grayscale, normalize pixel values, and detect edges

B. Convert images to color, increase brightness, and add noise

C. Resize images to large size, convert to text, and shuffle pixels

D. Use raw images without any processing

Solution

1. Step 1: Identify useful preprocessing steps for digit recognition

   Converting to grayscale simplifies data, normalizing scales pixel values, and edge detection highlights important features.

2. Step 2: Evaluate other options

   Color conversion and noise addition can confuse the model; resizing too large or converting to text is not helpful; raw images may have noise and irrelevant info.

3. Final Answer:

   Convert images to grayscale, normalize pixel values, and detect edges -> Option A

4. Quick Check:

   Preprocessing = grayscale + normalize + edges [OK]

Hint: Simplify images and highlight features before training [OK]

Common Mistakes:

• Using color images unnecessarily
• Adding noise that confuses model
• Skipping normalization
• Ignoring edge detection benefits