Drawing on images (lines, rectangles, circles, text) in Computer Vision - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to draw a blue line on the image.

Computer Vision

import cv2
import numpy as np

img = np.zeros((200, 200, 3), dtype=np.uint8)
cv2.line(img, (10, 10), (190, 10), [1], 3)
cv2.imwrite('line.png', img)

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

A(0, 0, 255)

B(255, 0, 0)

C(255, 255, 0)

D(0, 255, 0)

Attempts:

3 left

💡 Hint

Common Mistakes

Using RGB color instead of BGR.

Confusing blue with red color values.

OpenCV uses BGR color format. Blue is (255, 0, 0), which is option B. Option B (0, 0, 255) is red.

2fill in blank

medium

Complete the code to draw a filled green rectangle on the image.

Computer Vision

import cv2
import numpy as np

img = np.zeros((200, 200, 3), dtype=np.uint8)
cv2.rectangle(img, (50, 50), (150, 150), [1], -1)
cv2.imwrite('rectangle.png', img)

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

A(0, 255, 255)

B(0, 0, 255)

C(255, 0, 0)

D(0, 255, 0)

Attempts:

3 left

💡 Hint

Common Mistakes

Using RGB color instead of BGR.

Using positive thickness instead of -1 for filled shapes.

The color green in OpenCV BGR format is (0, 255, 0). The thickness -1 fills the rectangle.

3fill in blank

hard

Fix the error in the code to draw a red circle on the image.

Computer Vision

import cv2
import numpy as np

img = np.zeros((200, 200, 3), dtype=np.uint8)
cv2.circle(img, (100, 100), 50, [1], 5)
cv2.imwrite('circle.png', img)

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

A(0, 0, 255)

B(255, 0, 0)

C(0, 255, 0)

D(255, 255, 255)

Attempts:

3 left

💡 Hint

Common Mistakes

Using RGB color instead of BGR.

Using wrong color tuple causing unexpected colors.

The color red in OpenCV BGR format is (0, 0, 255). The code uses this color to draw the circle.

4fill in blank

hard

Fill both blanks to draw white text on the image at position (50, 180).

Computer Vision

import cv2
import numpy as np

img = np.zeros((200, 200, 3), dtype=np.uint8)
cv2.putText(img, 'Hello', (50, 180), [1], 1, [2], 2)
cv2.imwrite('text.png', img)

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

Acv2.FONT_HERSHEY_SIMPLEX

B(255, 255, 255)

C(0, 0, 0)

Dcv2.LINE_AA

Attempts:

3 left

💡 Hint

Common Mistakes

Using black color instead of white for text.

Using invalid font constants.

The font cv2.FONT_HERSHEY_SIMPLEX is a common readable font. The color white in BGR is (255, 255, 255).

5fill in blank

hard

Fill all three blanks to draw a green circle with thickness 3 and anti-aliased line.

Computer Vision

import cv2
import numpy as np

img = np.zeros((300, 300, 3), dtype=np.uint8)
cv2.circle(img, (150, 150), 75, [1], [2], [3])
cv2.imwrite('circle_aa.png', img)

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

A(0, 255, 0)

B3

Ccv2.LINE_AA

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong color format.

Using thickness 5 instead of 3.

Omitting anti-aliasing flag.

The green color is (0, 255, 0). Thickness is 3 pixels. cv2.LINE_AA enables smooth anti-aliased edges.