Displaying images (cv2.imshow, matplotlib) in Computer Vision - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does cv2.imshow() do in image processing?

cv2.imshow() opens a window to display an image using OpenCV. It shows the image until a key is pressed.

beginner

How do you display an image using matplotlib?

Use plt.imshow() to show the image and plt.show() to display the window with the image.

intermediate

Why might images look different when displayed with cv2.imshow() vs matplotlib.pyplot.imshow()?

OpenCV uses BGR color order, while matplotlib uses RGB. Without converting colors, images may look strange in matplotlib.

beginner

What function is used to wait for a key press in OpenCV after showing an image?

cv2.waitKey() pauses the program and waits for a key press. It is needed to keep the image window open.

beginner

How do you close all OpenCV image windows programmatically?

Use cv2.destroyAllWindows() to close all windows opened by OpenCV.

Which function displays an image in a window using OpenCV?

A plt.showimage()

B plt.imshow()

C cv2.showimage()

D cv2.imshow()

cv2.imshow() is the correct OpenCV function to display images.

What must you call after cv2.imshow() to keep the window open until a key is pressed?

A cv2.waitKey()

B plt.show()

C cv2.destroyAllWindows()

D cv2.close()

cv2.waitKey() waits for a key press and keeps the window open.

Why do images sometimes appear with wrong colors in matplotlib after loading with OpenCV?

A OpenCV loads images in BGR format, matplotlib expects RGB

B Matplotlib cannot display color images

C OpenCV images are grayscale only

D Matplotlib requires images in grayscale

OpenCV uses BGR color order, so colors look wrong in matplotlib unless converted to RGB.

Which matplotlib function actually shows the image window?

A cv2.imshow()

B plt.show()

C plt.imshow()

D plt.display()

plt.show() displays the image window after plt.imshow() sets the image.

How do you close all OpenCV windows after displaying images?

A cv2.closeAll()

B plt.close()

C cv2.destroyAllWindows()

D cv2.closeWindows()

cv2.destroyAllWindows() closes all OpenCV image windows.

Explain how to display an image using OpenCV and keep the window open until a key is pressed.

Think about the functions needed to show and pause the image window.

Describe the difference in color formats between OpenCV and matplotlib and how to fix color issues when displaying images.

Consider how OpenCV loads colors and what matplotlib expects.