Reading and displaying images in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read an image file named 'photo.jpg'.

MATLAB

img = [1]('photo.jpg');

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

Aimread

Bimshow

Cimwrite

Dimage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imshow' instead of 'imread' to load the image.

Using 'imwrite' which saves images, not reads them.

The imread function reads an image file into MATLAB.

2fill in blank

medium

Complete the code to display the image stored in variable 'img'.

MATLAB

[1](img);

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

Aimshow

Bimwrite

Cimage

Dimread

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imread' which reads images but does not display them.

Using 'image' which can display but is less common for images.

The imshow function displays an image stored in a variable.

3fill in blank

hard

Fix the error in the code to read and display 'picture.png'.

MATLAB

img = imread('picture.png');
[1](img);

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

Aimwrite

Bimage

Cimread

Dimshow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imwrite' which saves images instead of displaying.

Using 'imread' again instead of displaying.

After reading the image with imread, use imshow to display it.

4fill in blank

hard

Fill both blanks to read 'img.jpg' and display it with a title 'My Image'.

MATLAB

img = [1]('img.jpg');
[2](img);
title('My Image');

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

Aimread

Bimshow

Cimage

Dimwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imwrite' instead of 'imread' to load the image.

Using 'image' instead of 'imshow' to display.

Use imread to load the image and imshow to display it.

5fill in blank

hard

Fill all three blanks to read 'photo.tif', display it, and add axis labels.

MATLAB

img = [1]('photo.tif');
[2](img);
xlabel('[3]');

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

Aimread

Bimshow

CX Axis

Dimwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imwrite' instead of 'imread' to load the image.

Using 'image' instead of 'imshow' to display.

Forgetting to put the axis label as a string.

Use imread to read, imshow to display, and xlabel to label the x-axis.

Practice

1. What is the primary function of imread in MATLAB when working with images?

easy

A. To display an image on the screen

B. To save an image to a file

C. To load an image file into MATLAB as a matrix

D. To convert an image to grayscale

Solution

1. Step 1: Understand the purpose of imread

   imread reads image files and loads them into MATLAB as arrays (matrices) representing pixel data.

2. Step 2: Differentiate from other functions

   imshow displays images, imwrite saves images, and conversion functions change image formats. Only imread loads images.

3. Final Answer:

   To load an image file into MATLAB as a matrix -> Option C

4. Quick Check:

   imread = load image [OK]

Hint: Remember: 'read' means load data into MATLAB [OK]

Common Mistakes:

• Confusing imread with imshow
• Thinking imread displays images
• Assuming imread saves images

2. Which of the following is the correct syntax to display an image stored in variable img in MATLAB?

easy

A. imshow(img);

B. imread(img);

C. display(img);

D. show(img);

Solution

1. Step 1: Identify the function to display images

   imshow is the MATLAB function designed to show images stored in variables.

2. Step 2: Check syntax correctness

   The syntax imshow(img); correctly calls the function with the image variable.

3. Final Answer:

   imshow(img); -> Option A

4. Quick Check:

   Display image = imshow [OK]

Hint: Use imshow to show images, not imread [OK]

Common Mistakes:

• Using imread to display images
• Using non-existent functions like show
• Using display which does not render images

3. What will be the output of the following MATLAB code?

img = imread('peppers.png');
imshow(img);
size_img = size(img);

What does size_img contain?

medium

A. [384 512 3]

B. [512 384 3]

C. [384 512]

D. [512 384]

Solution

1. Step 1: Understand image dimensions

   The image 'peppers.png' is a color image with height 384 pixels, width 512 pixels, and 3 color channels (RGB).

2. Step 2: Interpret size output

   size(img) returns a vector with [rows, columns, color channels], so it is [384 512 3].

3. Final Answer:

   [384 512 3] -> Option A

4. Quick Check:

   Image size = [height width channels] = [384 512 3] [OK]

Hint: Remember size returns [rows columns channels] for images [OK]

Common Mistakes:

• Swapping width and height values
• Ignoring the third dimension for color channels
• Assuming grayscale image size format

4. Identify the error in the following MATLAB code snippet:

img = imread('flower.jpg')
imshow(img)

What is the likely cause if MATLAB throws an error?

medium

A. Missing semicolon after imread line

B. Variable img is not defined

C. Using imshow without parentheses

D. Incorrect file extension or file not found

Solution

1. Step 1: Check syntax correctness

   Missing semicolons do not cause errors, only suppress output. Parentheses are correctly used.

2. Step 2: Consider file-related errors

   If MATLAB cannot find 'flower.jpg' or the extension is wrong, imread throws an error.

3. Final Answer:

   Incorrect file extension or file not found -> Option D

4. Quick Check:

   File path/name errors cause imread failure [OK]

Hint: Check file name and path carefully if imread errors [OK]

Common Mistakes:

• Thinking missing semicolon causes error
• Assuming imshow syntax is wrong
• Ignoring file existence and path issues

5. You want to read an image and display only its red color channel in MATLAB. Which code snippet correctly achieves this?

hard

A. img = imread('image.png'); imshow(img(:,:,3));

B. img = imread('image.png'); imshow(img(:,:,1));

C. img = imread('image.png'); imshow(img(1,:,:));

D. img = imread('image.png'); imshow(img(:,1,:));

Solution

1. Step 1: Understand image color channels

   In MATLAB, the third dimension of an RGB image is color channels: 1=Red, 2=Green, 3=Blue.

2. Step 2: Extract and display red channel

   Using img(:,:,1) extracts the red channel matrix. Displaying it with imshow shows only red intensity.

3. Final Answer:

   img = imread('image.png'); imshow(img(:,:,1)); -> Option B

4. Quick Check:

   Red channel = third dimension index 1 [OK]

Hint: Use (:,:,1) to get red channel from RGB image [OK]

Common Mistakes:

• Using wrong channel index for red
• Trying to slice rows or columns incorrectly
• Confusing color channel order