How images are stored (pixels, resolution) in Intro to Computing - Practice Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does image resolution represent?

Imagine a photo made of tiny colored squares called pixels. What does the resolution of an image tell us?

A The file size of the image in megabytes

B The number of pixels in width and height, showing image detail

C The number of colors used in the image

D The type of camera used to take the photo

💡 Hint

Think about how many tiny squares fit across and down the image.

Resolution means how many pixels are arranged horizontally and vertically. More pixels mean more detail.

❓ trace

intermediate

How many pixels in a 4x3 image?

Consider an image that is 4 pixels wide and 3 pixels tall. How many pixels does it have in total?

A 7 pixels

B 1 pixel

C 12 pixels

D 24 pixels

💡 Hint

Multiply width by height to find total pixels.

Total pixels = width × height = 4 × 3 = 12 pixels.

❓ Comparison

advanced

Comparing image quality by resolution

Two images have these resolutions:
Image 1: 800x600 pixels
Image 2: 1600x1200 pixels
Which image will generally have better detail?

A Image 2 because it has four times more pixels

B Image 1 because it has fewer pixels

C Both have the same detail because they are rectangular

D Image 1 because it loads faster

💡 Hint

Think about total pixels and how that affects detail.

Image 2 has 1600×1200 = 1,920,000 pixels, which is four times Image 1's 480,000 pixels, so it shows more detail.

❓ identification

advanced

Identify the pixel arrangement in an image

Which diagram best represents a 3x3 pixel image where each square is a pixel?

Options:

• A: A grid with 3 rows and 3 columns of squares
• B: A grid with 2 rows and 3 columns of squares
• C: A grid with 3 rows and 2 columns of squares
• D: A single row with 9 squares

A 3 rows and 2 columns forming 6 pixels

B 2 rows and 3 columns forming 6 pixels

C 1 row and 9 columns forming 9 pixels

D 3 rows and 3 columns forming 9 pixels

💡 Hint

Count rows and columns to match 3x3 pixels.

A 3x3 pixel image has 3 rows and 3 columns, making 9 pixels total.

🚀 Application

expert

Calculate file size from image resolution and color depth

An image has a resolution of 1000x500 pixels. Each pixel uses 24 bits (3 bytes) to store color. What is the approximate file size in bytes (ignore compression)?

A 1,500,000 bytes

B 1,000,000 bytes

C 15,000,000 bytes

D 500,000 bytes

💡 Hint

Multiply total pixels by bytes per pixel.

Total pixels = 1000 × 500 = 500,000 pixels.
Each pixel = 3 bytes.
File size = 500,000 × 3 = 1,500,000 bytes (A).

Practice

1. What is a pixel in a digital image?

easy

A. A tiny dot that makes up the image

B. A type of file format

C. A color filter used in cameras

D. A tool to edit images

Solution

1. Step 1: Understand the basic unit of an image

   An image is made up of many small dots called pixels.

2. Step 2: Identify what a pixel represents

   A pixel is the smallest part of an image that holds color information.

3. Final Answer:

   A tiny dot that makes up the image -> Option A

4. Quick Check:

   Pixel = tiny dot [OK]

Hint: Pixels are tiny dots forming the image [OK]

Common Mistakes:

• Confusing pixels with file formats
• Thinking pixels are editing tools
• Mixing pixels with camera filters

2. Which of the following correctly describes image resolution?

easy

A. The size of the image file in megabytes

B. The color depth of the image

C. The number of pixels in width and height

D. The type of camera used to take the image

Solution

1. Step 1: Define resolution in terms of pixels

   Resolution means how many pixels are arranged horizontally and vertically.

2. Step 2: Differentiate resolution from file size and color depth

   File size and color depth are different properties; resolution is about pixel count.

3. Final Answer:

   The number of pixels in width and height -> Option C

4. Quick Check:

   Resolution = pixel count width x height [OK]

Hint: Resolution counts pixels horizontally and vertically [OK]

Common Mistakes:

• Confusing resolution with file size
• Mixing resolution with color depth
• Thinking resolution depends on camera type

3. An image has a resolution of 1920 x 1080 pixels. How many pixels does it contain in total?

medium

A. 1920 pixels

B. 200,000 pixels

C. 1080 pixels

D. 2,073,600 pixels

Solution

1. Step 1: Multiply width and height pixels

   Total pixels = 1920 (width) x 1080 (height) = 2,073,600 pixels.

2. Step 2: Confirm calculation

   Multiplying these gives the total number of pixels in the image.

3. Final Answer:

   2,073,600 pixels -> Option D

4. Quick Check:

   1920 x 1080 = 2,073,600 [OK]

Hint: Multiply width by height for total pixels [OK]

Common Mistakes:

• Adding instead of multiplying width and height
• Confusing width or height as total pixels
• Ignoring the multiplication step

4. A student says an image with resolution 800 x 600 has 1400 pixels. What is wrong with this statement?

medium

A. They confused pixels with file size

B. They added width and height instead of multiplying

C. They multiplied width and height correctly

D. They used the wrong units for pixels

Solution

1. Step 1: Calculate correct total pixels

   Total pixels = 800 x 600 = 480,000 pixels, not 1400.

2. Step 2: Identify mistake in calculation

   1400 is close to 800 + 600 = 1400, so they added instead of multiplied.

3. Final Answer:

   They added width and height instead of multiplying -> Option B

4. Quick Check:

   Pixels = width x height, not addition [OK]

Hint: Pixels = width x height, not width + height [OK]

Common Mistakes:

• Adding instead of multiplying pixels
• Confusing pixels with file size
• Misunderstanding resolution units

5. If you double the resolution of an image from 640 x 480 to 1280 x 960, how does the total number of pixels change?

hard

A. It quadruples

B. It stays the same

C. It doubles

D. It halves

Solution

1. Step 1: Calculate original total pixels

   Original pixels = 640 x 480 = 307,200 pixels.

2. Step 2: Calculate new total pixels

   New pixels = 1280 x 960 = 1,228,800 pixels.

3. Step 3: Compare new and original pixels

   1,228,800 ÷ 307,200 = 4, so total pixels quadruple.

4. Final Answer:

   It quadruples -> Option A

5. Quick Check:

   Doubling width and height quadruples pixels [OK]

Hint: Doubling width & height quadruples pixels [OK]

Common Mistakes:

• Thinking doubling resolution doubles pixels
• Ignoring multiplication effect on total pixels
• Confusing resolution with file size