title: Week 5 — Quiz ← Home · Student guide · Schedule · Weeks · Pseudocode · Glossary
Mini-Quiz (6–8 min) — Week 5: Representing Text & Images
Covers: ASCII, representing text, black & white images, color images (AP CSP, code.org Lessons 6–8)
#TODO Examples: JPEG, MP3, what information is lost. why/when/RAW format
Q1. What is ASCII and why is it important in computing?
Answer
ASCII (American Standard Code for Information Interchange) is a character encoding standard that assigns numbers to letters, digits, and symbols so computers can represent and process text.
Q2. What is the ASCII code for the letter ‘A’? What about ‘a’?
Answer
‘A’ = 65, ‘a’ = 97 (in decimal)
Q3. How can black and white images be represented in binary?
Answer
Each pixel is represented by a single bit: 0 for white, 1 for black (or vice versa). An image is a grid of these bits.
Q4. What is a pixel?
Answer
A pixel is the smallest unit of a digital image, representing a single point of color or shade.
Q5. How are color images typically represented in binary?
Answer
Each pixel is represented by three values (for Red, Green, Blue channels), with each value stored as a group of bits (often 8 bits per channel, so 24 bits per pixel).
Q6. What is the difference between a black & white image and a grayscale image in terms of binary representation?
Answer
Black & white images use 1 bit per pixel (2 possible values), while grayscale images use more bits per pixel (e.g., 8 bits for 256 shades of gray).
Q7. Why do computers use binary to represent images and text?
Answer
Computers use binary because their hardware is based on two states (on/off), making it efficient to store and process all types of data, including images and text, as sequences of 0s and 1s.
Q8. (Short answer) Give an example of a binary sequence and what text or image data it could represent.
Sample Answer
The binary sequence 01000001 represents the letter ‘A’ in ASCII. The sequence 11110000 could represent a row of 8 pixels in a black and white image (first 4 black, last 4 white).
Q9. What is a bitmap?
Answer
A bitmap is a way of representing an image as a grid of pixels, where each pixel’s value is stored in binary. For black and white images, each pixel is typically 1 bit.
Q10. How does increasing the number of bits per pixel affect an image?
Answer
Increasing the number of bits per pixel allows more colors or shades to be represented, resulting in higher image quality and detail.
Q11. What does RGB stand for, and how is it used in digital images?
Answer
RGB stands for Red, Green, Blue. In digital images, each pixel’s color is created by combining different intensities of these three colors, usually with 8 bits per channel.
Q12. Why might a RAW image file be much larger than a JPEG of the same photo?
Answer
RAW files store all the data captured by the camera sensor with little or no compression, while JPEG uses lossy compression to reduce file size by removing some data.
Q13. (Short answer) Give an example of how binary encoding is used to represent a simple black and white image.
Sample Answer
A 4x4 black and white image could be represented as: 1100 1010 0110 0001 where 1 = black, 0 = white.