1.3 Compression
AS Level · 17 questions found
What this topic covers
Section titled “What this topic covers”- Need for compression and examples of its use
- Lossy vs lossless compression; justify which to use for a given situation
- How text, bitmap, vector and sound files can be compressed
- Run-length encoding (RLE)
Past paper questions
Section titled “Past paper questions”(a) A sound file is compressed by reducing the sampling rate. 1 mark
State whether this is lossless or lossy compression. Justify your choice.
Type of compression
Justification
(b) The following table shows some words and corresponding denary values. 1 mark
| Word | Denary value |
|---|---|
| Computing | 55 |
| Science | 56 |
| Computers | 57 |
| are | 58 |
| Brilliant! | 59 |
| is | 60 |
| Fun! | 61 |
| Amazing! | 62 |
The following table shows three bytes of data that have been received.
Use the table to find the corresponding words from the binary values received.
| Binary value | 00111000 | 00111100 | 00111110 |
|---|---|---|---|
| Word |
Working
(c) A computer system uses even parity. The least significant (rightmost) bit of each byte is the parity bit.
(i) Complete the byte by writing the missing parity bit: 1 mark
parity bit
(ii) The computer also uses parity block check. The parity block check uses even parity.
Computer A transmits four bytes of data to computer B, followed by a parity byte. Computer B receives the following sequence of bytes.
parity bit
| 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 |
|---|---|---|---|---|---|---|---|
| 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 1 | 0 | 1 | 1 |
| 0 | 1 | 1 | 1 | 0 | 1 | 0 | 0 |
| 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
Following transmission, one of the four bytes of data has an error in one of the bits.
Circle the bit that has been altered during the data transfer. [1]
(d) A bitmap image has a resolution of 1000 pixels wide by 2000 pixels high. The colour depth is 16 bits. 2 marks
Calculate an estimate of the file size in megabytes.
Show your working.
File size ______ megabytes
Show mark scheme
6(a) [1 mark]
1 mark for correct answer Type of compression: lossy Justification: There will be fewer samples per second, so data will be permanently lost // There will be fewer samples per second, so the original sound cannot be re- created
6(b) [1 mark]
1 mark for correct words in the correct order Binary Value 0011 1000 0011 1100 0011 1110 Word Science is Amazing!
6(c)(i) [1 mark]
1 mark for correct answer parity bit ↓ 0 1 0 1 1 1 0 0
6(c)(ii) [1 mark]
1 mark for correct answer parity bit ↓ 1 0 1 1 0 1 1 1 0 0 1 1 1 0 0 0 0 0 0 1 1 0 1 1 0 1 1 1 0 1 0 0 parity byte→ 1 0 1 0 0 0 0 0 [1]
6(d) [2 marks]
1 mark for the working 1 mark for the correct answer Working: (1000 * 2000 * 16) / (8 * 1000 * 1000) // (1000 * 2000 * 2 / (1000 * 1000) Answer: 4 megabytes
Programmers in a software development company take part in live video conferences to discuss their work.
The live video conferences take place using real‑time bit streaming. The video is compressed before it is transmitted.
(a) Explain how data is transferred using real‑time bit streaming. 4 marks
(b) (i) Explain the reasons why a video is compressed before it is transmitted using real‑time bit streaming. 4 marks
Show mark scheme
2(a) [4 marks]
1 mark each to max 4 • Video is transmitted continuously • as a series of bits • The video is uploaded to a media server • The users download from the media server • On download, the media server sends the data to a buffer on the user's device • buffer is used when there is a difference in speed between transmission and receipt • Buffer stores data from server until recipient can receive it • Recipient views bit stream from the buffer
2(b)(i) [4 marks]
1 mark each to max 4 e.g. • Video is data-intensive • The file size needs reducing in order to • reduce the amount of bandwidth used • and reduce buffering • This means people are not behind in the conversation • and people with lower bandwidth can still take part
2(b)(ii) [3 marks]
No mark for choice but lossy is most appropriate 1 mark each to max 3 e.g. • Reduces file size more than lossless • so significantly less bandwidth / data is needed • so buffering is reduced even more than with lossless • Data can be removed which cannot be seen • reducing quality without impacting experience • for example, because resolution of video can be reduced // sample rate of audio can be reduced
2(c) [2 marks]
1 mark each modems: • Converts digital data into analogue for transmission down phone lines // Converts analogue data into digital after transmission down phone lines dedicated lines: • Used to provide a direct / private connection which therefore provides faster transmission
A computer stores images and text files.
Show mark scheme
3(a) [3 marks]
1 mark for each correct answer Statement The term for the smallest element that pixel makes up an image. 8 The largest number of different colours that 256 // 2 can be represented with a bit depth of 8 bits. The term for the dots per inch (dpi) when an Screen resolution image is displayed.
3(b)(i) [2 marks]
1 mark each to max 2 • A wider range of characters can be represented • so characters from more languages can be represented • and symbols such as emojis can be used
3(b)(ii) [1 mark]
1 mark for: 10,094
3(b)(iii) [1 mark]
1 mark for: 8,512
A student uses a laptop to write a program that is saved as a text file.
(a) The laptop has utility software and an Operating System (OS).
(i) Describe the file management tasks carried out by an OS. 2 marks
(ii) Explain the need for back-up software. 2 marks
(b) The student compresses the file before it is emailed to their teacher as an attachment.
(i) Explain the benefits to the teacher of the attachment being a compressed file. 3 marks
(ii) Describe one lossless method of compressing a text file. 3 marks
(c) The student used a program library when writing their program. 3 marks
Explain the benefits to the student of using library files when writing a program.
(d) The program code is written using an Integrated Development Environment (IDE).
(i) One presentation feature found in a typical IDE is prettyprint. 2 marks
Identify and describe one other presentation feature found in a typical IDE.
Feature
Description
(ii) One debugging feature found in a typical IDE is single stepping. 2 marks
Identify and describe one other debugging feature found in a typical IDE.
Feature
Description
Show mark scheme
4(a)(i) [2 marks]
1 mark for each bullet point ( max 2 ) e.g. • Secondary storage space is divided into file allocation units • Space on secondary storage is allocated to particular files • Maintains/creates directory structures • Specifies the logical method of file storage e.g. FAT or NTFS • Provides file naming conventions • Controls user access // implements access rights //implements password protection // Makes file sharing possible • Controls access to the file by other software • Specifies tasks that can be performed on a file e.g. open, close, delete, copy, create, move, etc • Allows searching for a file
4(a)(ii) [2 marks]
1 mark for each bullet point ( max 2 ) • To allow data to be retrieved / restored when lost • To automatically make a duplicate copy of data… • …so the user does not have to remember to backup data • To make regular duplicate copies of data
4(b)(i) [3 marks]
1 mark for each bullet point ( max 3 ) e.g. • Less of the teacher’s storage space is used • ... so more student work can be stored • Transmission time is reduced • … so the teacher does not have to wait as long for it to arrive • Bandwidth usage is reduced • … so other transmissions are not adversely affected • Less data allowance is used on the teacher’s email system
4(b)(ii) [3 marks]
1 mark for each bullet point ( max 3 ) • Run-Length Encoding // RLE • Repeated sequences of the same characters are replaced by • ... a single copy of the character • ... and a count of the number of characters
4(c) [3 marks]
1 mark for each bullet point ( max 3 ) e.g. • It saves development time for the student • … by using pre-written code • There is less testing to do // the routines are more likely to work correctly • … because they have already been tested and are error-free • It results in a more robust program • Subroutines can be used that they do not have the skill to write • … which enables a more complex program to be written
4(d)(i) [2 marks]
1 mark for correct name, 1 mark for matching description • Expand/collapse code blocks… • … sections of source code that are part of the same block can be expanded to see the content or collapsed so that the overall code is seen • Auto-indentation // auto-formatting... • ... automatically indents/formats code as the user types so that the structure is clear // aids readability
4(d)(ii) [2 marks]
1 mark for correct name, 1 mark for matching description • Breakpoints … • … stops the code running on a set line to view the current status/variable contents/program flow • Report window // variable watch window … • … shows the values in variables/data structures and how they change when each line is run
A student takes a photograph of a science experiment.
(a) The photograph is saved as a bitmapped image.
(i) Define the following bitmap terms. 2 marks
Colour depth
File header
(ii) Explain why changing the image resolution will affect the image quality and file size. 2 marks
Image quality
File size
(iii) Identify one lossless method of compressing an image. 1 mark
(b) The student draws a picture on paper that is scanned into the computer and saved as a vector graphic. 2 marks
Define the vector graphic terms property and drawing list.
Property
Drawing list
Show mark scheme
7(a)(i) [2 marks]
1 mark for each correct definition Colour depth: • the number of bits used to represent a colour // the number of colours that can be represented in an image File header: • stores data about the image file / metadata
7(a)(ii) [2 marks]
1 mark for each correct explanation Image quality: • Decreasing resolution means details within the image are lost because there are fewer pixels // Increasing resolution means the image is more detailed because there are more pixels File size: • Decreasing the resolution will decrease the file size because there are fewer pixels therefore less data // Increasing the resolution will increase the file size because there are more pixels therefore more data
7(a)(iii) [1 mark]
1 mark for correct method For example: • Run-Length Encoding
7(b) [2 marks]
1 mark for each correct definition Property: • an attribute of a drawing object // data about a shape // defines one aspect of the appearance of a drawing object Drawing list: • all the drawing objects/shapes in an image // stores the commands/descriptions / mathematical equations required to draw each object
A computer system stores text, images and sound.
(a) A character set is used to represent characters in a computer. 2 marks
Identify and describe one character set.
Character set
Description
(b) The colour of each pixel in a bitmapped image is represented by 8 bits.
(i) State the largest number of different colours that can be represented by 8 bits. 1 mark
(ii) State one drawback of increasing the number of bits that represents each pixel in the bitmap image. 1 mark
(iii) A bitmap image can be compressed using lossy compression. 2 marks
Explain the reasons why lossy compression is often suitable for a bitmap image.
(c) (i) Explain how an analogue sound wave is converted into digital data. 2 marks
(ii) Describe one method of compressing a sound file using lossy compression. 2 marks
Show mark scheme
6(a) [2 marks]
1 mark for identification 1 mark for matching description e.g. • ASCII • 7/8 bits per character // represents 128/256 characters // represents all characters from Latin alphabet • UNICODE • 8/16/32 bits per character // represents 256/65536+ characters // represents all characters in all languages
6(b)(i) [1 mark]
1 mark for: 256 // 2 8
6(b)(ii) [1 mark]
1 mark for: Increased file size
6(b)(iii) [2 marks]
1 mark for each bullet point ( max 2 ) e.g. • The change may not be noticeable // Data removed is usually not noticed by the human eye • … for example, changes in shade/detail • It produces a larger decrease in file size compared to lossless // Lossy decreases file size considerably
6(c)(i) [2 marks]
1 mark for each bullet point ( max 2 ) • Value magnitude/size of the analogue sound wave is measured a set / number of times each second/time / at set intervals • Each sample/reading/measurement is given the binary number and stored in sequence
6(c)(ii) [2 marks]
1 mark for each correct point and 1 mark for matching expansion e.g. • Decrease sample rate • … fewer samples/readings/measurements stored per second // fewer bits per second stored • Decrease sample resolution • … fewer bits per sample/reading/measurement // each sample has fewer bits • Sound outside of set/human hearing range is removed • … fewer measurements are stored / decreases the number of possible binary values so fewer bits are stored
(a) Draw one line from each vector graphic term to its most appropriate description. 2 marks
Term
drawing list
Description
a component created using a formula
defines one characteristic drawing object of a component
data required to create all property components in the graphic
(b) State what is meant by the bit depth of a bitmap image and explain how changing the bit depth affects the image. 3 marks
Definition
Explanation
(c) Explain why a bitmap image is often compressed before it is attached to an email. 2 marks
Show mark scheme
1(a) [2 marks]
2 marks for all 3 lines correct 1 mark for 1 line correct Description Term a component created drawing list using a formula defines one characteristic drawing object of a component data required to create all property components in the graphic
1(b) [3 marks]
1 mark for the definition • The number of bits used to represent each colour 1 mark for each bullet point for the explanation • Increase in bit depth means the image has a greater range of colours // Decrease in bit depth means the image has a smaller range of colours • Increase in bit depth makes the image closer to the original / more realistic // Decrease in bit depth makes the image less like the original / less realistic
1(c) [2 marks]
1 mark for each bullet point ( max 2 ) • Reduced bandwidth usage when transmitting the message • Reduced transmission time from email client to email server • Reduced storage space on the email • Email accounts often have a maximum size for an attachment
(a) A real-time video of a music concert needs to be streamed to subscribers. 3 marks
| Tick (✓) one b | box to identify |
|---|---|
| Lossy | Lossless |
Justification
(b) Explain the impact of changing the sampling resolution on the accuracy of a sound recording. 3 marks
(c) A bitmap image has a resolution of 2048 pixels wide and 1024 pixels high. 2 marks
The image has a bit depth of 10 bits per pixel.
Estimate the file size of the bitmap image in mebibytes. Show your working.
Working
Estimated file size in mebibytes
Show mark scheme
6(a) [3 marks]
1 mark for each bullet point ( max 3 ) Lossy compression (ticked) • Loss of quality will not be noticed • Needs to be viewed in real time so less bandwidth needed if file size smaller • Smaller file sizes will reduce buffering so the video will play more smoothly • Viewers may watch on different devices, so may not need high quality resolution Lossless compression (ticked) • Original recording may not have been made in high resolution • Could be streaming to high bandwidth devices • The reduction in the file size is sufficient for the receiving device • Viewers do not want any loss of quality
6(b) [3 marks]
1 mark for each bullet point ( max 3 ) Increase sampling resolution • … the number of bits used for each sample is increased • … there will be more values available to represent each sample // more amplitudes can be represented • ... each binary amplitude/note in the digital recording is closer to the analogue amplitude/note • … quantisation errors are reduced • … the digital soundwave is closer to the original analogue soundwave Decrease sampling resolution • … the number of bits used for each sample is decreased • … there will be fewer values available to represent each sample // fewer amplitudes can be stored • ... each binary amplitude/note in the digital recording is further from the analogue amplitude/note • … quantisation errors are increased • … the digital soundwave is less like the original analogue soundwave
6(c) [2 marks]
1 mark for answer, 1 mark for working Answer: 2.5 mebibytes Working: (2048 1024 10) / (8 1024 1024)
A programmer uses an Integrated Development Environment (IDE) to develop a program that monitors air quality.
(a) Describe the following features of a typical IDE. 4 marks
Context‑sensitive prompts
Single stepping
(b) The program is distributed by downloading the source code and its library files from a web server.
(i) Explain the reasons for compressing the files. 2 marks
(ii) The program files are stored on a new hard disk after they have been downloaded. 3 marks
Describe the reasons why a hard disk formatter is needed for the new hard disk.
Show mark scheme
5(a) [4 marks]
1 mark for each bullet point ( max 2 for each feature). Context-sensitive prompts: • As the code is being written • …the options to complete the statement are shown Single stepping: • allows the programmer to execute the program one line at a time • …so that the effects of each statement can be seen
5(b)(i) [2 marks]
1 mark for each bullet point ( max 2 ). • To reduce the time it takes to download the program files from the web server // to upload them to the server in the first place • To reduce the amount of storage space used on the web server // user’s device
5(b)(ii) [3 marks]
1 mark for each bullet point ( max 3 ). • Disk needs to be prepared for initial use • Disk needs to be checked for errors • A new file system needs to be generated on the disk • The file allocation table needs to be set up
A Local Area Network (LAN) consists of four computers, one server and a switch.
The LAN uses a star topology.
(a) Complete the following diagram to show how the hardware is connected. 1 mark
Computer Computer Server Computer Computer
(b) A router is attached to one of the devices on the LAN shown in part (a) to connect the LAN to the internet.
(i) Identify the device. Give a reason for your choice. 2 marks
Device
Reason
(ii) Describe the role and function of the router in the network. 3 marks
Show mark scheme
10(a) [1 mark]
all four computers directly connected to the switch and no other connections.
10(b)(i) [2 marks]
1 mark for the device. 1 mark for corresponding reason. • Device: Server • Reason: Server processes the requests and authorises traffic // firewall software on the server authorises traffic // server acts as the proxy • Device: Switch • Reason: Switch is connected to all the computers // to share access to the router on the network
10(b)(ii) [3 marks]
1 mark for each bullet point (max 3) : • receive packets from devices / internet • find destination of packets using the IP address • forward packets to the destination • assign private IP addresses to devices on LAN • store/update/maintain a routing table • find most efficient path to destination • maintain table of MAC and IP addresses • provides the LAN with a public IP address • acts as a gateway • performs protocol conversion • acts as a firewall
Show mark scheme
10(a) [3 marks]
1 mark for each bullet point: • to ensure the system operates with the given criteria • ... by enabling system output to affect subsequent system input • ... thus allowing conditions to be automatically adjusted
10(b)(i) [2 marks]
1 mark for identification of a suitable sensor 1 mark for corresponding justification Example: • sound sensor • if a sound occurs inside the car the alarm is activated • infra-red sensor • senses the heat of person in the car / infra-red beams are broken • pressure sensor • an intruder sits in the driver’s seat
10(b)(ii) [3 marks]
1 mark for each bullet point ( max 3 ): • the embedded system is built into / integrated (into the car alarm) • combination of hardware and software designed for a specific function • must have a processor, memory and input / output • The system is not easily changed /updated by the car owner
Text and numbers are examples of data stored in a computer.
(a) A character set is used to represent characters in a computer.
(i) Describe what is meant by a character set . 2 marks
(ii) Identify two character sets and state one difference between them. 3 marks
Character set 1
Character set 2
Difference
(iii) Describe how lossless compression can be used to reduce the file size of a text file. 2 marks
(iv) Explain why lossy compression should not be used on a text file. 2 marks
Show mark scheme
1(a)(i)
1 mark per point to max 2 All of the characters/symbols that the computer can use/represent Each character has a unique number/binary number/hexadecimal number
1(a)(ii) [3 marks]
1 mark for each character set to max 2 , 1 mark for difference ASCII Extended ASCII UNICODE ASCII has 7 bits whereas UNICODE has 16 bits Extended ASCII has 8 bits whereas UNICODE has 16 bits ASCII has 7 bits whereas extended ASCII has 8 bits Unicode can represent more characters than ASCII/Extended// by example Extended ASCII can represent more characters than ASCII
1(a)(iii) [2 marks]
1 mark per point to max 2 Can use run-length encoding Identifies groups of repeated characters ... ... replaces them with a one copy of the character and the number of times it occurs
1(a)(iv) [2 marks]
1 mark per point to max 2 None of the original data can be lost / deleted The (text) file would be corrupted // the (text) file cannot be opened
1(b) [5 marks]
1 mark for each correct value Statement The hexadecimal value 11 represented in denary 17 The smallest denary number that be represented by an 0 unsigned 8-bit binary integer The denary number 87 represented in Binary Coded 1000 0111 Decimal (BCD) The denary number 240 represented in hexadecimal F0 The denary number –20 represented in 8-bit two’s 1110 1100 complement binary
Bobby is recording a sound file for his school project.
(a) He repeats the recording of the sound several times, with a different sample rate each time.
(i) Describe the reasons why the sound is closer to the original when a higher sample rate is used. 2 marks
(ii) Describe the reasons why the sound file size increases when a higher sample rate is used. 2 marks
(b) Bobby wants to email the sound file to his school email address. He compresses the file before sending the email.
(i) Explain the reasons why Bobby compresses the sound file. 2 marks
(ii) Bobby uses lossless compression. 2 marks
Describe how lossless compression can compress the sound file.
Show mark scheme
7(a)(i) [2 marks]
1 mark per bullet point Smaller time gaps between the samples • Makes the digital sound wave more accurate • Smaller quantisation errors •
7(a)(ii)
1 mark per bullet point More samples/data are taken/recorded • … so more bits are stored altogether •
7(b)(i) [2 marks]
1 mark per bullet point Reduces the file size • Faster to transmit/download • Original file is too large for email storage/attachment •
7(b)(ii) [2 marks]
1 mark per bullet point to max 2 e.g. Reduce amplitude to only the range used • … limited amplitudes mean fewer bits per sample • Run-length-encoding • … Where consecutive sounds are the same record the binary value of the • sound and number of times it repeats Record the changes instead of the actual sounds •
Riya has created the following logo as a vector graphic.
| R | ||
(a) Complete the table by writing a description of each vector graphic term and give an example for this logo. 4 marks
| Term | Description | Example from logo |
|---|---|---|
| Property | ||
| Drawing list |
(b) Riya takes a photograph using a digital camera. The photograph is stored as a bitmap image.
(i) Describe two differences between a vector graphic and a bitmap image. 4 marks
1
2
(ii) Riya needs to email the photograph. She compresses the photograph before sending it using an email. 4 marks
Describe two lossy methods that Riya can use to compress the image.
Method 1
Method 2
Show mark scheme
5(a) [4 marks]
1 mark for each description, 1 mark for each valid example Term Description Example from logo e.g. data about the shapes black line // white fill // black fill // defines one aspect of the Property //solid (line) // font of letter // appearance of the drawing colour of triangle object e.g. the list of shapes involved in triangle // capital letter R // an image Drawing rectangle // line // a list that stores the list command/description required to draw each object
5(b)(i) [4 marks]
1 mark for each bullet point to max 2 for each difference Bitmap made up of pixels // bitmap is made of colours stored for • individual pixels Vector graphic store a set of instructions about how to draw the shape • When bitmap is enlarged the pixels get bigger and it pixelates • When vector is enlarged it is recalculated and does not pixelate • Bitmap files are usually bigger than vector graphics files because of the • need to store data about each pixel Vector graphics have smaller file size because they contain just the • instructions to create the shapes Bitmap images can be compressed with significant reduction in file size • Vector graphic images do not compress well because of little redundant • data
5(b)(ii) [4 marks]
1 mark for each bullet point to max 2 for each method Reduce bit depth • ... reduces the number of bits per colour / pixel which means each pixel • has fewer bits Reduce colour palette // reduce number of colours • ... fewer colours mean fewer bits needed to store each colour • Reduce image resolution • ... fewer pixels per unit measurement means less binary to store •
Bobby is recording a sound file for his school project.
(a) He repeats the recording of the sound several times, with a different sample rate each time.
(i) Describe the reasons why the sound is closer to the original when a higher sample rate is used. 2 marks
(ii) Describe the reasons why the sound file size increases when a higher sample rate is used. 2 marks
(b) Bobby wants to email the sound file to his school email address. He compresses the file before sending the email.
(i) Explain the reasons why Bobby compresses the sound file. 2 marks
(ii) Bobby uses lossless compression. 2 marks
Describe how lossless compression can compress the sound file.
Show mark scheme
7(a)(i) [2 marks]
1 mark per bullet point Smaller time gaps between the samples • Makes the digital sound wave more accurate • Smaller quantisation errors •
7(a)(ii)
1 mark per bullet point More samples/data are taken/recorded • … so more bits are stored altogether •
7(b)(i) [2 marks]
1 mark per bullet point Reduces the file size • Faster to transmit/download • Original file is too large for email storage/attachment •
7(b)(ii) [2 marks]
1 mark per bullet point to max 2 e.g. Reduce amplitude to only the range used • … limited amplitudes mean fewer bits per sample • Run-length-encoding • … Where consecutive sounds are the same record the binary value of the • sound and number of times it repeats Record the changes instead of the actual sounds •
Anya scans an image into her computer for a school project.
(a) The scanned image is a bitmapped image. 2 marks
| (i) Com | mplete the following table to describe the two terms about graphics. |
|---|---|
| Term | Description |
| Pixel | ______ |
| File header | ______ |
(ii) The image is scanned with an image resolution of 1024 × 512 pixels, and a colour depth of 8 bits per pixel. 3 marks
Calculate an estimate for the file size, giving your answer in mebibytes. Show your working.
Working
Answer ______ mebibytes
(b) The image is compressed using lossless compression. 3 marks
Identify one method of lossless compression that can be used to compress the image and describe how the method will reduce the file size.
Lossless compression method
Description
Show mark scheme
1(a)(i) [3 marks]
1 mark for each description Pixel: A single square of one colour • The smallest addressable element in an image • File header: Data about the bitmap image (e.g. number of colours) •
1(a)(ii) [3 marks]
1 mark per bullet point for working, 1 mark for answer Working: 1024 512 = 524 288 pixels/bytes • × 524288 / 1024 / 1024 • Answer: 0.50 mebibytes
1(b)
1 mark for naming method, 1 mark per description to max 2 Run-length encoding • Replace sequences of the same colour pixel • … with colour code and number of identical pixels •
1(c)(i) [1 mark]
252
1(c)(ii) [3 marks]
1 mark per bullet point Converting 15 to binary • 0000 1111 Method for addition • Final answer • 0010 0011
- 0000 1111 0011 0010 1 111
1(c)(iii) [3 marks]
1 mark per bullet point Converting −10 to two's complement binary • 1111 0110 Adding values • Final answer • 0001 1001 10 = 0000 1010 –10 = 1111 0110 0010 0011
- 1111 0110 0001 1001 11 11
1(d) [2 marks]
1 mark per bullet point to max 2 The formal and legal rights to ownership // intellectual property rights • Protects against unauthorised reproduction of work • Provides for legal right of redress •
Anya scans an image into her computer for a school project.
(a) The scanned image is a bitmapped image. 2 marks
| (i) Com | mplete the following table to describe the two terms about graphics. |
|---|---|
| Term | Description |
| Pixel | ______ |
| File header | ______ |
(ii) The image is scanned with an image resolution of 1024 × 512 pixels, and a colour depth of 8 bits per pixel. 3 marks
Calculate an estimate for the file size, giving your answer in mebibytes. Show your working.
Working
Answer ______ mebibytes
(b) The image is compressed using lossless compression. 3 marks
Identify one method of lossless compression that can be used to compress the image and describe how the method will reduce the file size.
Lossless compression method
Description
Show mark scheme
1(a)(i) [3 marks]
1 mark for each description Pixel: A single square of one colour • The smallest addressable element in an image • File header: Data about the bitmap image (e.g. number of colours) •
1(a)(ii) [3 marks]
1 mark per bullet point for working, 1 mark for answer Working: 1024 512 = 524 288 pixels/bytes • × 524288 / 1024 / 1024 • Answer: 0.50 mebibytes
1(b)
1 mark for naming method, 1 mark per description to max 2 Run-length encoding • Replace sequences of the same colour pixel • … with colour code and number of identical pixels •
1(c)(i) [1 mark]
252
1(c)(ii) [3 marks]
1 mark per bullet point Converting 15 to binary • 0000 1111 Method for addition • Final answer • 0010 0011
- 0000 1111 0011 0010 1 111
1(c)(iii) [3 marks]
1 mark per bullet point Converting −10 to two's complement binary • 1111 0110 Adding values • Final answer • 0001 1001 10 = 0000 1010 –10 = 1111 0110 0010 0011
- 1111 0110 0001 1001 11 11
1(d) [2 marks]
1 mark per bullet point to max 2 The formal and legal rights to ownership // intellectual property rights • Protects against unauthorised reproduction of work • Provides for legal right of redress •