85. AQA GCSE (8525) SLR13 – 3.3 Compression Run length encoding

What compression technique is typically used to compress text-based data?

• JPEG compression

• LZW compression

• Huffman coding

• Run length encoding

Answer explanation

Huffman coding is typically used to compress text-based data by assigning shorter codes to more frequent characters, reducing the overall size of the data.

What is run length encoding typically used to compress?

• Audio files

• Video files

• Text-based data

• Bitmap images

Answer explanation

Run length encoding is typically used to compress bitmap images by reducing redundancy in consecutive pixels of the same color.

How many bits are used to encode each pixel in a simple black-and-white bitmap image?

• 2 bits

• 4 bits

• 8 bits

• 1 bit

Answer explanation

Each pixel in a simple black-and-white bitmap image is encoded using 1 bit, representing either black or white. Therefore, 1 bit is used to encode each pixel.

What does a '0' represent in the context of encoding a black-and-white bitmap image?

• A black pixel

• An error

• A white pixel

• A transparent pixel

Answer explanation

In the context of encoding a black-and-white bitmap image, a '0' represents a white pixel.

How many bits of information would be needed to store a sequence of 100 pixels without compression?

• 25 bits

• 200 bits

• 50 bits

• 100 bits

Answer explanation

To store 100 pixels without compression, each pixel requires 1 bit of information. Therefore, 100 pixels would need 100 bits of information.

What are frequency data pairs used for in run length encoding?

• To encode audio frequencies

• To encrypt data

• To represent the length and color of pixel sequences

• To compress text files

Answer explanation

Frequency data pairs are used in run length encoding to represent the length and color of pixel sequences, not for encoding audio frequencies, encrypting data, or compressing text files.

In the example given, how many white pixels are followed by 6 black pixels?

• 6 white pixels

• 8 white pixels

• 1 white pixel

• 22 white pixels

Answer explanation

In the example, 22 white pixels are followed by 6 black pixels, making the correct answer choice 22 white pixels.

What does the number '22' represent in the frequency data pair '22, 0'?

• 22 errors

• 22 white pixels

• 22 bits

• 22 black pixels

Answer explanation

The number '22' represents 22 white pixels in the frequency data pair '22, 0'.

What assumption is made about the colors used in the bitmap image?

• It uses a color depth of 8 bits

• It only contains red and blue pixels

• It uses just black and white pixels

• It contains multiple colors

Answer explanation

The correct assumption made about the colors used in the bitmap image is that it uses just black and white pixels.

What does a '1' represent in the context of encoding a black-and-white bitmap image?

• An error

• A black pixel

• A white pixel

• A transparent pixel

Answer explanation

In the context of encoding a black-and-white bitmap image, a '1' represents a black pixel. Therefore, the correct choice is 'A black pixel'.