Multimedia Technology Lecture 7: Lossy Compression Algorithms

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Questions and Answers

What is the most common type of multimedia compression algorithm?

Lossless compression

Dynamic compression

Lossy compression (correct)

Adaptive compression

What is the main characteristic of lossy compression?

Requires more storage space than lossless compression

Is slower than lossless compression

Produces an exact replica of the original data

Yields a much higher compression ratio than lossless compression (correct)

Which compression method is commonly used for digital images?

TIFF

GIF

PNG

JPEG (correct)

What is the degree of compression typically achieved by JPEG for digital images?

10:1 Signup and view all the answers

What does distortion refer to in the context of multimedia compression?

The amount of error introduced by lossy compression Signup and view all the answers

Which type of compression allows for a selectable tradeoff between storage size and image quality?

Lossy compression Signup and view all the answers

What is the formula for mean square error (MSE) in image compression?

σ^2 = (Σ (xn - yn)^2) / N Signup and view all the answers

Which measure is most commonly used to assess the quality of reconstruction of lossy compression codecs in image compression?

Peak signal to noise ratio (PSNR) Signup and view all the answers

What are typical PSNR values for lossy image and video compression with 8-bit data?

30-50 dB Signup and view all the answers

In which domain do we deal with the rate at which pixel values are changing?

Frequency domain Signup and view all the answers

Why is Discrete Cosine Transform (DCT) considered a better representation for image data in frequency domain?

It allows you to separate and discard unimportant information based on human perception sensitivity Signup and view all the answers

What is the rationale behind transform coding using Discrete Cosine Transform (DCT)?

Components of Y are much less correlated, making Y more efficiently coded than X Signup and view all the answers

What does PSNR stand for in image compression?

Peak Signal to Noise Ratio Signup and view all the answers

What is the average square value of the original data sequence in SNR calculation?

(Σ x^2) / N Signup and view all the answers

What does MSE stand for in image compression?

Mean Square Error Signup and view all the answers

What do typical PSNR values indicate for lossy image and video compression with 16-bit data?

60-80 dB Signup and view all the answers

Study Notes

Multimedia Compression

The most common type of multimedia compression algorithm is lossy compression.

Characteristics of Lossy Compression

The main characteristic of lossy compression is that it discards some of the data, resulting in a loss of quality.

Image Compression

JPEG (Joint Photographic Experts Group) is commonly used for digital images.
JPEG typically achieves a compression ratio of 10:1 to 20:1 for digital images.

Distortion and Compression

Distortion refers to the difference between the original and reconstructed data after compression.

Selectable Compression

Transform coding allows for a selectable tradeoff between storage size and image quality.

Mean Square Error (MSE)

The formula for MSE in image compression is: MSE = (1/N) * Σ(xi - yi)^2, where xi is the original data and yi is the reconstructed data.

Quality Assessment

Peak Signal-to-Noise Ratio (PSNR) is the most commonly used measure to assess the quality of reconstruction of lossy compression codecs in image compression.

PSNR Values

Typical PSNR values for lossy image and video compression with 8-bit data are 30-40 dB.
Typical PSNR values for lossy image and video compression with 16-bit data are 40-50 dB.

Frequency Domain

The frequency domain is where we deal with the rate at which pixel values are changing.

Discrete Cosine Transform (DCT)

DCT is considered a better representation for image data in the frequency domain because it is more efficient and effective in representing the spatial frequencies of an image.
The rationale behind transform coding using DCT is that it takes advantage of the fact that most of the image's energy is concentrated in the lower frequencies.

PSNR and MSE

PSNR stands for Peak Signal-to-Noise Ratio in image compression.
MSE stands for Mean Square Error in image compression.
The average square value of the original data sequence in SNR (Signal-to-Noise Ratio) calculation is the signal power.

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Description

This lecture discusses lossy compression algorithms in multimedia technology, covering the concept of lossy compression and its implications on data. The presentation is prepared by Assoc. Prof. Dr Hossam Mahmoud Moftah from the Faculty of Computers and Artificial Intelligence at Beni-Suef University.