Data compression

Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.
Solidyne 922: The world's first commercial audio bit compression sound card for PC, 1990
Processing stages of a typical video encoder

Process of encoding information using fewer bits than the original representation.

- Data compression
Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.

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Alpha

A program in paper tape

Lossy compression

A program in paper tape

In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content.

Nasir Ahmed, the inventor of the discrete cosine transform (DCT), which he first proposed in 1972.

Discrete cosine transform

A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies.

A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies.

Nasir Ahmed, the inventor of the discrete cosine transform (DCT), which he first proposed in 1972.
Illustration of the implicit even/odd extensions of DCT input data, for N=11 data points (red dots), for the four most common types of DCT (types I-IV).
336x336px
An example showing eight different filters applied to a test image (top left) by multiplying its DCT spectrum (top right) with each filter.
Original size, scaled 10x (nearest neighbor), scaled 10x (bilinear).
Basis functions of the discrete cosine transformation with corresponding coefficients (specific for our image).
 DCT of the image =
.
On the left is the final image. In the middle is the weighted function (multiplied by a coefficient) which is added to the final image. On the right is the current function and corresponding coefficient. Images are scaled (using bilinear interpolation) by factor 10×.

The DCT, first proposed by Nasir Ahmed in 1972, is a widely used transformation technique in signal processing and data compression.

Comparison of coding efficiency between popular audio formats

MP3

Coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere.

Coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere.

Comparison of coding efficiency between popular audio formats

With regard to audio compression (the aspect of the standard most apparent to end-users, and for which it is best known), MP3 uses lossy data-compression to encode data using inexact approximations and the partial discarding of data.

Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.

Lossless compression

Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.

Lossless compression is a class of data compression that allows the original data to be perfectly reconstructed from the compressed data with no loss of information.

Advanced Video Coding

Video compression standard based on block-oriented, motion-compensated coding.

Video compression standard based on block-oriented, motion-compensated coding.

Block diagram of H.264
A YouTube video statistics with AVC (H.264) video codec and Opus audio format

AVC-Intra is an intraframe-only compression format, developed by Panasonic.

A photo of a European wildcat with the compression rate decreasing and hence quality increasing, from left to right

JPEG

Commonly used method of lossy compression for digital images, particularly for those images produced by digital photography.

Commonly used method of lossy compression for digital images, particularly for those images produced by digital photography.

A photo of a European wildcat with the compression rate decreasing and hence quality increasing, from left to right
The 8×8 sub-image shown in 8-bit grayscale
Zigzag ordering of JPEG image components
This image shows the pixels that are different between a non-compressed image and the same image JPEG compressed with a quality setting of 50. Darker means a larger difference. Note especially the changes occurring near sharp edges and having a block-like shape.
The original image
The compressed 8×8 squares are visible in the scaled-up picture, together with other visual artifacts of the lossy compression.
Visual impact of a jpeg compression on Photoshop on a picture of 4480x4480 pixels
An example of a stereoscopic .JPS file

In video compression MCUs are called macroblocks.

Comparison of coding efficiency between popular audio formats

Advanced Audio Coding

Comparison of coding efficiency between popular audio formats

Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression.

Comparison of JPEG images saved by Adobe Photoshop at different quality levels and with or without "save for web"

Image compression

Comparison of JPEG images saved by Adobe Photoshop at different quality levels and with or without "save for web"

Image compression is a type of data compression applied to digital images, to reduce their cost for storage or transmission.

Computer simulation, one of the main cross-computing methodologies.

Bit rate

Number of bits that are conveyed or processed per unit of time.

Number of bits that are conveyed or processed per unit of time.

Computer simulation, one of the main cross-computing methodologies.

It is sometimes higher than the physical layer data rate due to V.44 data compression, and sometimes lower due to bit-errors and automatic repeat request retransmissions.

MPEG-2 is used in Digital Video Broadcast and DVDs. The MPEG transport stream, TS, and MPEG program stream, PS, are container formats.

MPEG-2

Not to be confused with MPEG-1 Audio Layer II (MP2).

Not to be confused with MPEG-1 Audio Layer II (MP2).

MPEG-2 is used in Digital Video Broadcast and DVDs. The MPEG transport stream, TS, and MPEG program stream, PS, are container formats.

It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth.