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.

84 related topics

Alpha

Sequitur algorithm

Recursive algorithm developed by Craig Nevill-Manning and Ian H. Witten in 1997 that infers a hierarchical structure (context-free grammar) from a sequence of discrete symbols.

Recursive algorithm developed by Craig Nevill-Manning and Ian H. Witten in 1997 that infers a hierarchical structure (context-free grammar) from a sequence of discrete symbols.

It can be used in data compression software applications.

Strings are often made up of characters. They are useful for storing human-readable data, like sentences, or lists of alphabetical data, like the nucleic acid sequences of DNA.

Burrows–Wheeler transform

The Burrows–Wheeler transform (BWT, also called block-sorting compression) rearranges a character string into runs of similar characters.

The Burrows–Wheeler transform (BWT, also called block-sorting compression) rearranges a character string into runs of similar characters.

Strings are often made up of characters. They are useful for storing human-readable data, like sentences, or lists of alphabetical data, like the nucleic acid sequences of DNA.

The Burrows–Wheeler transform is an algorithm used to prepare data for use with data compression techniques such as bzip2.

Some of the different types of data.

Data communication

Transfer and reception of data in the form of a digital bitstream or a digitized analog signal over a point-to-point or point-to-multipoint communication channel.

Transfer and reception of data in the form of a digital bitstream or a digitized analog signal over a point-to-point or point-to-multipoint communication channel.

Some of the different types of data.

It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream, for example, using pulse-code modulation or more advanced source coding schemes.

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.

Block Diagram of HEVC

High Efficiency Video Coding

Video compression standard designed as part of the MPEG-H project as a successor to the widely used Advanced Video Coding (AVC, H.264, or MPEG-4 Part 10).

Video compression standard designed as part of the MPEG-H project as a successor to the widely used Advanced Video Coding (AVC, H.264, or MPEG-4 Part 10).

Block Diagram of HEVC
HEVC has 33 intra prediction modes

In comparison to AVC, HEVC offers from 25% to 50% better data compression at the same level of video quality, or substantially improved video quality at the same bit rate.

A humorous image announcing the launch of a Tumblr account for the White House suggests pronouncing GIF with a hard g.

GIF

Bitmap image format that was developed by a team at the online services provider CompuServe led by American computer scientist Steve Wilhite and released on 15 June 1987.

Bitmap image format that was developed by a team at the online services provider CompuServe led by American computer scientist Steve Wilhite and released on 15 June 1987.

A humorous image announcing the launch of a Tumblr account for the White House suggests pronouncing GIF with a hard g.
An example of a GIF image saved with a web-safe palette and dithered using the Floyd–Steinberg method. Due to the reduced number of colors in the image, there are display issues.
An animated GIF illustrating a technique for displaying more than the typical limit of 256 colors
Sample image (enlarged), actual size 3 pixels wide by 5 high
Bytes Dh to 30Ch in the example define a palette of 256 colors.
A 46×46 uncompressed GIF with 7-bit symbols (128 colors, 8-bit codes). Click on the image for an explanation of the code.
GIF can be used to display animation, as in this image of Newton's cradle.
A GIF animation made of two photos, one morphing into the other
Rotating earth (large).gif

GIF became popular because it used Lempel–Ziv–Welch 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.

Transform coding

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.

Transform coding is a type of data compression for "natural" data like audio signals or photographic images.

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.

Face detection process

Human visual system model

Used by image processing, video processing and computer vision experts to deal with biological and psychological processes that are not yet fully understood.

Used by image processing, video processing and computer vision experts to deal with biological and psychological processes that are not yet fully understood.

Face detection process

Similar concepts are applied in audio compression, where sound frequencies inaudible to humans are bandstop filtered.

Nasir Ahmed in 2012

Nasir Ahmed (engineer)

Indian and American electrical engineer and computer scientist.

Indian and American electrical engineer and computer scientist.

Nasir Ahmed in 2012

The DCT is the most widely used data compression transformation, the basis for most digital media standards (image, video and audio) and commonly used in digital signal processing.