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

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.

Speech 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.

Speech coding is an application of data compression of digital audio signals containing speech.

Seismic wavelet

Wavelet

Wave-like oscillation with an amplitude that begins at zero, increases or decreases, and then returns to zero one or more times.

Wave-like oscillation with an amplitude that begins at zero, increases or decreases, and then returns to zero one or more times.

Seismic wavelet
D4 wavelet
STFT time-frequency atoms (left) and DWT time-scale atoms (right). The time-frequency atoms are four different basis functions used for the STFT (i.e. four separate Fourier transforms required). The time-scale atoms of the DWT achieve small temporal widths for high frequencies and good temporal widths for low frequencies with a single transform basis set.
Signal denoising by wavelet transform thresholding

Generally, an approximation to DWT is used for data compression if a signal is already sampled, and the CWT for signal analysis.

The first scan done by the SEAC in 1957

Digital image

Image composed of picture elements, also known as pixels, each with finite, discrete quantities of numeric representation for its intensity or gray level that is an output from its two-dimensional functions fed as input by its spatial coordinates denoted with x, y on the x-axis and y-axis, respectively.

Image composed of picture elements, also known as pixels, each with finite, discrete quantities of numeric representation for its intensity or gray level that is an output from its two-dimensional functions fed as input by its spatial coordinates denoted with x, y on the x-axis and y-axis, respectively.

The first scan done by the SEAC in 1957
The SEAC scanner

Rapid advances in digital imaging began with the introduction of MOS integrated circuits in the 1960s and microprocessors in the early 1970s, alongside progress in related computer memory storage, display technologies, and data compression algorithms.

An example of the 2D discrete wavelet transform that is used in JPEG2000. The original image is high-pass filtered, yielding the three large images, each describing local changes in brightness (details) in the original image. It is then low-pass filtered and downscaled, yielding an approximation image; this image is high-pass filtered to produce the three smaller detail images, and low-pass filtered to produce the final approximation image in the upper-left.

Discrete wavelet transform

Any wavelet transform for which the wavelets are discretely sampled.

Any wavelet transform for which the wavelets are discretely sampled.

An example of the 2D discrete wavelet transform that is used in JPEG2000. The original image is high-pass filtered, yielding the three large images, each describing local changes in brightness (details) in the original image. It is then low-pass filtered and downscaled, yielding an approximation image; this image is high-pass filtered to produce the three smaller detail images, and low-pass filtered to produce the final approximation image in the upper-left.
237x237px
237x237px
A 3 level filter bank
Frequency domain representation of the DWT
An example of computing the discrete Haar wavelet coefficients for a sound signal of someone saying "I Love Wavelets." The original waveform is shown in blue in the upper left, and the wavelet coefficients are shown in black in the upper right. Along the bottom are shown three zoomed-in regions of the wavelet coefficients for different ranges.

Most notably, it is used for signal coding, to represent a discrete signal in a more redundant form, often as a preconditioning for data compression.

Inter-frame prediction process. In this case, there has been an illumination change between the block at the reference frame and the block which is being encoded: this difference will be the prediction error to this block.

Inter frame

Inter-frame prediction process. In this case, there has been an illumination change between the block at the reference frame and the block which is being encoded: this difference will be the prediction error to this block.
Illustration of dependencies of the group of pictures scheme IBBPBB... Time goes from left to right.
400px

An inter frame is a frame in a video compression stream which is expressed in terms of one or more neighboring frames.

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.

OptimFROG

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.

OptimFROG is a proprietary lossless audio data compression codec developed by Florin Ghido.

An equal-loudness contour. Note peak sensitivity around 2–4 kHz, in the middle of the voice frequency band.

Psychoacoustics

Branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds.

Branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds.

An equal-loudness contour. Note peak sensitivity around 2–4 kHz, in the middle of the voice frequency band.
Audio masking graph
Perceptual audio coding uses psychoacoustics-based algorithms.
Psychoacoustic model

Data compression techniques, such as MP3, make use of this fact.

Comparison of JPEG 2000 with the original JPEG format.

Motion JPEG 2000

File format for motion sequences of JPEG 2000 images and associated audio, based on the MP4 and QuickTime format.

File format for motion sequences of JPEG 2000 images and associated audio, based on the MP4 and QuickTime format.

Comparison of JPEG 2000 with the original JPEG format.

In contrast to the original 1992 JPEG standard, which is a discrete cosine transform (DCT) based lossy compression format for static digital images, JPEG 2000 is a discrete wavelet transform (DWT) based compression standard that could be adapted for motion imaging video compression with the Motion JPEG 2000 extension.

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.

Vorbis logo

Vorbis

Free and open-source software project headed by the Xiph.Org Foundation.

Free and open-source software project headed by the Xiph.Org Foundation.

Vorbis logo

The project produces an audio coding format and software reference encoder/decoder (codec) for lossy audio compression.