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.
A program in paper tape
Solidyne 922: The world's first commercial audio bit compression sound card for PC, 1990
Processing stages of a typical video encoder

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.

- Lossy compression

Any particular compression is either lossy or lossless.

- 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.

29 related topics

Alpha

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.

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.

Uncompressed digital media as well as lossless compression had impractically high memory and bandwidth requirements, which was significantly reduced by the highly efficient DCT lossy compression technique, capable of achieving data compression ratios from 8:1 to 14:1 for near-studio-quality, up to 100:1 for acceptable-quality content.

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

JPEG

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

JPEG is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography.

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.

Image compression may be lossy or lossless.

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.

By contrast, lossy compression permits reconstruction only of an approximation of the original data, though usually with greatly improved compression rates (and therefore reduced media sizes).

MDCT window functions: blue: Cosine, red: Sine-Cosine, green: modified Kaiser-Bessel

Modified discrete cosine transform

Transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where subsequent blocks are overlapped so that the last half of one block coincides with the first half of the next block.

Transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where subsequent blocks are overlapped so that the last half of one block coincides with the first half of the next block.

MDCT window functions: blue: Cosine, red: Sine-Cosine, green: modified Kaiser-Bessel

As a result of these advantages, the MDCT is the most widely used lossy compression technique in audio data compression.

Comparison of JPEG 2000 with the original JPEG format.

JPEG 2000

Image compression standard and coding system.

Image compression standard and coding system.

Comparison of JPEG 2000 with the original JPEG format.
Top-to-bottom demonstration of the artifacts of JPEG 2000 compression. The numbers indicate the compression ratio used.
CDF 5/3 wavelet used for lossless compression.
An example of the wavelet transform that is used in JPEG 2000. This is a 2nd-level CDF 9/7 wavelet transform.
This image shows the (accentuated) difference between an image saved as JPEG 2000 (quality 50%) and the original.
Comparison of JPEG, JPEG 2000, JPEG XR, and HEIF at similar file sizes.

The standard could be adapted for motion imaging video compression with the Motion JPEG 2000 extension.

The codestream obtained after compression of an image with JPEG 2000 is scalable in nature, meaning that it can be decoded in a number of ways; for instance, by truncating the codestream at any point, one may obtain a representation of the image at a lower resolution, or signal-to-noise ratio – see scalable compression.

Original image, with good text edges and color grade

Compression artifact

Original image, with good text edges and color grade
Loss of edge clarity and tone "fuzziness" in heavy JPEG compression
Illustration of the effect of JPEG compression on a slightly noisy image with a mixture of text and whitespace. Text is a screen capture from a Wikipedia conversation with noise added (intensity 10 in Paint.NET). One frame of the animation was saved as a JPEG (quality 90) and reloaded. Both frames were then zoomed by a factor of 4 (nearest neighbor interpolation).
Block coding artifacts in a JPEG image. Flat blocks are caused by coarse quantization. Discontinuities at transform block boundaries are visible.
Example of image with artifacts due to a transmission error

A compression artifact (or artefact) is a noticeable distortion of media (including images, audio, and video) caused by the application of lossy compression.

Lossy data compression involves discarding some of the media's data so that it becomes small enough to be stored within the desired disk space or transmitted (streamed) within the available bandwidth (known as the data rate or bit rate).

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.

If lossy data compression is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifacts.