Compression artifact

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Example of compression artifacts in a JPEG image

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Compression artifacts are noticeable distortions of media (including images, audio, and video) caused by the application of lossy data compression. Lossy compression algorithms are designed to reduce file size by removing some of the data, which can result in a loss of quality. Compression artifacts are particularly common in digital media formats such as JPEG for images, MP3 for audio, and MPEG for video.

Types of Compression Artifacts

Image Compression Artifacts

Image compression artifacts are often seen in formats like JPEG, where the compression process can lead to visible distortions. Common types of image compression artifacts include:

• Blocking: This occurs when the image is divided into blocks, and each block is compressed separately. The boundaries between blocks can become visible, especially at low bit rates. This is known as "macroblocking".

• Ringing: This artifact appears as a halo around sharp edges in the image. It is caused by the quantization of high-frequency components.

• Color banding: This occurs when smooth gradients are represented with a limited number of colors, resulting in visible "bands" of color.

Macroblocking effect in a JPEG image

Audio Compression Artifacts

In audio, compression artifacts can manifest as a loss of clarity, distortion, or "warbling" sounds. Common audio artifacts include:

• Pre-echo: A faint sound that precedes the main sound, often noticeable in percussive audio.

• Quantization noise: A type of noise introduced by the quantization process in lossy compression.

Video Compression Artifacts

Video compression artifacts can include both image and audio artifacts, as well as:

• Motion artifacts: These occur when the compression algorithm fails to accurately predict motion between frames, leading to "ghosting" or "blurring" effects.

• Mosquito noise: This appears as random noise around edges, especially in areas of high contrast.

Causes of Compression Artifacts

Compression artifacts are primarily caused by the reduction of data in the compression process. Lossy compression algorithms, such as those used in JPEG, MP3, and MPEG, aim to reduce file size by removing data that is deemed less important. However, this can lead to:

• Loss of detail: Fine details may be lost, leading to a "soft" appearance in images or a "muffled" sound in audio.
• Distortion: The removal of data can introduce distortions, such as blocking or ringing in images.

Mitigation Strategies

To reduce the impact of compression artifacts, several strategies can be employed:

• Use higher bit rates: Increasing the bit rate can reduce the severity of artifacts, as more data is retained.
• Use better compression algorithms: Advanced algorithms can achieve better quality at the same bit rate.
• Post-processing: Techniques such as deblocking filters can be applied to reduce visible artifacts.

Also see

• Lossy compression
• JPEG
• MP3
• MPEG
• Data compression