Skip to main content

Lossy compression

What is lossy compression?

Lossy compression is a data encoding method that compresses a file into a smaller size by discarding some of its data. The compression process involves eliminating less important data, thereby reducing the size of the resulting file. This type of compression is commonly used in video, audio, and image files where a certain amount of data loss will not significantly degrade the content’s perceived quality.

It's important to note that once data has been compressed using lossy compression, the lost data cannot be recovered. This is a key difference between lossy and lossless compression, the latter of which allows for the original data to be perfectly reconstructed from the compressed data.

The mechanics of lossy compression

Perceptual coding

One of the main techniques used in lossy compression is perceptual coding. This method accounts for what we can see and hear by reducing unnecessary data within media files in ways that we won’t notice.

For instance, in audio files, perceptual coding can remove sounds that are masked, or covered by other louder sounds. When listening to that file, a person wouldn’t notice that the quieter sound has been removed. Similarly, in image files, lossy compression removes visual information in a way that can’t be seen by the human eye.

Quantization

Quantization is another technique used in lossy compression. It involves reducing the precision of certain parts of data to save on storage space. For example, an image file might cut down on the number of colors used in areas that look more uniform in hue, which saves data.

Quantization can lead to lower image and sound quality if it’s used too much in the encoding process. However, if used judiciously, quantization can significantly reduce the unnecessary data in a file without impacting media quality too much. quality.

Applications of lossy compression

Lossy compression is especially important when it comes to formatting and sending digital media. Some of the most common applications include:

  • Audio: Formats like MP3 and AAC use lossy compression to reduce the size of audio files. More songs can be stored on a device or streamed over the internet in MP3 format, for example.
  • Video: Formats like MPEG-2 and H.264 use lossy compression to reduce the size of video files. This way, relatively high-definition videos to be streamed over the internet without buffering problems.
  • Images: Formats like JPEG use lossy compression to reduce the size of image files. This allows for more images to be stored on a device or displayed on a webpage.

Again, it's important to be aware of the trade-off in quality when using lossy compression. In some cases, the loss of data can result in your media deceasing noticeably in quality, especially when a file is compressed multiple times.

Lossy compression: Pros and cons

Like any technology, lossy compression has its pros and cons. On the positive side, the smaller file sizes after compression make it possible to store more data on a device or transmit more data over a network. This can be particularly beneficial in situations where storage space or bandwidth is limited.

However, lossy compression always results in a loss of data, no matter how small a quantity it may be. While this loss may not be noticeable in many cases, it can become apparent when the file is compressed multiple times or when the compression ratio is high.

Furthermore, because the lost data cannot be recovered, lossy compression is not suitable for certain types of data. For example, it would not be appropriate to use lossy compression for a text file, as any loss of data could alter the content of the text itself.