Generation loss
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Generation loss is the loss of quality between subsequent copies or transcodes of data. Anything that reduces the quality of the representation when copying, and would cause further reduction in quality on making a copy of the copy, can be considered a form of generation loss. File size increases are a common result of generation loss, as the introduction of artifacts may actually increase the entropy of the data through each generation.
Analog generation loss
In
Generation loss was a major consideration in complex analog audio and video editing, where multi-layered edits were often created by making intermediate mixes which were then "bounced down" back onto tape. Careful planning was required to minimize generation loss, and the resulting noise and poor frequency response.
One way of minimizing the number of generations needed was to use an audio mixing or video editing suite capable of mixing a large number of channels at once; in the extreme case, for example with a 48-track recording studio, an entire complex mixdown could be done in a single generation, although this was prohibitively expensive for all but the best-funded projects.
The introduction of professional
According to ATIS, "Generation loss is limited to analog recording because digital recording and reproduction may be performed in a manner that is essentially free from generation loss."[1]
Digital generation loss
Used correctly, digital technology can eliminate generation loss. This implies the exclusive use of lossless compression codecs or uncompressed data from recording or creation until the final lossy encode for distribution through internet streaming or optical discs. Copying a digital file gives an exact copy if the equipment is operating properly which eliminates generation loss caused by copying, while reencoding digital files with lossy compression codecs can cause generation loss. This trait of digital technology has given rise to awareness of the risk of unauthorized copying. Before digital technology was widespread, a record label, for example, could be confident knowing that unauthorized copies of their music tracks were never as good as the originals.
Generation loss can still occur when using lossy video or audio compression codecs as these introduce artifacts into the source material with each encode or reencode. Lossy compression codecs such as
Processing a
Techniques that cause generation loss in digital systems
In
Some
Thus careful planning of an audio or video signal chain from beginning to end and rearranging to minimize multiple conversions is important to avoid generation loss when using lossy compression codecs. Often, arbitrary choices of numbers of pixels and sampling rates for source, destination, and intermediates can seriously degrade digital signals in spite of the potential of digital technology for eliminating generation loss completely.
Similarly, when using lossy compression, it will ideally only be done once, at the end of the workflow involving the file, after all required changes have been made.
Transcoding
Converting between lossy formats – be it decoding and re-encoding to the same format, between different formats, or between different bitrates or parameters of the same format – causes generation loss.
Repeated applications of lossy compression and decompression can cause generation loss, particularly if the parameters used are not consistent across generations.
Ideally an algorithm will be both
Some lossy compression algorithms are much worse than others in this regard, being neither idempotent nor scalable, and introducing further degradation if parameters are changed.
For example, with
Editing
Digital
Resampling causes aliasing, both blurring low-frequency components and adding high-frequency noise, causing jaggies, while rounding off computations to fit in finite precision introduces quantization, causing banding; if fixed by dither, this instead becomes noise. In both cases, these at best degrade the signal's S/N ratio, and may cause artifacts. Quantization can be reduced by using high precision while editing (notably floating point numbers), only reducing back to fixed precision at the end.
Often, particular implementations fall short of theoretical ideals.
Examples
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Successive generations of photocopies result in image distortion and degradation.[3] It has been documented that successive repostings on Instagram results in noticeable changes.[4] Likewise, repeated postings on YouTube degraded the work.[5][6] Similar effects have been documented in copying of VHS tapes.[5] This is because both services use lossy codecs on all data that is uploaded to them, even if the data being uploaded is a duplicate of data already hosted on the service, while VHS is an analog medium, where effects such as noise from interference can have a much more noticeable impact on recordings.
See also
- Signal-to-noise ratio
- Editing digital images
- Lossless data compression
- Data degradation
- Data loss
- Software rot
- I Am Sitting in a Room
- The Disintegration Loops
- Ship of Theseus
Notes
- ^ a b "generation loss". ATIS Telecom Glossary. Alliance for Telecommunications Industry Solutions. September 28, 2016. Archived from the original on 2017-01-23. Retrieved September 28, 2016.
- ^ "H.264 is magic: A technical walkthrough of a remarkable technology". 2 November 2016.
- ^ "Generation loss". Webopedia. March 2007. Retrieved September 28, 2016.
- Zhang, Michael (February 11, 2015). "Experiment Shows What Happens When You Repost a Photo to Instagram 90 Times". Petapixel. Retrieved September 28, 2016.
- ^ a b Simpson, Isaac (December 4, 2013). "Copying a YouTube video 1,000 times is a descent into hell". The Daily Dot. Retrieved September 28, 2016 – via YouTube.
- ^ Zhang, Michael (June 4, 2010). "I Am Sitting in a Room, YouTube Style". Petapixel. Retrieved September 28, 2016.
External links
- Sneyers, Jon (April 10, 2016). "Generation Loss at High Quality Settings" (Video). Archived from the original on 2021-12-13. Retrieved September 29, 2016 – via YouTube.