Editing Compression artifact (section)

=== Image artifact reduction ===
{{Main article|Deblocking filter}}

Various approaches have been proposed to reduce image compression effects, but to use standardized compression/decompression techniques and retain the benefits of compression (for instance, lower transmission and storage costs), many of these methods focus on "post-processing"—that is, processing images when received or viewed. No post-processing technique has been shown to improve image quality in all cases; consequently, none has garnered widespread acceptance, though some have been implemented and are in use in proprietary systems. Many photo editing programs, for instance, have proprietary JPEG artifact reduction algorithms built-in. Consumer equipment often calls this post-processing "MPEG Noise Reduction".<ref>{{cite web|url=https://www.pcmag.com/encyclopedia_term/0%2C2542%2Ct%3Dblocking+artifacts%26i%3D56319%2C00.asp|title=PC Magazine, Definition of blocking artifacts|access-date=23 September 2020|archive-date=7 October 2012|archive-url=https://web.archive.org/web/20121007015121/http://www.pcmag.com/encyclopedia_term/0%2C2542%2Ct%3Dblocking+artifacts%26i%3D56319%2C00.asp|url-status=dead}}</ref>

Boundary artifact in JPEG can be turned into more pleasing "grains" not unlike those in high ISO photographic films. Instead of just multiplying the quantized coefficients with the quantisation step {{mvar|Q}} pertaining to the 2D-frequency, intelligent noise in the form of a random number in the interval {{math|1=[-''Q''/2; ''Q''/2]}} can be added to the dequantized coefficient. This method can be added as an integral part to JPEG decompressors working on the trillions of existing and future JPEG images. As such it is not a "post-processing" technique.<ref>{{cite journal |last1=Hudson |first1=Graham |last2=Léger |first2=Alain |last3=Niss |first3=Birger |last4=Sebestyén |first4=István |last5=Vaaben |first5=Jørgen |title=JPEG.1 standard 25 years: past, present and future reasons for success |journal=Journal of Electronic Imaging |date=31 August 2018 |volume=27|issue=4 |page=1 |doi=10.1117/1.JEI.27.4.040901 |s2cid=52164892 |doi-access=free }}</ref>

The ringing issue can be reduced at encode time by overshooting the DCT values, clamping the rings away.<ref>{{cite book |last1=Richter |first1=Thomas |title=2016 IEEE International Conference on Image Processing (ICIP) |chapter=JPEG on STEROIDS: Common optimization techniques for JPEG image compression |date=September 2016 |pages=61–65 |doi=10.1109/ICIP.2016.7532319 |isbn=978-1-4673-9961-6 |s2cid=14922251}}</ref>

Posterization generally only happens at low quality, when the DC values are given too little importance. Tuning the quantization table helps.<ref>{{cite web |title=kornelski/jpeg-compressor |website=[[GitHub]] |url=https://github.com/kornelski/jpeg-compressor#low-dc-quantization |date=16 November 2020}}</ref>