A perceptually lossless compression is always free of [[compression artifacts]], but the inverse is not true: it is possible for a compressor to produce imagea or soundsignal that feelsappears natural but with altered contents. Such a confusion is widely present in the field of [[radiology]] (specifically for the study of [[diagnostically acceptable irreversible compression]]), where ''visually lossless'' is taken to mean anywhere from artifact-free<ref>{{cite journal |author=European Society of Radiology |title=Usability of irreversible image compression in radiological imaging. A position paper by the European Society of Radiology (ESR) |journal=Insights into Imaging |date=April 2011 |volume=2 |issue=2 |pages=103–115 |doi=10.1007/s13244-011-0071-x |doi-access=free |pmid=22347940 |pmc=3259360}}</ref> to being indistinguishable on a side-to-side view,<ref>{{cite journal |last1=Kim |first1=Kil Joong |last2=Kim |first2=Bohyoung |last3=Lee |first3=Kyoung Ho |last4=Mantiuk |first4=Rafal |last5=Richter |first5=Thomas |last6=Kang |first6=Heung Sik |title=Use of Image Features in Predicting Visually Lossless Thresholds of JPEG2000 Compressed Body CT Images: Initial Trial |journal=Radiology |date=September 2013 |volume=268 |issue=3 |pages=710–718 |doi=10.1148/radiol.13122015|doi-access=free }}</ref> neither being as stringent as the ''flicker'' test.
