On Fri, Jan 1, 2021 at 4:08 AM Mark Filipak (ffmpeg) <markfili...@bog.us> wrote:
> On 12/31/2020 09:50 PM, list+ffmpeg-u...@jdlh.com wrote: > > On 2020-12-31 17:25, Mark Filipak (ffmpeg) wrote: > >> 1, Median? Really? (Or maybe really average?) > >> > >> For inputs = 239+15+15+15: > >> median = (239+15)/2 = 127 > >> average = (239+15+15+15)/4 = 71 > >> For inputs = 239+239+239+15: > >> median = (239+15)/2 = 127 (again) > >> average = (239+239+239+15)/4 = 183 > > > > It jumped out at me that the expressions you are computing for "median" > don't match the definition I > > am used to. It looks like you are computing the average of the largest > and smallest samples. I > > understand "median" to be a value such that half the samples are greater > than or equal to, and half > > are less than equal to, the value. > > > > For inputs = 239+15+15+15: > > median = 15 (239, 15 >= 15; 15, 15 <= 15) > > For inputs = 239+239+239+15: > > median = 239 (239, 239 >= 239; 239, 15 <= 15) > > > > So, how to you define "median"? And how does FFmpeg? > > > > —Jim DeLaHunt > > Thank you, Jim. You are correct. I reckon I was thinking of some sort of > mean value -- there are > several versions of mean. > > Median: The middle number in a given sequence of numbers, taken as the > average of the two middle > numbers when the sequence has an even number of numbers. > > Hmmm... What sort of weighting is that? > > For inputs = 239+15+15+15: > median = (15+15)/2 = 15 > average = (239+15+15+15)/4 = 71 > For inputs = 239+239+239+15: > median = (239+239)/2 = 239 > average = (239+239+239+15)/4 = 183 > > As you see, the median winds up being either 15 or 239. > So, what's the function of 'percentile'? > Input pixels are sorted first. percentile says where in sorted list to pick pixel value. > And why is "inputs=2" not allowed? > Because it is same as mix=2 filter _______________________________________________ > ffmpeg-user mailing list > ffmpeg-user@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe". _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".