On Sun, Aug 15, 2021 at 6:05 PM Paul Buxton <paulbuxton.m...@googlemail.com> wrote:
> So construct filtergraph with > > 1. zscale with a linear transfer function > 2. color correction filter (I am calling it underwater correction, but > nothing it does is actually specific to underwater images, it is simply > a > grey world based algorithm for whitebalance). > 3. zscale with desired output transfer function (probably BT709). > > Is it normal that someone needs to know the characteristics of the filter > to such a degree that they know to apply the pre/post > linearisation/de-linearisation to use it? > > Agree filter cannot recover red where none is present, but at recreational > dive depths there is still some red present, and this does get the image > closer to what you 'see' as a diver. I think the bigger problem with this > approach is that for scenes where there is not much other color, it can > wash out the color that is there. > Compared to other algorithms, such as histogram equalisation it seems to > perform pretty well and without temporal instability which requires > smoothing to correct. > > I can throw some comparison videos up on youtube if anyone is > interested (when it finally finishes converting). > > Better provide real unprocessed underwater videos. I see no point in using different color space or floats if unprocessed video source in need for filtering is 8bit depth YUV. > I need to look into how the FATE testing stuff works and put together a > test, and make sure everything else fits with coding guidelines before > submittinga patch. But I think I would prefer to send the working floating > point version before working on a performance optimised int varient, unless > that would be against contribution guidelines.. > Any patches are welcomed. > > Paul > > > On Sun, Aug 15, 2021 at 4:09 PM Paul B Mahol <one...@gmail.com> wrote: > > > On Sun, Aug 15, 2021 at 3:43 PM Paul Buxton < > > paulbuxton.m...@googlemail.com> > > wrote: > > > > > Thanks both. > > > > > > I have implemented the algorithm in this paper > > > > > > > > > https://www.researchgate.net/publication/275213614_A_New_Color_Correction_Method_for_Underwater_Imaging > > > > > > Which basically converts to an L A B (not CIELAB) colorspace, subtracts > > the > > > average value of the frame from each pixel and converts back. > > > > > > Yes I did put the linearisation /de-linearisation into the filter. Not > > > applying it produces noticeably incorrect results. Is there instead a > way > > > to tell the filtergraph that the filter expects and outputs linear > data? > > > > > > > There is no automated thing yet, but for converting to/from linear use > > zscale filter. > > > > Also if input is 8bit depth I doubt there can be recovered much if there > is > > no red component in video. > > If input is in float that is completely different story.... > > > > > > > > > > I can investigate an integer version. > > > > > > > > > On Sun, Aug 15, 2021 at 2:31 PM Paul B Mahol <one...@gmail.com> wrote: > > > > > > > On Sun, Aug 15, 2021 at 3:27 PM Nicolas George <geo...@nsup.org> > > wrote: > > > > > > > > > Paul Buxton (12021-08-15): > > > > > > I have my filter working nicely but it is a little slow. I have > > > > > > parallelised it where possible, but it is still a bit heavy. I am > > > > > wondering > > > > > > if there are any optimised implementations/approximations of some > > > math > > > > > > functions built in that I should use instead of the standard > > library > > > > > > implementations. > > > > > > Specifically any of > > > > > > pow() > > > > > > exp() > > > > > > log() > > > > > > > > > > > > I have done a quick grep of the code but can't see any likely > > > > contenders. > > > > > > > > > > I am not aware we have those. The kind of optimization you can do > > > > > depends a lot on your use case. Please give a little details. > > > > > > > > > > If you want to speed your filter up, the best would be to make it > > work > > > > > with integers. It would also allow to make reliable unit tests. > > > > > > > > > > > > > > > > > If you convert to/from linear light inside filter, that is wrong > thing > > to > > > > do. > > > > > > > > > > > > > > > > > > Regards, > > > > > > > > > > -- > > > > > Nicolas George > > > > > _______________________________________________ > > > > > ffmpeg-devel mailing list > > > > > ffmpeg-devel@ffmpeg.org > > > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > > > > > > > > > To unsubscribe, visit link above, or email > > > > > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > > > > > > > > > _______________________________________________ > > > > ffmpeg-devel mailing list > > > > ffmpeg-devel@ffmpeg.org > > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > > > > > > > To unsubscribe, visit link above, or email > > > > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > > > > > > > _______________________________________________ > > > ffmpeg-devel mailing list > > > ffmpeg-devel@ffmpeg.org > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > > > > > To unsubscribe, visit link above, or email > > > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > > > > > _______________________________________________ > > ffmpeg-devel mailing list > > ffmpeg-devel@ffmpeg.org > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > > > To unsubscribe, visit link above, or email > > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
