Unexpectedly expensive conversion from BGRA to BGR

[Tyler Compton]

Interesting, thank you Nicolas. Unfortunately, the majority of machine
learning models I'm using require BGR or RGB as their input format, so
there isn't a lot I can do about it right now. I guess I'll have to look
for optimizations elsewhere.

On Sat, Oct 17, 2020 at 7:38 AM Nicolas Dufresne <nicolas at ndufresne.ca>
wrote:

> Le vendredi 16 octobre 2020 à 16:10 -0700, Tyler Compton a écrit :
> > Hi everyone,
> >
> > I have a pipeline that, at some point, needs to convert video frames
> from BGRA to BGR. I was surprised to see about a ~17% increase in CPU usage
> just from doing this conversion. I wouldn't expect it to be that expensive,
> considering it's just a matter of stripping off some data for each pixel.
> >
> > In my application, I have BGRA frames, but never any actual alpha
> information. Is there perhaps an optimization opportunity because of that?
> >
> > On average I see about 17% CPU usage when running this pipeline:
> >
> > videotestsrc is-live=true !
> "video/x-raw,format=BGRA,width=1920,height=1080,framerate=30/1" ! fakesink
> >
> > However, I see around 38% CPU usage just by adding a videoconvert to go
> from BGRA to BGR:
> >
> > videotestsrc is-live=true !
> "video/x-raw,format=BGRA,width=1920,height=1080,framerate=30/1" !
> videoconvert ! "video/x-raw,format=BGR" ! fakesink
>
> This conversion will move 32bit aligned pixels to 24bits (unaligned)
> pixels. Unaligned writes are 3 time slower. Unless you need the
> bandwidth gain (even though yuv formats may give a better compression),
> I would not recommending using 24bit packed formats in recent
> applications. At least not when doing CPU access.
>
> >
> > I'm running GStreamer 1.18.0 on Ubuntu 20.04.
> >
> > Thanks,
> > Tyler
> >
> >
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