[libcamera-devel] qcam display scale bug

[Naushir Patuck]

Hi Hermann,

On Tue, 7 Jul 2020 at 11:09, <hermann at stamm-wilbrandt.de> wrote:
>
> Hi Naushir,
>
> I could do the experiment you asked for.
>
> But I seem accidentially having uncovered that it is a Raspberry X11
> only issue.
> I did run
> $ LIBCAMERA_LOG_LEVELS=RPiFocus:DEBUG build/src/qcam/qcam
> in an ssh session with X11 forwarding
> $ ssh -X pi at 192.168.178.44
>
> That qcam window that I saw looked better, and I took a screenshot:
> https://stamm-wilbrandt.de/en/libcamera/qcam.ssh_X.screenshot.png
>
> The top left coordinate is 10,84, bottom right is 809,684.
> So when qcam app is displayed on my RHEL 7.8, I get 800x600 as
> requested.
> Only when started on Raspberry, I only get 800x472.
> I get same 800x472 frames on X11 HDMI and X11 DPMI display -- its same
> X11.
> So it seems to be a Raspberry X11 only qcam display scale issue.
>
> Can you please start qcam like I did on Raspberry, take a screenshot and
> measure top left and bottom right coordinates of displayed frame?
> And see whether you get 800x600 or 800x472 or something else.
> "dtoverlay=vc4-fkms-v3d" is commented out in my /boot/config.txt

I seem to get 800x600 as expected.  "dtoverlay=vc4-fkms-v3d" is
enabled in my build, not sure how (if) that would make any difference.

Thanks,
Naush

>
> Thanks,
>
> Hermann.
>
> On 2020-07-07 10:28, Naushir Patuck wrote:
> > Hi Hermann,
> >
> > On Tue, 7 Jul 2020 at 08:02, <hermann at stamm-wilbrandt.de> wrote:
> >>
> >> Hi Laurent,
> >>
> >> > I assume you're using the new HQ camera, right ?
> >> >
> >> yes, but from looking into the code that should not make a difference.
> >>
> >> > I'd like to clarify this first, to make sure I understand the problem
> >> > correctly. Do you mean that qcam display a captured frame of 800x472
> >> > pixels in a 800x600 screen region, scaling it in a way that doesn't
> >> > preserve square pixels ? Do you just start the qcam application without
> >> > passing it any parameter or resizing the window, or do you perform any
> >> > specific operation ?
> >> >
> >> Yes, I am calling qcam without parameters.
> >> qcam application requests 800x600 frames (see "size"):
> >>
> >> libcamera/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> >>                  case StreamRole::Viewfinder:
> >>                          fmts =
> >> data->isp_[Isp::Output0].dev()->formats();
> >>                          pixelFormat = formats::ARGB8888;
> >>                          size = { 800, 600 };
> >>                          bufferCount = 4;
> >>                          outCount++;
> >>                          break;
> >>
> >> libcamera determines "2028x1520 pbCC" as best fit per log output.
> >> The 2028x1520 frames captured get scaled into the display frame.
> >> If the display frame would be 800x600 as requested, all would be fine.
> >> But display frame being 800x472 compresses captured frame vertically
> >> by factor 600/472=1.27.
> >
> > The 2028x1520 frame actually gets cropped in the ISP to correct for
> > the requested aspect ratio before getting resized to the 800x600
> > resolution.   So, the flow is actually as follows:
> >
> > 2028x1520 (sensor) -> 2026x1520 (aspect ratio crop) -> 800x600 (isp
> > resize).
> >
> > The reason for the crop in the middle is that the 800/600 aspect ratio
> > is exactly 4/3, but 2028/1520 is not.  This is why there will be a
> > small amount of mismatch.  Having said that, you seem to be seeing a
> > much bigger variation that does not correspond to the calculations
> > that take place.
> >
> >
> >>
> >> I verified that by picture of micrometer:
> >> https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=278268&p=1690839#p1690839
> >> The longest divisions are of length 300µm vertically, but show only
> >> 221px in display. Horizontally I measured 281px for 300µm.
> >>
> >
> > Could you try getting qcam to output 2028x1520 so that no crop/resize
> > takes place just to confirm your measurements are correct?
> >
> > Thanks,
> > Naush
> >
> >> I just see that the 800x600 is specified in raspberrypi.cpp.
> >> Can you please start qcam on some non-Raspberry system passing
> >> width=800
> >> and height=600, and then take screenshot and use image processing (I
> >> use
> >> gimp) to measure size of displayed frame?
> >>
> >>
> >> On 2020-07-07 01:30, Laurent Pinchart wrote:
> >> > Hi Hermann,
> >> >
> >> > (CC'ing Naush)
> >> >
> >> > On Sun, Jul 05, 2020 at 09:44:15PM +0200, hermann at stamm-wilbrandt.de
> >> > wrote:
> >> >> I started working with libcamera on Raspberry Pi.
> >> >
> >> > Thank you for your interest in the project :-)
> >> >
> >> >> I cannot tell whether this scale bug exists for raspberrypi only, or
> >> >> in
> >> >> general.
> >> >>
> >> >> qcam app requests a 800x600 window, but displayed window is 800x472
> >> >> only.
> >> >> This is not acceptable when using qcam as microscope app:
> >> >> https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=278268&p=1690839#p1690839
> >> >
> >> > I assume you're using the new HQ camera, right ?
> >> >
> >> >> The best mode selected by libcamera is 2028x1520 which is 4:3.
> >> >> So 800x600 (also 4:3) is needed for display.
> >> >>
> >> >> It would be helpful to know whether qcam display is also 800x472
> >> >> instead
> >> >> of 800x600 when not running on Rasberry Pi.
> >> >
> >> > I'd like to clarify this first, to make sure I understand the problem
> >> > correctly. Do you mean that qcam display a captured frame of 800x472
> >> > pixels in a 800x600 screen region, scaling it in a way that doesn't
> >> > preserve square pixels ? Do you just start the qcam application without
> >> > passing it any parameter or resizing the window, or do you perform any
> >> > specific operation ?