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ScalerCrops handling #1087

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ScalerCrops handling #1087

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naushir
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@naushir naushir commented Aug 8, 2024

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Note that this change and new functionality is only applicable on Pi 5.

The stream configuration dictionary now has a "preserve_ar" key that
when set to True, will preserve the aspect ratio of the output by
cropping the sensor image appropriately. If set to False, the full
field of view of the sensor image is used to scale to the output
resolution. This happens separately for the main and lores streams.

The default behaviour of this flag is as follows:

- For the main stream, it is set to True. This preserves existing
  behaviour.

- For the lowres stream, it is set to False, which then makes the lowres
  stream crop follows the crop of the main stream. Again, this
  preservies existing behaviour, also matching VC4.

Signed-off-by: Naushir Patuck <[email protected]>
Add this control to the ignore list.

Signed-off-by: Naushir Patuck <[email protected]>
@@ -1116,6 +1116,15 @@ def configure_(self, camera_config="preview") -> None:
self.controls = Controls(self, controls=self.camera_config['controls'])
self.configure_count += 1

if "ScalerCrops" in self.camera_controls:
par_crop = self.camera_controls["ScalerCrops"]
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Ah, I'm guessing par_crop means preserve_ar_crop? Actually, for my curiosity, how does this work? Presumably libcamera is calculating the AR-preserving crop for each of the cameras - except I thought asking for camera controls was supposed to give us min/max/default triple. So I think I'm a bit confused!

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Presumably libcamera is calculating the AR-preserving crop for each of the cameras - except I thought asking for camera controls was supposed to give us min/max/default triple. So I think I'm a bit confused!

This is a bit of a hack where the controlinfo for rpi::ScalerCrops actually gives us the default (i.e. preserved ar) crop for output 0 and output 1 in the min/max fields. Unfortunately there is no other mechanism that can be used to get this out for span controls.

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I see, yes, that's a bit sneaky! Maybe worth a comment as it was a bit head-scratchy?


for m, l in [(False, False), (False, True), (True, False), (True, True)]:
cfg = picam2.create_video_configuration(main={"size": (1920, 1080), "format": 'XRGB8888', "preserve_ar": m},
lores={"size": (640, 640), "format": 'XRGB8888', "preserve_ar": l},
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Just wondering what this does on a Pi 4 where you can't have RGB on the lores?

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Good question - I assumed the validate() would change this to YUV and everything would be good. But I've not explicitly tried it...

Actually, there's no reason lores needs to be RGB, perhaps I should just change it to YUV.

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