[libcamera-devel] [PATCH v3 0/6] Digital zoom
David Plowman
david.plowman at raspberrypi.com
Thu Oct 15 16:30:56 CEST 2020
Hi Laurent
Thanks for all that! The discussion is getting rather long so perhaps
I can try to wrap up all the points in the thread and sum it up at the
top here with an outline of the plan as I understand it!
1. ScalerCrop control
This will be a Rectangle indicating the crop for digital zoom. The
units will be native pixel coordinates. The (x,y) offsets should, I
think, start at (0,0) because the "top-left-most" thing you can have
should probably be signalled with (0,0) - but see below.
2. ScalerCropMaximum property
This indicates the maximum image area from which we can crop, again in
native pixel coordinates. It could be a Rectangle and we could use the
(x,y) offsets perhaps to indicate the top left coordinates in the
sensor - i.e. this would (mostly) be the analogCrop then. (Or one
could leave them as zero, in which case you might as well leave this
as a Size.)
We've talked about making this a "dynamic" ControlInfo maximum, though
it's not quite the same thing. For example, it would typically have
the "wrong" aspect ratio so taking and setting the "maximum" would
give you a weird image - would a user expect that? Also, the meaning
of the (x,y) offsets as described for the control does not align as
things stand.
3. Other stuff...
* With this scheme there's no way for an application to know what the
true pixel scale for the ScalerCrop is. Maybe that kind of information
gets exposed later. (I seem to remember wanting to expose the whole
CameraSensorInfo several months ago...)
* There's no real allowance for any cropping after binning/scaling.
Maybe you have to adjust the ScalerCropMaximum to make it look like
all the cropping is happening up front? TBD, I think.
* Pipeline handlers will all have to go around rescaling the
ScalerCrop rectangles from native to actual pixel coordinates. Maybe
there's another geometry helper function there: Rectangle
Rectangle::rescaledTo(const Size &from, const Size &to)
e.g. actualCrop = nativeCrop.rescaledTo(sensorInfo.analogCrop.size(),
sensorInfo.outputSize)
Please correct me if I've got any of that wrong. Overall I can't quite
escape the nagging feeling that there should be better ways of getting
all that information about the camera mode to an application, but
whatever mechanism we use now can be improved upon later. The basic
ScalerCrop control would not be affected, I think.
Best regards
David
On Thu, 15 Oct 2020 at 03:17, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi David,
>
> On Tue, Oct 13, 2020 at 09:36:50AM +0100, David Plowman wrote:
> > On Tue, 13 Oct 2020 at 02:45, Laurent Pinchart wrote:
> > > On Mon, Oct 12, 2020 at 07:49:31PM +0100, David Plowman wrote:
> > > > Hi Laurent
> > > >
> > > > Thanks for the comments. Some interesting points.
> > >
> > > Sorry about chiming in so late and challenging some of the base
> > > assumptions though. I'll now try not to introduce any further delay.
> > >
> > > > On Sun, 11 Oct 2020 at 22:47, Laurent Pinchart wrote:
> > > >
> > > > > Hi David,
> > > > >
> > > > > Thank you for the patches. And more than sorry for reviewing the series
> > > > > so late.
> > > > >
> > > > > On Tue, Sep 29, 2020 at 05:39:54PM +0100, David Plowman wrote:
> > > > > > Hi everyone
> > > > > >
> > > > > > Despite not originally intending to, I've actually made a version 3 of
> > > > > > the digital zoom patches, just to take care of a few things that might
> > > > > > be a bit annoying otherwise.
> > > > > >
> > > > > > 1. I've improved the description of the IspCrop control as was
> > > > > > suggested.
> > > > > >
> > > > > > 2. I've improved the description of the zoom option in cam (if we
> > > > > > decide to use this patch!), also as was proposed.
> > > > > >
> > > > > > 3. There was actually a problem with the "{}" syntax to denote zero
> > > > > > Rectangles in include/libcamera/ipa/raspberrypi.h. They were failing a
> > > > > > range type test in ControlInfoMap::generateIdmap() and so the control
> > > > > > wasn't working. I've replaced "{}" by "Rectangle{}" which seems OK.
> > > > > >
> > > > > > 4. There's been a bit of churn in the RPi pipeline handler lately so
> > > > > > rebasing gave some conflicts. I've fixed those up.
> > > > > >
> > > > > > Otherwise everything else remains the same.
> > > > >
> > > > > I've gone through the different versions of this series, and the first
> > > > > thing I want to see is that it has improved very nicely over time. Nice
> > > > > job !
> > > > >
> > > > > Configuring zoom through an absolute crop rectangle is I believe the way
> > > > > to go, so the overall approach is good in my opinion. There are however
> > > > > a few points I'd like to discuss, related to the SensorOutputSize
> > > > > property and IspCrop control.
> > > > >
> > > > > Reading through the discussion, I become increasingly aware of a topic
> > > > > that was present in the background without ever being named, and that's
> > > > > the camera pipeline model. As mentioned yesterday in a few other replies
> > > > > to selected patches in this series and its previous versions, the job of
> > > > > libcamera is to expose to applications a camera model that abstract
> > > > > hardware differences. This is not an easy job, as we have to strike the
> > > > > right balance between a higher-level inflexible but simple to use model
> > > > > that can't support many of the less common use cases, and a lower-level
> > > > > powerful but complex to use model that exposes a very large range of
> > > > > hardware features. We have implicitly defined the skeleton of such a
> > > > > model through the API of the Camera and PipelineHandler classes, but
> > > > > have never made it explicit.
> > > > >
> > > > > This needs to change. I see no reason to block the digital zoom feature
> > > > > until we finish documenting the pipeline model, but I would like to
> > > > > design the feature while thinking about the bigger picture. Here are the
> > > > > assumptions I think the pipeline model should make for devices that
> > > > > support digital zoom.
> > > > >
> > > > > - The camera pipeline starts with a camera sensor, that may implement
> > > > > binning, skipping and/or cropping.
> > > > >
> > > > > - The subsequent blocks in the pipeline may perform additional cropping,
> > > > > either at the direct command of the pipeline handler (e.g. cropping at
> > > > > the input of the scaler), or automatically to support image processing
> > > > > steps (e.g. colour interpoloation often drops a few lines and columns
> > > > > on all edges of the image).
> > > > >
> > > > > - The pipeline ends with a scaler that can implement digital zoom
> > > > > through a combination of cropping followed by scaling.
> > > > >
> > > > > The exact order of the processing steps at the hardware level doesn't
> > > > > need to match the pipeline model. For instance, cropping at the input
> > > > > and output of the scaler are interchangeable (not taking into account
> > > > > sub-pixel differences). It doesn't matter if the ISP scales before
> > > > > cropping the output, the hardware scaler parameters and output crop
> > > > > rectangle can be computed from an abstract input crop rectangle and
> > > > > output size. This is crucial to consider for the definition of the
> > > > > pipeline model: we need to design it in a way that ensures all features
> > > > > can be mapped to how they are implemented in the different types of
> > > > > hardware we want to support, but we're otherwise free to not map
> > > > > controls and properties 1:1 with the hardware parameters. When multiple
> > > > > options are possible, we should be guided by API design criteria such as
> > > > > coherency, simplicity and flexibility.
> > > > >
> > > > > Coming back to digital zoom, this series exposes a new SensorOutputSize
> > > > > property and a new IspCrop control. The SensorOutpuSize property is
> > > > > introduced to support the IspCrop control, as the base rectangle in
> > > > > which the scaler can crop. There are two issues here that bother me:
> > > > >
> > > > > - The property, despite being named SensorOutputSize, potentially takes
> > > > > into account the cropping added by the CSI-2 receiver and by the ISP
> > > > > for operations that consume lines and columns on the edges of the
> > > > > image. The naming can create some confusion, which can possibly be
> > > > > addressed by a combination of documentation (you're covering that
> > > > > already) and possibly a more explicit name for the property. However,
> > > > > as the property bundles crop operations perfomed in different stages
> > > > > of the pipeline, I'm worried that it will turn out to be a bit
> > > > > ill-defined regardless of how well we document it, with slightly
> > > > > different behaviours in different implementations.
> > > > >
> > > > > - Ignoring the additional cropping performed in the CSI-2 receiver and
> > > > > ISP (if any), the property exposes the sensor binning, skipping and
> > > > > cropping. It bundles those three operations together, and thus doesn't
> > > > > convey how the cropping affects the field of view as a given output
> > > > > size can be achieved with different combinations of skipping/binning
> > > > > and cropping.
> > > > >
> > > > > For these reasons, I'm concerned that the SensorOutputCrop property is a
> > > > > ad-hoc solution to provide a reference for the IspCrop property, and
> > > > > will not fit clearly in a pipeline model that should be based on simple,
> > > > > base building blocks. I would thus like to propose an alternative
> > > > > option.
> > > > >
> > > > > Instead of expressing the IspCrop controls (which I think we should
> > > > > rename to ScalerCrop) relatively to the SensorOutputSize property, could
> > > > > we express it relatively to the existing PixelArrayActiveAreas property
> > > > > ? This would have the advantage, in my opinion, of abstracting binning
> > > > > and skipping from applications. The pipeline handlers would need to
> > > > > perform a bit more work to compute the crop rectangle actually applied
> > > > > to the scaler, in order to take sensor binning/skipping and all
> > > > > additional cropping in the pipeline into account. The upside is that the
> > > > > ScalerCrop will directly define how the field of view is affected. It
> > > > > would also simplify the API, as no intermediate property between
> > > > > PixelArrayActiveAreas and ScalerCrop would need to be defined, and the
> > > > > ScalerCrop coordinates wouldn't depend on the active camera
> > > > > configuration. I think this would be easier to clearly document as part
> > > > > of a camera pipeline model.
> > > >
> > > > Renaming IspCrop to ScalerCrop sounds fine to me. It has had so many
> > > > different names!
> > > >
> > > > I'm less sure about trying to derive the SensorOutputSize (or
> > > > ScalerInputSize or whatever else we want to call it!) from the
> > > > PixelArrayActiveAreas property. Let me try and take a step back.
> > > >
> > > > So first, I think knowing the PixelArrayActiveArea isn't enough. How would
> > > > you know if the pipeline handler was doing some extra cropping that wasn't
> > > > "strictly necessary", perhaps to reduce memory traffic, or for a faster
> > > > framerate. How would the application know not to try and zoom there? It
> > > > seems to me that this really is a decision for the pipeline handler based
> > > > on the sensor driver, it isn't available from the properties of the sensor
> > > > itself.
> > > >
> > > > Actually I'd quite like to leave the discussion there for the moment and
> > > > see if that much is controversial or not. Of course we then have to move on
> > > > but maybe let's see what we think about that first...
> > > >
> > > > Thoughts??
> > >
> > > I fully agree with you that the pipeline handler has the last word when
> > > it comes to the (combined) internal cropping. It may not have any choice
> > > (if the CFA interpolation eats two or four lines and columns on each
> > > side of the image due to the hardware implementation, there's nothing
> > > that can be done against it), or may just want to decide on policies for
> > > whatever reason it sees fit (while trying not to over-police though, to
> > > leave options to applications).
> > >
> > > My proposal doesn't deny this from the pipeline handler, but tries to
> > > express the crop rectangle in a way that maps directly to the field of
> > > view. To do so, binning/skipping would be hidden from applications by
> > > using a reference for the ScalerCrop property that has no
> > > binning/skipping applied.
> >
> > So we certainly agree on the necessity for "something", that's good,
> > and then it's a case of figuring out what "something" is. I have
> > several conflicting thoughts here (I frequently disagree with myself):
> >
> > * Actually, as a basic principle, I think applications should be able
> > to find out "the truth" if they want it. This would mean the sensor
> > crop, binning/scaling, and any subsequent cropping.
>
> I agree. I can even foresee that a low-level API to control the sensor
> parameters explicitly could be useful in some advanced cases. That
> should be an add-on though, it shouldn't cause the main API to be more
> convoluted.
>
> > * I even wonder sometimes whether there shouldn't really be a class
> > that describes how the camera mode has been derived from the sensor,
> > with all this information made explicit. But I think that leads us
> > even deeper into the woods, and I suspect we don't really want to go
> > there! (Also, I'm not sure if the V4L2 API would even let you discover
> > all of it, which might be a problem...)
>
> I think we will go there :-) I expect sensors to require more complex
> configurations in the future, as the MIPI CCS spec gets adopted. The
> kernel driver will expose 2 or 3 subdevs, and we will have a class to
> abstract that in libcamera to make it easier for pipeline handlers.
>
> > * But I also think digital zoom needs to be easy to use for
> > applications that don't care about all these details ("the truth", as
> > I called it!). Actually I feel the overwhelming majority of
> > applications will fall into this category.
>
> We're on the same page, good :-)
>
> > > The pipeline handler would restrict the requested ScalerCrop control
> > > based on the internal cropping that is always applied (combining sensor,
> > > CSI-2 receiver and ISP), and report the result through the request
> > > metadata. The application would thus know the exact crop rectangle that
> > > has been used, in unscaled (binning/skipping) sensor coordinates.
> >
> > Let me try and paraphrase a bit and you can tell me if I've got it wrong.
> >
> > You're proposing a property (details in a moment) that can be used to
> > choose zoom regions for the ScalerCrop control.
> >
> > The units for this property are the native sensor pixels, ignoring any
> > binning/scaling that might be going on.
> >
> > The property would give you a Rectangle that expresses exactly the
> > area in which you are permitted to zoom? The offset of the rectangle
> > tells you where in the sensor array this rectangle actually lies.
> >
> > The term "sensor array" there needs some clarification. I think it
> > probably means the "PixelArraySize" less any invalid or optical black
> > pixels. (Do we have a way to get hold of that easily?)
>
> I think we should use PixelArrayActiveAreas, while we may be able to
> capture dark pixels with some sensors, I think they're out of scope for
> digital zoom.
>
> My proposal initially didn't include a new property to express the area
> in which we can zoom. I was considering reporting that through the
> ScalerCrop maximum value. Every control exposed by a pipeline handler
> has a ControlInfo instance associated with it, to report the minimum,
> default and maximum values. I was thinking about reporting the area in
> which we can zoom as the maximum value of the ControlInfo for the
> ScalerCrop control. This would give applications all the information
> they need, without the need to introduce a new property.
>
> The issue with this is that ControlInfo is currently static, so we can't
> change the ScalerCrop reported maximum value when the camera is
> configured. On the other hand, properties are supposed to be static too.
> As we need to report the maximum dynamically, we will need to either
> allow ControlInfo to be dynamic, or properties to be dynamic. A change
> in behaviour is thus required, which lead me to think we should
> investigate the ControlInfo path.
>
> This being said, I don't want to delay this feature much longer, so I'm
> fine adding a new property to report the ScalerCrop maximum value (we
> could name it ScalerCropMaximum or ScalerCropBound for instance) for
> now, with the property value being updated when the camera is
> configured. We can then explore making ControlInfo dynamic, and if it
> turns out to be a good idea, drop the ScalerCropBound in the future.
>
> > The ScalerCrop requested, and reported back, gives the offset and size
> > of the zoom rectangle relative to the rectangle given by the property
> > under discussion here (I think that's the most convenient choice). So
> > if it reports back offsets of (0,0) then you know you're in the top
> > left hand corner of what you could possibly ever see in this camera
> > mode (but not necessarily of the sensor as a whole).
> >
> > I think this could work and is a fair compromise between the amount of
> > information and the ease of use. Most digital zoom applications could
> > simply request its Size, and go from there. Only a few minor
> > mis-givings:
> >
> > * Does V4L2 actually give you a way of finding out where a particular
> > "camera mode" lies in the pixel array? Do you even know if a mode is
> > binned or heavily cropped... someone who knows rather more about V4L2
> > needs to answer that one!
>
> This is exactly why we have implemented the read-only subdev API, to
> allow userspace to query detailed information about the current mode.
> The amount of information that can be extracted from the sensor driver
> depends on how the driver models the sensor. In order to expose analog
> crop, binning, skipping and digital crop separately, we would need to
> expose as least two subdevs to userspace. That's the direction I want to
> take, and libcamera will be able to handle that, but it means some
> extra work on the kernel side to implement this in sensor drivers (it's
> no rocket science though).
>
> > * Use of native sensor coords is OK, though a few sensors might
> > support non-integer scaling at which point the property would be
> > slightly "approximate". That seems fairly minor to me, though. (Some
> > ISPs might even do non-integer cropping, so the problem can exist
> > regardless.)
>
> If a sensor implements scaling in addition to cropping, binning and
> skipping, three subdevs will be required :-) That's how the smiapp
> driver is implemented today, and the new ccs driver ("[PATCH 000/100]
> CCS driver" on the linux-media mailing list) follows the same path (it
> actually replaces the smiapp driver, implementing support for both
> SMIA++ and CCS).
>
> > * It doesn't really support my assertion that you should be able to
> > know exactly what's going on, if you want to. (But if we decide this
> > doesn't matter, then that's fine too.)
>
> It doesn't by itself, but we could then add additional properties, or
> extra information in the CameraConfiguration, to report the detailed
> configuration of the sensor. What I like with this approach is that not
> only the two will not conflict (we will be able to add the properties or
> extend CameraConfiguration without touching the digital zoom API), but
> the will be no overlap between the two features either, they will each
> have one dedicated purpose.
>
> > * In one of our early discussions we suggested that having the exact
> > pixel level information might be useful, and you could do things like
> > pan one pixel at a time. We lose that by going to native sensor
> > coordinates. I think I said at the time that this ability feels more
> > useful than I believe it really is, so I wouldn't be too upset.
>
> I'm not sure to follow you here, why wouldn't we be able to pan by one
> pixel ? If the sensor is configured with binning/skipping an application
> would have to pan by 2 pixels to achieve an effective cropping of 1
> pixel, so maybe we will need to report a step, or just report
> binning/skipping factors, but with the proposed API the crop rectangle
> can be set to a pixel-perfect position. Or am I missing something ?
>
> > > While in some use cases the actual crop rectangle reported through
> > > metadata would be enough (for instance, in a GUI that starts with an
> > > unzoomed view, the application would get the maximum possible crop
> > > rectangle in the metadata of the first frame), I can imagine we would
> > > have use cases that need this information before capturing the first
> >
> > Indeed. And I also think you should be able to set digital zoom to
> > take effect *on* the very first frame itself (this spills over into
> > Naush's most recent patch set...)
>
> Yes, I think we should allow that, even if most use cases will likely
> not need it.
>
> > > frame. I initially thought we could report it through the max value of
> > > the ControlInfo instance for the ScalerCrop control, but this is
> > > supposed to be static information. As this would be (in my opinion) a
> > > neat solution, I'd like to investigate the possibility of making
> > > ControlInfo dynamic, but maybe we will need a different solution. For
> > > foresee the addition of an API that will create request templates,
> > > filling them with default control values based on a requested use case,
> > > and the maximum ScalerCrop could possibly be reported through that
> > > mechanism. I'm also fine reporting it through a temporary mechanism (for
> > > instance adding it to CameraConfiguration, or creating a dynamic
> > > property) for the time being, if you already have pressing use cases for
> > > knowing the maximum value before capturing the first frame.
> > >
> > > Thoughts ? :-)
> >
> > I'm glad we're talking about all this stuff!!
> >
> > > > > Two additional points I'd like to consider (and which are orthogonal to
> > > > > the previous one) are:
> > > > >
> > > > > - Should we automatically adjust the ScalerCrop rectangle to always
> > > > > output square pixels, or should we allow modifying the aspect ratio
> > > > > when scaling ? Most use cases call for square pixels, but I don't
> > > > > think we necessarily want to create an artificial limitation here (as
> > > > > long as we make it easy for applications to compute the scaling
> > > > > parameters that will give them square pixels)/
> > > >
> > > > Personally I see no reason to restrict what an application can request. We
> > > > need to make it easy to request the right aspect ratio (hence those
> > > > geometry helpers), but if people actually have a use-case for something
> > > > strange...
> > >
> > > Fine with me.
> > >
> > > > > - Should we allow a ScalerCrop rectangle smaller than the stream output
> > > > > size, or should we restrict scaling to down-scaling only ?
> > > >
> > > > I think up-scaling is probably the most common use-case for us (though
> > > > downscaling will happen too). Think of all those (rubbish) 30x zoom
> > > > pictures that some phones like to produce...!
> > >
> > > Rubbish is exactly the work I would have used :-) I'm tempted to try and
> > > teach users that they shouldn't do this by disabling this feature, but
> > > that would be pretentious. I suppose there's no good reason to forbid
> > > this. Should we put a limit on the upscaling factor though ?
> >
> > Always tricky. To what extent should we save people from themselves?
> > I'm pretty sure the Pi imposes some kind of a limit, but don't really
> > know. In the end, so long as it doesn't blow up, that's kind of OK...
>
> Maybe we'll introduce the concept of soft and hard limits in the future,
> with the soft limit being what the pipeline handler recommends not to
> exceed to guarantee "reasonable" quality, and the hard limit being what
> you can get out of the hardware. If someone finds a good use case for
> x100 digital zoom, I'll be curious to hear about it. We unfortunately
> don't have the same ISPs as in those movies where a 4 pixels detail in
> an image can be zoomed in full screen :-)
>
> > > > > > David Plowman (6):
> > > > > > libcamera: Add SensorOutputSize property
> > > > > > libcamera: Initialise the SensorOutputSize property
> > > > > > libcamera: Add IspCrop control
> > > > > > libcamera: Add geometry helper functions
> > > > > > libcamera: pipeline: raspberrypi: Implementation of digital zoom
> > > > > > cam: Add command line option to test IspCrop control
> > > > > >
> > > > > > include/libcamera/geometry.h | 20 +++
> > > > > > include/libcamera/ipa/raspberrypi.h | 1 +
> > > > > > src/cam/capture.cpp | 25 +++-
> > > > > > src/cam/capture.h | 2 +-
> > > > > > src/cam/main.cpp | 3 +
> > > > > > src/cam/main.h | 1 +
> > > > > > src/ipa/raspberrypi/raspberrypi.cpp | 7 +
> > > > > > src/libcamera/camera_sensor.cpp | 6 +
> > > > > > src/libcamera/control_ids.yaml | 12 ++
> > > > > > src/libcamera/geometry.cpp | 129 ++++++++++++++++++
> > > > > > .../pipeline/raspberrypi/raspberrypi.cpp | 47 +++++++
> > > > > > src/libcamera/property_ids.yaml | 19 +++
> > > > > > 12 files changed, 269 insertions(+), 3 deletions(-)
>
> --
> Regards,
>
> Laurent Pinchart
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