[libcamera-devel,v3,10/12] ipa: ipu3: awb: Introduce Black Level Correction

14064 diff mbox series

The pixels output by the camera normally include a black level, because
sensors do not always report a signal level of '0' for black. Pixels at
or below this level should be considered black and to achieve that, we
need to substract an offset to all the pixels. This can be taken into
account by reading the lowest value of a special region on sensors which
is not exposed to light. This provides a substracting factor to be
able to adjust the expected black levels in the resulting images.

For a camera outputting 10-bit pixel values (in the range 0 to 1023) a
typical black level might be 64. It is a fixed value, obtained by
capturing a raw frame with minimum exposure and gain fixed to 1.0 while
covering the sensor (the darker the better). We consider it good enough
as a very first approximation, until we measure it during a tuning
process and include it in a configuration file

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 src/ipa/ipu3/algorithms/blc.cpp     | 66 +++++++++++++++++++++++++++++
 src/ipa/ipu3/algorithms/blc.h       | 28 ++++++++++++
 src/ipa/ipu3/algorithms/meson.build |  1 +
 src/ipa/ipu3/ipu3.cpp               |  2 +
 4 files changed, 97 insertions(+)
 create mode 100644 src/ipa/ipu3/algorithms/blc.cpp
 create mode 100644 src/ipa/ipu3/algorithms/blc.h

Hi Jean-Michel,

Thank you for the patch.

On Wed, Oct 06, 2021 at 04:00:40PM +0200, Jean-Michel Hautbois wrote:
> The pixels output by the camera normally include a black level, because
> sensors do not always report a signal level of '0' for black. Pixels at
> or below this level should be considered black and to achieve that, we
> need to substract an offset to all the pixels. This can be taken into
> account by reading the lowest value of a special region on sensors which
> is not exposed to light. This provides a substracting factor to be
> able to adjust the expected black levels in the resulting images.
> 
> For a camera outputting 10-bit pixel values (in the range 0 to 1023) a
> typical black level might be 64. It is a fixed value, obtained by
> capturing a raw frame with minimum exposure and gain fixed to 1.0 while
> covering the sensor (the darker the better). We consider it good enough
> as a very first approximation, until we measure it during a tuning
> process and include it in a configuration file
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/blc.cpp     | 66 +++++++++++++++++++++++++++++
>  src/ipa/ipu3/algorithms/blc.h       | 28 ++++++++++++
>  src/ipa/ipu3/algorithms/meson.build |  1 +
>  src/ipa/ipu3/ipu3.cpp               |  2 +
>  4 files changed, 97 insertions(+)
>  create mode 100644 src/ipa/ipu3/algorithms/blc.cpp
>  create mode 100644 src/ipa/ipu3/algorithms/blc.h
> 
> diff --git a/src/ipa/ipu3/algorithms/blc.cpp b/src/ipa/ipu3/algorithms/blc.cpp
> new file mode 100644
> index 00000000..df56e292
> --- /dev/null
> +++ b/src/ipa/ipu3/algorithms/blc.cpp
> @@ -0,0 +1,66 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google inc.
> + *
> + * blc.cpp - IPU3 Black Level Correction control
> + */
> +
> +#include "blc.h"
> +
> +#include <string.h>
> +
> +/**
> + * \file blc.h

 * \brief IPU3 Black Level Correction control

> + */
> +
> +namespace libcamera {
> +
> +namespace ipa::ipu3::algorithms {
> +
> +/**
> + * \class BlackLevelCorrection
> + * \brief A class to handle optical black correction

s/optical black correction/black level correction/

> + *
> + * The pixels output by the camera normally include a black level, because
> + * sensors do not always report a signal level of '0' for black. Pixels at or
> + * below this level should be considered black. To achieve that, the ImgU BLC
> + * algorithm subtracts a configurable offset from all pixels.
> + *
> + * The black level can be measured at runtime from an optical dark region of the
> + * camera sensor, or measured during the camera tuning process. The first option
> + * isn't currently supported.
> + */
> +
> +BlackLevelCorrection::BlackLevelCorrection()
> +{
> +}
> +
> +/**
> + * \brief Fill in the parameter structure, and enable optical black correction

s/optical black correction/black level correction/

> + * \param context The shared IPA context
> + * \param params The IPU3 parameters
> + *
> + * Populate the IPU3 parameter structure with the correction values for each
> + * channel and enable the corresponding ImgU block processing.
> + */
> +void BlackLevelCorrection::prepare([[maybe_unused]] IPAContext &context,
> +			      ipu3_uapi_params *params)
> +{
> +	/*
> +	 * The Optical Black Level correction values
> +	 * \todo The correction values should come from sensor specific
> +	 * tuning processes. This is a first rough approximation

s/$/./

> +	 */
> +	params->obgrid_param.gr = 64;
> +	params->obgrid_param.r  = 64;
> +	params->obgrid_param.b  = 64;
> +	params->obgrid_param.gb = 64;
> +
> +	/* Enable the custom optical black correction processing */
> +	params->use.obgrid = 1;
> +	params->use.obgrid_param = 1;
> +}
> +
> +} /* namespace ipa::ipu3::algorithms */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/ipu3/algorithms/blc.h b/src/ipa/ipu3/algorithms/blc.h
> new file mode 100644
> index 00000000..4b7cb483
> --- /dev/null
> +++ b/src/ipa/ipu3/algorithms/blc.h
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google inc.
> + *
> + * black_correction.h - IPU3 Black Level Correction control
> + */
> +#ifndef __LIBCAMERA_IPU3_ALGORITHMS_BLC_H__
> +#define __LIBCAMERA_IPU3_ALGORITHMS_BLC_H__
> +
> +#include "algorithm.h"
> +
> +namespace libcamera {
> +
> +namespace ipa::ipu3::algorithms {
> +
> +class BlackLevelCorrection : public Algorithm
> +{
> +public:
> +	BlackLevelCorrection();
> +
> +	void prepare(IPAContext &context, ipu3_uapi_params *params) override;
> +};
> +
> +} /* namespace ipa::ipu3::algorithms */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_IPU3_ALGORITHMS_BLC_H__ */
> diff --git a/src/ipa/ipu3/algorithms/meson.build b/src/ipa/ipu3/algorithms/meson.build
> index deae225b..3ec42f72 100644
> --- a/src/ipa/ipu3/algorithms/meson.build
> +++ b/src/ipa/ipu3/algorithms/meson.build
> @@ -4,5 +4,6 @@ ipu3_ipa_algorithms = files([
>      'agc.cpp',
>      'algorithm.cpp',
>      'awb.cpp',
> +    'blc.cpp',
>      'tone_mapping.cpp',
>  ])
> diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
> index 06f53fbe..6d9bbf39 100644
> --- a/src/ipa/ipu3/ipu3.cpp
> +++ b/src/ipa/ipu3/ipu3.cpp
> @@ -33,6 +33,7 @@
>  #include "algorithms/agc.h"
>  #include "algorithms/algorithm.h"
>  #include "algorithms/awb.h"
> +#include "algorithms/blc.h"
>  #include "algorithms/tone_mapping.h"
>  #include "libipa/camera_sensor_helper.h"
>  
> @@ -282,6 +283,7 @@ int IPAIPU3::init(const IPASettings &settings,
>  	/* Construct our Algorithms */
>  	algorithms_.push_back(std::make_unique<algorithms::Agc>());
>  	algorithms_.push_back(std::make_unique<algorithms::Awb>());
> +	algorithms_.push_back(std::make_unique<algorithms::BlackLevelCorrection>());
>  	algorithms_.push_back(std::make_unique<algorithms::ToneMapping>());
>  
>  	return 0;