[PATCH 1/6] ipa: libipa: Add miscellaneous helpers

Mon Nov 4 12:07:36 CET 2024

Hi Dan

On Thu, Oct 31, 2024 at 04:07:36PM +0000, Daniel Scally wrote:
> We start to have functions that are effectively identical crop up
> across the IPA modules. Add a file allowing those to be centralised
> within libipa so that a single implementation can be used in all of
> the IPAs.
>
> Signed-off-by: Daniel Scally <dan.scally at ideasonboard.com>
> ---
>  src/ipa/libipa/helpers.cpp | 103 +++++++++++++++++++++++++++++++++++++
>  src/ipa/libipa/helpers.h   |  23 +++++++++
>  src/ipa/libipa/meson.build |   2 +
>  3 files changed, 128 insertions(+)
>  create mode 100644 src/ipa/libipa/helpers.cpp
>  create mode 100644 src/ipa/libipa/helpers.h
>
> diff --git a/src/ipa/libipa/helpers.cpp b/src/ipa/libipa/helpers.cpp
> new file mode 100644
> index 00000000..cc0cd586
> --- /dev/null
> +++ b/src/ipa/libipa/helpers.cpp

Not a huge fan of a collection of C functions, but I guess
alternatives could be considered over-design

> @@ -0,0 +1,103 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2024, Ideas on Board Oy
> + *
> + * libipa miscellaneous helpers
> + */
> +
> +#include "helpers.h"
> +
> +#include <algorithm>
> +#include <cmath>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +/**
> + * \file helpers.h
> + * \brief Functions to reduce code duplication between IPA modules
> + */
> +
> +/**
> + * \brief Estimate luminance from RGB values following ITU-R BT.601
> + * \param[in] r The red value
> + * \param[in] g The green value
> + * \param[in] b The blue valye
> + * \return The estimated luminance value

\return statements usually go after the longer function documentation

> + *
> + * This function estimates a luminance value from a triplet of Red, Green and
> + * Blue values, following the formula defined by ITU-R Recommendation BT.601-7
> + * which can be found at https://www.itu.int/rec/R-REC-BT.601
> + */
> +unsigned int rec601LuminanceFromRGB(unsigned int r, unsigned int g, unsigned int b)

In example, in the RPi IPA, the return value is assigned to a double,
and the calculation suggests it might be worth not casing the result to
unsigned int.

> +{
> +	return (r * .299) + (g * .587) + (b * .114);
> +}
> +
> +/**
> + * \brief Estimate correlated colour temperature from RGB color space input
> + * \param[in] red The input red value
> + * \param[in] green The input green value
> + * \param[in] blue The input blue value
> + * \return The estimated color temperature

same here

> + *
> + * This function estimates the correlated color temperature RGB color space
> + * input. In physics and color science, the Planckian locus or black body locus
> + * is the path or locus that the color of an incandescent black body would take
> + * in a particular chromaticity space as the blackbody temperature changes.
> + *
> + * If a narrow range of color temperatures is considered (those encapsulating
> + * daylight being the most practical case) one can approximate the Planckian
> + * locus in order to calculate the CCT in terms of chromaticity coordinates.
> + *
> + * More detailed information can be found in:
> + * https://en.wikipedia.org/wiki/Color_temperature#Approximation
> + */
> +uint32_t estimateCCT(double red, double green, double blue)
> +{
> +	/* Convert the RGB values to CIE tristimulus values (XYZ) */
> +	double X = (-0.14282) * (red) + (1.54924) * (green) + (-0.95641) * (blue);
> +	double Y = (-0.32466) * (red) + (1.57837) * (green) + (-0.73191) * (blue);
> +	double Z = (-0.68202) * (red) + (0.77073) * (green) + (0.56332) * (blue);
> +
> +	/* Calculate the normalized chromaticity values */
> +	double x = X / (X + Y + Z);
> +	double y = Y / (X + Y + Z);
> +
> +	/* Calculate CCT */
> +	double n = (x - 0.3320) / (0.1858 - y);
> +	return 449 * n * n * n + 3525 * n * n + 6823.3 * n + 5520.33;
> +}

This seems to come straight from the IPU3 IPA, so ack to the text and
implementation

> +
> +/**
> + * \brief Convert double to Q(m.n) format

Note these two helpers seems to be un-used.

What Q formats are we referring to ? Wikipedia lists two (TI version
and ARM version).
https://en.wikipedia.org/wiki/Q_(number_format)

> + * \param[in] value The value to convert
> + * \param[in] m The number of bits used to represent the integer part
> + * \param[in] n The number of bits used to represent the fraction part
> + *
> + * This function converts a double into an unsigned Q format, clamping at the
> + * largest possible value given m and n.

\return ?

> + */
> +unsigned int toQFormat(double value, unsigned int m, unsigned int n)
> +{
> +	double maxVal = (std::pow(2, m + n) - 1) / std::pow(2, n);
> +
> +	return std::clamp(value, 0.0, maxVal) * std::pow(2, n);
> +}
> +
> +/**
> + * \brief Convert Q(m.n) formatted number to double
> + * \param[in] value The value to convert
> + * \param[in] n The number of bits used to represent the fraction part
> + *
> + * This function converts an unsigned Q formatted value into a double.
> + */
> +double fromQFormat(unsigned int value, unsigned int n)
> +{
> +	return value / std::pow(2, n);
> +}

Let's discuss these once the above is clarified

> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/helpers.h b/src/ipa/libipa/helpers.h
> new file mode 100644
> index 00000000..361b63bd
> --- /dev/null
> +++ b/src/ipa/libipa/helpers.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2024, Ideas on Board Oy
> + *
> + * libipa miscellaneous helpers
> + */
> +
> +#pragma once
> +
> +#include <stdint.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +unsigned int rec601LuminanceFromRGB(unsigned int r, unsigned int g, unsigned int b);
> +uint32_t estimateCCT(double red, double green, double blue);
> +unsigned int toQFormat(double value, unsigned int m, unsigned int n);
> +double fromQFormat(unsigned int value, unsigned int n);
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index e78cbcd6..ca4f3e28 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -6,6 +6,7 @@ libipa_headers = files([
>      'camera_sensor_helper.h',
>      'exposure_mode_helper.h',
>      'fc_queue.h',
> +    'helpers.h',
>      'histogram.h',
>      'interpolator.h',
>      'lsc_polynomial.h',
> @@ -21,6 +22,7 @@ libipa_sources = files([
>      'camera_sensor_helper.cpp',
>      'exposure_mode_helper.cpp',
>      'fc_queue.cpp',
> +    'helpers.cpp',
>      'histogram.cpp',
>      'interpolator.cpp',
>      'lsc_polynomial.cpp',
> --
> 2.30.2
>