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

[Kieran Bingham]

Quoting Dan Scally (2024-11-06 09:39:09)
> Hi Jacopo - thanks for the review
> 
> On 04/11/2024 11:07, Jacopo Mondi wrote:
> > 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
> That was my thinking basically.

I agree here. I'm fine moving these to a common location to get started.

If things grow - or become more specific then they could be separated to
a defined structure, but that could also be done on top ... I have one
example below for that...


> >
> >> @@ -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

s/valye/value/

> >> + * \return The estimated luminance value
> > \return statements usually go after the longer function documentation
> 
> 
> Ack
> 
> >
> >
> >> + *
> >> + * 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.
> You're right, that's wrong. Thanks.
> >
> >> +{
> >> +    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

Perhaps those are both helpers for 'colorspace' so maybe this is a
colorspace.cpp ... but lets see...


> >
> >> +
> >> +/**
> >> + * \brief Convert double to Q(m.n) format
> > Note these two helpers seems to be un-used.
> Ah yes, they're used in the C55 series which will be based on top of this...I can introduce them 
> there if that's better?
> > What Q formats are we referring to ? Wikipedia lists two (TI version
> > and ARM version).
> > https://en.wikipedia.org/wiki/Q_(number_format)
> 
> 
> So far I'm only using numbers specified in documentation as being unsigned, and so it's the TI 
> version, but the "UQ" format rather than just "Q"...possibly renaming the function 
> "toUnsignedQFormat()" would be clearer?
> 
> >
> >> + * \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

Q(a.b) formats come up a lot. I'd always thought we need a FixedPoint
(templated?) class to help with this so we can consider it as a real
type.

If so - it would be it's own class, and warrant a set of unit tests...

So if you did want to split this helpers.cpp,h up - I'd move the color
space functionality to colorspace.cpp and Q helpers to fixedpoint.cpp
...

Ultimately it depends how far you want to take the cleanup...



> >
> >> +
> >> +} /* 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
> >>