[PATCH v5 10/10] libcamera: software_isp: Apply CCM in debayering
Stefan Klug
stefan.klug at ideasonboard.com
Tue Feb 4 14:08:59 CET 2025
Hi Milan,
On Mon, Feb 03, 2025 at 11:26:14PM +0100, Milan Zamazal wrote:
> Milan Zamazal <mzamazal at redhat.com> writes:
>
> > Milan Zamazal <mzamazal at redhat.com> writes:
> >
> >> This patch applies color correction matrix (CCM) in debayering if the
> >> CCM is specified. Not using CCM must still be supported for performance
> >> reasons.
> >>
> >> The CCM is applied as follows:
> >>
> >> [r1 r2 r3]
> >> [r g b] * [g1 g2 g3]
> >> [b1 b2 b3]
> >
> > I think this should actually be:
> >
> > [r1 g1 b1] [r]
> > [r2 g2 b2] * [g]
> > [r3 g3 b3] [b]
This is the one that is usually used. The color is represented as
column. But mathematically both are equivalent. You wrote the transposed
notation.
out = M * c
is equivalent to
out^T = c^T * M^T
> >
> > Unless somebody corrects me, I'll change this in v6.
>
> Or maybe not. There is a bug in applying the CCM color tables in
> debayering, which confused me. If anybody knows which of the formats
> above applies to the CCMs in the tuning files, please tell me.
As noted above, the second form is used. In the tuning files they are
written in row major order [r1, g1, b1, r2, g2, b2, r3, g3, b3]. A nice
trick to check that is that every row usually sums up to one. This is
needed so that the CCM does preserves grey colors.
Best regards,
Stefan
>
> > I was unsure which is the correct version, I couldn't find it documented
> > anywhere. I can't remember why I selected the original version
> > eventually. But the second one produces much better images with the
> > matrices I copied from another pipeline for my sensor and it's also used
> > by matrices in RGB<->YUV conversion recipes so I guess that one is
> > actually right. Of course, it's just about the format of the input
> > matrices, nothing else changes.
> >
> >> The CCM matrix (the right side of the multiplication) is constant during
> >> single frame processing, while the input pixel (the left side) changes.
> >> Because each of the color channels is only 8-bit in software ISP, we can
> >> make 9 lookup tables with 256 input values for multiplications of each
> >> of the r_i, g_i, b_i values. This way we don't have to multiply each
> >> pixel, we can use table lookups and additions instead. Gamma (which is
> >> non-linear and thus cannot be a part of the 9 lookup tables values) is
> >> applied on the final values rounded to integers using another lookup
> >> table.
> >>
> >> We use int16_t to store the precomputed multiplications. This seems to
> >> be noticeably (>10%) faster than `float' for the price of slightly less
> >> accuracy and it covers the range of values that sane CCMs produce. The
> >> selection and structure of data is performance critical, for example
> >> using bytes would add significant (>10%) speedup but would be too short
> >> to cover the value range.
> >>
> >> The color lookup tables can be represented either as unions,
> >> accommodating tables for both the CCM and non-CCM cases, or as separate
> >> tables for each of the cases, leaving the tables for the other case
> >> unused. The latter is selected as a matter of preference.
> >>
> >> The tables are copied (as before), which is not elegant but also not a
> >> big problem. There are patches posted that use shared buffers for
> >> parameters passing in software ISP (see software ISP TODO #5) and they
> >> can be adjusted for the new parameter format.
> >>
> >> Color gains from white balance are supposed not to be a part of the
> >> specified CCM. They are applied on it using matrix multiplication,
> >> which is simple and in correspondence with future additions in the form
> >> of matrix multiplication, like saturation adjustment.
> >>
> >> With this patch, the reported per-frame slowdown when applying CCM is
> >> about 45% on Debix Model A and about 75% on TI AM69 SK.
> >>
> >> Using std::clamp in debayering adds some performance penalty (a few
> >> percent). The clamping is necessary to eliminate out of range values
> >> possibly produced by the CCM. If it could be avoided by adjusting the
> >> precomputed tables some way then performance could be improved a bit.
> >>
> >> Signed-off-by: Milan Zamazal <mzamazal at redhat.com>
> >> ---
> >> .../internal/software_isp/debayer_params.h | 15 ++++-
> >> src/ipa/simple/algorithms/lut.cpp | 65 ++++++++++++++-----
> >> src/ipa/simple/algorithms/lut.h | 1 +
> >> src/libcamera/software_isp/debayer.cpp | 52 ++++++++++++++-
> >> src/libcamera/software_isp/debayer_cpu.cpp | 35 ++++++++--
> >> src/libcamera/software_isp/debayer_cpu.h | 4 ++
> >> 6 files changed, 145 insertions(+), 27 deletions(-)
> >>
> >> diff --git a/include/libcamera/internal/software_isp/debayer_params.h b/include/libcamera/internal/software_isp/debayer_params.h
> >> index 7d8fdd48..9a7dbe93 100644
> >> --- a/include/libcamera/internal/software_isp/debayer_params.h
> >> +++ b/include/libcamera/internal/software_isp/debayer_params.h
> >> @@ -1,6 +1,6 @@
> >> /* SPDX-License-Identifier: LGPL-2.1-or-later */
> >> /*
> >> - * Copyright (C) 2023, 2024 Red Hat Inc.
> >> + * Copyright (C) 2023-2025 Red Hat Inc.
> >> *
> >> * Authors:
> >> * Hans de Goede <hdegoede at redhat.com>
> >> @@ -18,11 +18,24 @@ namespace libcamera {
> >> struct DebayerParams {
> >> static constexpr unsigned int kRGBLookupSize = 256;
> >>
> >> + struct CcmColumn {
> >> + int16_t r;
> >> + int16_t g;
> >> + int16_t b;
> >> + };
> >> +
> >> using ColorLookupTable = std::array<uint8_t, kRGBLookupSize>;
> >> + using CcmLookupTable = std::array<CcmColumn, kRGBLookupSize>;
> >> + using GammaLookupTable = std::array<uint8_t, kRGBLookupSize>;
> >>
> >> ColorLookupTable red;
> >> ColorLookupTable green;
> >> ColorLookupTable blue;
> >> +
> >> + CcmLookupTable redCcm;
> >> + CcmLookupTable greenCcm;
> >> + CcmLookupTable blueCcm;
> >> + GammaLookupTable gammaLut;
> >> };
> >>
> >> } /* namespace libcamera */
> >> diff --git a/src/ipa/simple/algorithms/lut.cpp b/src/ipa/simple/algorithms/lut.cpp
> >> index e5e995c7..7719aecc 100644
> >> --- a/src/ipa/simple/algorithms/lut.cpp
> >> +++ b/src/ipa/simple/algorithms/lut.cpp
> >> @@ -1,6 +1,6 @@
> >> /* SPDX-License-Identifier: LGPL-2.1-or-later */
> >> /*
> >> - * Copyright (C) 2024, Red Hat Inc.
> >> + * Copyright (C) 2024-2025, Red Hat Inc.
> >> *
> >> * Color lookup tables construction
> >> */
> >> @@ -80,6 +80,11 @@ void Lut::updateGammaTable(IPAContext &context)
> >> context.activeState.gamma.contrast = contrast;
> >> }
> >>
> >> +int16_t Lut::ccmValue(unsigned int i, float ccm) const
> >> +{
> >> + return std::round(i * ccm);
> >> +}
> >> +
> >> void Lut::prepare(IPAContext &context,
> >> [[maybe_unused]] const uint32_t frame,
> >> [[maybe_unused]] IPAFrameContext &frameContext,
> >> @@ -91,28 +96,52 @@ void Lut::prepare(IPAContext &context,
> >> * observed, it's not permanently prone to minor fluctuations or
> >> * rounding errors.
> >> */
> >> - if (context.activeState.gamma.blackLevel != context.activeState.blc.level ||
> >> - context.activeState.gamma.contrast != context.activeState.knobs.contrast)
> >> + const bool gammaUpdateNeeded =
> >> + context.activeState.gamma.blackLevel != context.activeState.blc.level ||
> >> + context.activeState.gamma.contrast != context.activeState.knobs.contrast;
> >> + if (gammaUpdateNeeded)
> >> updateGammaTable(context);
> >>
> >> auto &gains = context.activeState.awb.gains;
> >> auto &gammaTable = context.activeState.gamma.gammaTable;
> >> const unsigned int gammaTableSize = gammaTable.size();
> >> -
> >> - for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++) {
> >> - const double div = static_cast<double>(DebayerParams::kRGBLookupSize) /
> >> - gammaTableSize;
> >> - /* Apply gamma after gain! */
> >> - unsigned int idx;
> >> - idx = std::min({ static_cast<unsigned int>(i * gains.r() / div),
> >> - gammaTableSize - 1 });
> >> - params->red[i] = gammaTable[idx];
> >> - idx = std::min({ static_cast<unsigned int>(i * gains.g() / div),
> >> - gammaTableSize - 1 });
> >> - params->green[i] = gammaTable[idx];
> >> - idx = std::min({ static_cast<unsigned int>(i * gains.b() / div),
> >> - gammaTableSize - 1 });
> >> - params->blue[i] = gammaTable[idx];
> >> + const double div = static_cast<double>(DebayerParams::kRGBLookupSize) /
> >> + gammaTableSize;
> >> +
> >> + if (!context.ccmEnabled) {
> >> + for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++) {
> >> + /* Apply gamma after gain! */
> >> + unsigned int idx;
> >> + idx = std::min({ static_cast<unsigned int>(i * gains.r() / div),
> >> + gammaTableSize - 1 });
> >> + params->red[i] = gammaTable[idx];
> >> + idx = std::min({ static_cast<unsigned int>(i * gains.g() / div),
> >> + gammaTableSize - 1 });
> >> + params->green[i] = gammaTable[idx];
> >> + idx = std::min({ static_cast<unsigned int>(i * gains.b() / div),
> >> + gammaTableSize - 1 });
> >> + params->blue[i] = gammaTable[idx];
> >> + }
> >> + } else if (context.activeState.ccm.changed || gammaUpdateNeeded) {
> >> + Matrix<double, 3, 3> gainCcm = { { gains.r(), 0, 0,
> >> + 0, gains.g(), 0,
> >> + 0, 0, gains.b() } };
> >> + auto ccm = gainCcm * context.activeState.ccm.ccm;
> >> + auto &red = params->redCcm;
> >> + auto &green = params->greenCcm;
> >> + auto &blue = params->blueCcm;
> >> + for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++) {
> >> + red[i].r = ccmValue(i, ccm[0][0]);
> >> + red[i].g = ccmValue(i, ccm[1][0]);
> >> + red[i].b = ccmValue(i, ccm[2][0]);
> >> + green[i].r = ccmValue(i, ccm[0][1]);
> >> + green[i].g = ccmValue(i, ccm[1][1]);
> >> + green[i].b = ccmValue(i, ccm[2][1]);
> >> + blue[i].r = ccmValue(i, ccm[0][2]);
> >> + blue[i].g = ccmValue(i, ccm[1][2]);
> >> + blue[i].b = ccmValue(i, ccm[2][2]);
> >> + params->gammaLut[i] = gammaTable[i / div];
> >> + }
> >> }
> >> }
> >>
> >> diff --git a/src/ipa/simple/algorithms/lut.h b/src/ipa/simple/algorithms/lut.h
> >> index 889f864b..77324800 100644
> >> --- a/src/ipa/simple/algorithms/lut.h
> >> +++ b/src/ipa/simple/algorithms/lut.h
> >> @@ -33,6 +33,7 @@ public:
> >>
> >> private:
> >> void updateGammaTable(IPAContext &context);
> >> + int16_t ccmValue(unsigned int i, float ccm) const;
> >> };
> >>
> >> } /* namespace ipa::soft::algorithms */
> >> diff --git a/src/libcamera/software_isp/debayer.cpp b/src/libcamera/software_isp/debayer.cpp
> >> index 45fe6960..4c84a556 100644
> >> --- a/src/libcamera/software_isp/debayer.cpp
> >> +++ b/src/libcamera/software_isp/debayer.cpp
> >> @@ -23,9 +23,39 @@ namespace libcamera {
> >> * \brief Size of a color lookup table
> >> */
> >>
> >> +/**
> >> + * \struct DebayerParams::CcmColumn
> >> + * \brief Type of a single column of a color correction matrix (CCM)
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::CcmColumn::r
> >> + * \brief Red (first) component of a CCM column
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::CcmColumn::g
> >> + * \brief Green (second) component of a CCM column
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::CcmColumn::b
> >> + * \brief Blue (third) component of a CCM column
> >> + */
> >> +
> >> /**
> >> * \typedef DebayerParams::ColorLookupTable
> >> - * \brief Type of the lookup tables for red, green, blue values
> >> + * \brief Type of the simple lookup tables for red, green, blue values
> >> + */
> >> +
> >> +/**
> >> + * \typedef DebayerParams::CcmLookupTable
> >> + * \brief Type of the CCM lookup tables for red, green, blue values
> >> + */
> >> +
> >> +/**
> >> + * \typedef DebayerParams::GammaLookupTable
> >> + * \brief Type of the gamma lookup tables for CCM
> >> */
> >>
> >> /**
> >> @@ -43,6 +73,26 @@ namespace libcamera {
> >> * \brief Lookup table for blue color, mapping input values to output values
> >> */
> >>
> >> +/**
> >> + * \var DebayerParams::redCcm
> >> + * \brief CCM lookup table for red color, mapping input values to output values
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::greenCcm
> >> + * \brief CCM lookup table for green color, mapping input values to output values
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::blueCcm
> >> + * \brief CCM lookup table for blue color, mapping input values to output values
> >> + */
> >> +
> >> +/**
> >> + * \var DebayerParams::gammaLut
> >> + * \brief Gamma lookup table used with color correction matrix
> >> + */
> >> +
> >> /**
> >> * \class Debayer
> >> * \brief Base debayering class
> >> diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp
> >> index 0cd03a8f..5ddfdcf6 100644
> >> --- a/src/libcamera/software_isp/debayer_cpu.cpp
> >> +++ b/src/libcamera/software_isp/debayer_cpu.cpp
> >> @@ -11,6 +11,7 @@
> >>
> >> #include "debayer_cpu.h"
> >>
> >> +#include <algorithm>
> >> #include <stdlib.h>
> >> #include <sys/ioctl.h>
> >> #include <time.h>
> >> @@ -51,8 +52,12 @@ DebayerCpu::DebayerCpu(std::unique_ptr<SwStatsCpu> stats)
> >> enableInputMemcpy_ = true;
> >>
> >> /* Initialize color lookup tables */
> >> - for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++)
> >> + for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++) {
> >> red_[i] = green_[i] = blue_[i] = i;
> >> + redCcm_[i] = { 1, 0, 0 };
> >> + greenCcm_[i] = { 0, 1, 0 };
> >> + blueCcm_[i] = { 0, 0, 1 };
> >> + }
> >> }
> >>
> >> DebayerCpu::~DebayerCpu() = default;
> >> @@ -62,12 +67,24 @@ DebayerCpu::~DebayerCpu() = default;
> >> const pixel_t *curr = (const pixel_t *)src[1] + xShift_; \
> >> const pixel_t *next = (const pixel_t *)src[2] + xShift_;
> >>
> >> -#define STORE_PIXEL(b, g, r) \
> >> - *dst++ = blue_[b]; \
> >> - *dst++ = green_[g]; \
> >> - *dst++ = red_[r]; \
> >> - if constexpr (addAlphaByte) \
> >> - *dst++ = 255; \
> >> +#define GAMMA(value) \
> >> + *dst++ = gammaLut_[std::clamp(value, 0, static_cast<int>(gammaLut_.size()) - 1)]
> >> +
> >> +#define STORE_PIXEL(b_, g_, r_) \
> >> + if constexpr (ccmEnabled) { \
> >> + const DebayerParams::CcmColumn &blue = blueCcm_[b_]; \
> >> + const DebayerParams::CcmColumn &green = greenCcm_[g_]; \
> >> + const DebayerParams::CcmColumn &red = redCcm_[r_]; \
> >> + GAMMA(blue.r + blue.g + blue.b); \
> >> + GAMMA(green.r + green.g + green.b); \
> >> + GAMMA(red.r + red.g + red.b); \
> >> + } else { \
> >> + *dst++ = blue_[b_]; \
> >> + *dst++ = green_[g_]; \
> >> + *dst++ = red_[r_]; \
> >> + } \
> >> + if constexpr (addAlphaByte) \
> >> + *dst++ = 255; \
> >> x++;
> >>
> >> /*
> >> @@ -757,6 +774,10 @@ void DebayerCpu::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output
> >> green_ = params.green;
> >> red_ = swapRedBlueGains_ ? params.blue : params.red;
> >> blue_ = swapRedBlueGains_ ? params.red : params.blue;
> >> + greenCcm_ = params.greenCcm;
> >> + redCcm_ = swapRedBlueGains_ ? params.blueCcm : params.redCcm;
> >> + blueCcm_ = swapRedBlueGains_ ? params.redCcm : params.blueCcm;
> >> + gammaLut_ = params.gammaLut;
> >>
> >> /* Copy metadata from the input buffer */
> >> FrameMetadata &metadata = output->_d()->metadata();
> >> diff --git a/src/libcamera/software_isp/debayer_cpu.h b/src/libcamera/software_isp/debayer_cpu.h
> >> index 21c08a2d..9f73a2fd 100644
> >> --- a/src/libcamera/software_isp/debayer_cpu.h
> >> +++ b/src/libcamera/software_isp/debayer_cpu.h
> >> @@ -141,6 +141,10 @@ private:
> >> DebayerParams::ColorLookupTable red_;
> >> DebayerParams::ColorLookupTable green_;
> >> DebayerParams::ColorLookupTable blue_;
> >> + DebayerParams::CcmLookupTable redCcm_;
> >> + DebayerParams::CcmLookupTable greenCcm_;
> >> + DebayerParams::CcmLookupTable blueCcm_;
> >> + DebayerParams::GammaLookupTable gammaLut_;
> >> debayerFn debayer0_;
> >> debayerFn debayer1_;
> >> debayerFn debayer2_;
>
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