[v8,10/10] libcamera: software_isp: Apply CCM in debayering

23045 diff mbox series

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 g1 b1]   [r]
  [r2 g2 b2] * [g]
  [r3 g3 b3]   [b]

The CCM matrix (the left side of the multiplication) is constant during
single frame processing, while the input pixel (the right 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.

Because the changing part is the pixel value with three color elements,
only three dynamic table lookups are needed.  We use three lookup tables
to represent the multiplied matrix values, each of the tables
corresponding to the given matrix column and pixel color.

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@redhat.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 .../internal/software_isp/debayer_params.h    | 36 ++++++++++--
 src/ipa/simple/algorithms/lut.cpp             | 53 +++++++++++++----
 src/ipa/simple/algorithms/lut.h               |  1 +
 src/libcamera/software_isp/debayer.cpp        | 57 ++++++++++++++++++-
 src/libcamera/software_isp/debayer_cpu.cpp    | 53 +++++++++++++----
 src/libcamera/software_isp/debayer_cpu.h      | 10 +++-
 6 files changed, 177 insertions(+), 33 deletions(-)

Quoting Milan Zamazal (2025-03-26 09:08:47)
> 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 g1 b1]   [r]
>   [r2 g2 b2] * [g]
>   [r3 g3 b3]   [b]
> 
> The CCM matrix (the left side of the multiplication) is constant during
> single frame processing, while the input pixel (the right 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.
> 
> Because the changing part is the pixel value with three color elements,
> only three dynamic table lookups are needed.  We use three lookup tables
> to represent the multiplied matrix values, each of the tables
> corresponding to the given matrix column and pixel color.
> 
> 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@redhat.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

> ---
>  .../internal/software_isp/debayer_params.h    | 36 ++++++++++--
>  src/ipa/simple/algorithms/lut.cpp             | 53 +++++++++++++----
>  src/ipa/simple/algorithms/lut.h               |  1 +
>  src/libcamera/software_isp/debayer.cpp        | 57 ++++++++++++++++++-
>  src/libcamera/software_isp/debayer_cpu.cpp    | 53 +++++++++++++----
>  src/libcamera/software_isp/debayer_cpu.h      | 10 +++-
>  6 files changed, 177 insertions(+), 33 deletions(-)
> 
> diff --git a/include/libcamera/internal/software_isp/debayer_params.h b/include/libcamera/internal/software_isp/debayer_params.h
> index 7d8fdd48..217cd5d9 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@redhat.com>
> @@ -18,11 +18,37 @@ namespace libcamera {
>  struct DebayerParams {
>         static constexpr unsigned int kRGBLookupSize = 256;
>  
> -       using ColorLookupTable = std::array<uint8_t, kRGBLookupSize>;
> +       struct CcmColumn {
> +               int16_t r;
> +               int16_t g;
> +               int16_t b;
> +       };
>  
> -       ColorLookupTable red;
> -       ColorLookupTable green;
> -       ColorLookupTable blue;
> +       using LookupTable = std::array<uint8_t, kRGBLookupSize>;
> +       using CcmLookupTable = std::array<CcmColumn, kRGBLookupSize>;
> +
> +       /*
> +        * Color lookup tables when CCM is not used.
> +        *
> +        * Each color of a debayered pixel is amended by the corresponding
> +        * value in the given table.
> +        */
> +       LookupTable red;
> +       LookupTable green;
> +       LookupTable blue;
> +
> +       /*
> +        * Color and gamma lookup tables when CCM is used.
> +        *
> +        * Each of the CcmLookupTable's corresponds to a CCM column; together they
> +        * make a complete 3x3 CCM lookup table. The CCM is applied on debayered
> +        * pixels and then the gamma lookup table is used to set the resulting
> +        * values of all the three colors.
> +        */
> +       CcmLookupTable redCcm;
> +       CcmLookupTable greenCcm;
> +       CcmLookupTable blueCcm;
> +       LookupTable gammaLut;
>  };
>  
>  } /* namespace libcamera */
> diff --git a/src/ipa/simple/algorithms/lut.cpp b/src/ipa/simple/algorithms/lut.cpp
> index 3a3daed7..a06cdeba 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,
> @@ -91,22 +96,46 @@ 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! */
> -               const RGB<float> lutGains = (gains * i / div).min(gammaTableSize - 1);
> -               params->red[i] = gammaTable[static_cast<unsigned int>(lutGains.r())];
> -               params->green[i] = gammaTable[static_cast<unsigned int>(lutGains.g())];
> -               params->blue[i] = gammaTable[static_cast<unsigned int>(lutGains.b())];
> +       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! */
> +                       const RGB<float> lutGains = (gains * i / div).min(gammaTableSize - 1);
> +                       params->red[i] = gammaTable[static_cast<unsigned int>(lutGains.r())];
> +                       params->green[i] = gammaTable[static_cast<unsigned int>(lutGains.g())];
> +                       params->blue[i] = gammaTable[static_cast<unsigned int>(lutGains.b())];
> +               }
> +       } else if (context.activeState.ccm.changed || gammaUpdateNeeded) {
> +               Matrix<float, 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 34e42201..e9e18c48 100644
> --- a/src/libcamera/software_isp/debayer.cpp
> +++ b/src/libcamera/software_isp/debayer.cpp
> @@ -1,7 +1,7 @@
>  /* SPDX-License-Identifier: LGPL-2.1-or-later */
>  /*
>   * Copyright (C) 2023, Linaro Ltd
> - * Copyright (C) 2023, 2024 Red Hat Inc.
> + * Copyright (C) 2023-2025 Red Hat Inc.
>   *
>   * Authors:
>   * Hans de Goede <hdegoede@redhat.com>
> @@ -24,8 +24,39 @@ namespace libcamera {
>   */
>  
>  /**
> - * \typedef DebayerParams::ColorLookupTable
> - * \brief Type of the lookup tables for red, green, blue values
> + * \struct DebayerParams::CcmColumn
> + * \brief Type of a single column of a color correction matrix (CCM)
> + *
> + * When multiplying an input pixel, columns in the CCM correspond to the red,
> + * green or blue component of input pixel values, while rows correspond to the
> + * red, green or blue components of the output pixel values. The members of the
> + * CcmColumn structure are named after the colour components of the output pixel
> + * values they correspond to.
> + */
> +
> +/**
> + * \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::LookupTable
> + * \brief Type of the lookup tables for single lookup values
> + */
> +
> +/**
> + * \typedef DebayerParams::CcmLookupTable
> + * \brief Type of the CCM lookup tables for red, green, blue values
>   */
>  
>  /**
> @@ -43,6 +74,26 @@ namespace libcamera {
>   * \brief Lookup table for blue color, mapping input values to output values
>   */
>  
> +/**
> + * \var DebayerParams::redCcm
> + * \brief Lookup table for the CCM red column, mapping input values to output values
> + */
> +
> +/**
> + * \var DebayerParams::greenCcm
> + * \brief Lookup table for the CCM green column, mapping input values to output values
> + */
> +
> +/**
> + * \var DebayerParams::blueCcm
> + * \brief Lookup table for the CCM blue column, 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..66f6038c 100644
> --- a/src/libcamera/software_isp/debayer_cpu.cpp
> +++ b/src/libcamera/software_isp/debayer_cpu.cpp
> @@ -1,7 +1,7 @@
>  /* SPDX-License-Identifier: LGPL-2.1-or-later */
>  /*
>   * Copyright (C) 2023, Linaro Ltd
> - * Copyright (C) 2023, Red Hat Inc.
> + * Copyright (C) 2023-2025 Red Hat Inc.
>   *
>   * Authors:
>   * Hans de Goede <hdegoede@redhat.com>
> @@ -11,9 +11,11 @@
>  
>  #include "debayer_cpu.h"
>  
> +#include <algorithm>
>  #include <stdlib.h>
>  #include <sys/ioctl.h>
>  #include <time.h>
> +#include <utility>
>  
>  #include <linux/dma-buf.h>
>  
> @@ -51,8 +53,12 @@ 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] = { static_cast<int16_t>(i), 0, 0 };
> +               greenCcm_[i] = { 0, static_cast<int16_t>(i), 0 };
> +               blueCcm_[i] = { 0, 0, static_cast<int16_t>(i) };
> +       }
>  }
>  
>  DebayerCpu::~DebayerCpu() = default;
> @@ -62,12 +68,24 @@ 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.b + green.b + red.b);                       \
> +               GAMMA(blue.g + green.g + red.g);                       \
> +               GAMMA(blue.r + green.r + red.r);                       \
> +       } else {                                                       \
> +               *dst++ = blue_[b_];                                    \
> +               *dst++ = green_[g_];                                   \
> +               *dst++ = red_[r_];                                     \
> +       }                                                              \
> +       if constexpr (addAlphaByte)                                    \
> +               *dst++ = 255;                                          \
>         x++;
>  
>  /*
> @@ -755,8 +773,23 @@ void DebayerCpu::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output
>                 dmaSyncers.emplace_back(plane.fd, DmaSyncer::SyncType::Write);
>  
>         green_ = params.green;
> -       red_ = swapRedBlueGains_ ? params.blue : params.red;
> -       blue_ = swapRedBlueGains_ ? params.red : params.blue;
> +       greenCcm_ = params.greenCcm;
> +       if (swapRedBlueGains_) {
> +               red_ = params.blue;
> +               blue_ = params.red;
> +               redCcm_ = params.blueCcm;
> +               blueCcm_ = params.redCcm;
> +               for (unsigned int i = 0; i < 256; i++) {
> +                       std::swap(redCcm_[i].r, redCcm_[i].b);
> +                       std::swap(blueCcm_[i].r, blueCcm_[i].b);
> +               }
> +       } else {
> +               red_ = params.red;
> +               blue_ = params.blue;
> +               redCcm_ = params.redCcm;
> +               blueCcm_ = 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..926195e9 100644
> --- a/src/libcamera/software_isp/debayer_cpu.h
> +++ b/src/libcamera/software_isp/debayer_cpu.h
> @@ -138,9 +138,13 @@ private:
>         /* Max. supported Bayer pattern height is 4, debayering this requires 5 lines */
>         static constexpr unsigned int kMaxLineBuffers = 5;
>  
> -       DebayerParams::ColorLookupTable red_;
> -       DebayerParams::ColorLookupTable green_;
> -       DebayerParams::ColorLookupTable blue_;
> +       DebayerParams::LookupTable red_;
> +       DebayerParams::LookupTable green_;
> +       DebayerParams::LookupTable blue_;
> +       DebayerParams::CcmLookupTable redCcm_;
> +       DebayerParams::CcmLookupTable greenCcm_;
> +       DebayerParams::CcmLookupTable blueCcm_;
> +       DebayerParams::LookupTable gammaLut_;
>         debayerFn debayer0_;
>         debayerFn debayer1_;
>         debayerFn debayer2_;
> -- 
> 2.49.0
>