[PATCH] libcamera: software_isp: Add saturation control
Milan Zamazal
mzamazal at redhat.com
Mon Apr 14 16:49:58 CEST 2025
Kieran Bingham <kieran.bingham at ideasonboard.com> writes:
> Quoting Milan Zamazal (2025-04-14 14:15:38)
>> Hi Kieran,
>>
>
>> thank you for review.
>>
>> Kieran Bingham <kieran.bingham at ideasonboard.com> writes:
>>
>> > Quoting Milan Zamazal (2025-04-07 09:58:02)
>> >> Saturation control is added on top of the colour correction matrix. A
>> >> way of saturation adjustment that can be fully integrated into the
>> >
>> >> colour correction matrix is used. The control is available only if Ccm
>> >> algorithm is enabled.
>> >>
>> >> The control uses 0.0-2.0 value range, with 1.0 being unmodified
>> >> saturation, 0.0 full desaturation and 2.0 quite saturated.
>> >>
>> >> The matrix for saturation adjustment is taken from
>> >> https://www.graficaobscura.com/matrix/index.html. The colour correction
>> >> matrix is applied before gamma and the given matrix is suitable for such
>> >> a case. Alternatively, the transformation used in libcamera rpi ccm.cpp
>> >> could be used.
>> >>
>> >> Signed-off-by: Milan Zamazal <mzamazal at redhat.com>
>> >> ---
>> >> src/ipa/simple/algorithms/ccm.cpp | 57 +++++++++++++++++++++++++++++--
>> >> src/ipa/simple/algorithms/ccm.h | 11 ++++++
>> >> src/ipa/simple/ipa_context.h | 4 +++
>> >> 3 files changed, 69 insertions(+), 3 deletions(-)
>> >>
>> >> diff --git a/src/ipa/simple/algorithms/ccm.cpp b/src/ipa/simple/algorithms/ccm.cpp
>> >> index d5ba928d..2700a247 100644
>> >> --- a/src/ipa/simple/algorithms/ccm.cpp
>> >> +++ b/src/ipa/simple/algorithms/ccm.cpp
>> >> @@ -3,7 +3,7 @@
>> >> * Copyright (C) 2024, Ideas On Board
>> >> * Copyright (C) 2024-2025, Red Hat Inc.
>> >> *
>> >> - * Color correction matrix
>> >> + * Color correction matrix + saturation
>> >> */
>> >>
>> >> #include "ccm.h"
>> >> @@ -13,6 +13,8 @@
>> >>
>> >> #include <libcamera/control_ids.h>
>> >>
>> >> +#include "libcamera/internal/matrix.h"
>> >> +
>> >> namespace {
>> >>
>> >> constexpr unsigned int kTemperatureThreshold = 100;
>> >> @@ -35,28 +37,73 @@ int Ccm::init([[maybe_unused]] IPAContext &context, const YamlObject &tuningData
>> >> }
>> >>
>> >> context.ccmEnabled = true;
>> >> + context.ctrlMap[&controls::Saturation] = ControlInfo(0.0f, 2.0f, 1.0f);
>> >> +
>> >> + return 0;
>> >> +}
>> >> +
>> >> +int Ccm::configure(IPAContext &context,
>> >> + [[maybe_unused]] const IPAConfigInfo &configInfo)
>> >> +{
>> >> + context.activeState.knobs.saturation = std::optional<double>();
>> >>
>> >> return 0;
>> >> }
>> >>
>> >> +void Ccm::queueRequest(typename Module::Context &context,
>> >> + [[maybe_unused]] const uint32_t frame,
>> >> + [[maybe_unused]] typename Module::FrameContext &frameContext,
>> >> + const ControlList &controls)
>> >> +{
>> >> + const auto &saturation = controls.get(controls::Saturation);
>> >> + if (saturation.has_value()) {
>> >> + context.activeState.knobs.saturation = saturation;
>> >> + LOG(IPASoftCcm, Debug) << "Setting saturation to " << saturation.value();
>> >> + }
>> >> +}
>> >> +
>> >> +void Ccm::updateSaturation(Matrix<float, 3, 3> &ccm, float saturation)
>> >> +{
>> >> + /*
>> >> + * See https://www.graficaobscura.com/matrix/index.html.
>> >
>> > Looks like it would be easy to add a brightness control too after this.
>>
>> Yes, when CCM is used, it's easy to add brightness. And when CCM is not
>> used, it's easy too, applying it when making the LUT values -- this is
>> important for CPU ISP when CCM is not used (having to use CCM just to
>> adjust brightness would be overkill).
>
> Aha, then indeed lets just apply it directly to the LUT (later) :-)
>
>>
>> >> + * This is applied before gamma thus a matrix for linear RGB must be used.
>> >> + * The saturation range is 0..2, with 1 being an unchanged saturation and 0
>> >> + * no saturation (monochrome).
>> >> + */
>> >> + constexpr float r = 0.3086;
>> >> + constexpr float g = 0.6094;
>> >> + constexpr float b = 0.0820;
>> >
>> > it would be interesting to dig into where these numbers are derived
>> > from exactly ...
>>
>> I guess some educated magic, similarly to other luminance related
>> conversions.
>>
>> > https://dsp.stackexchange.com/questions/27599/how-is-the-luminance-vector-calculated-for-these-linear-matrix-transforms
>> > seems to report others have looked, but I don't see a direct answer yet
>> > (but I won't dig deep) ...
>> >
>> > And the referenced article is quite helpful.
>> >
>> > As this is the 'luminance' vector - I wonder if writing it as
>> > RGB<float> luminance = { 0.3086, 0.6094, 0.0820 };
>> >
>> > makes sense...
>> >
>> >> + const float s1 = 1.0 - saturation;
>> >> + ccm = ccm * Matrix<float, 3, 3>{ { s1 * r + saturation, s1 * g, s1 * b,
>> >> + s1 * r, s1 * g + saturation, s1 * b,
>> >> + s1 * r, s1 * g, s1 * b + saturation } };
This multiplication should be also performed in the reverse order.
>> >
>> > but that would become much more terse ... so I'm not sure it's worth it
>> > here? Or would it then be more explicitly readable like the
>> > applySaturation in RPi?
>>
>> I'll try and let's see.
>>
>> >> +}
>> >> +
>> >> void Ccm::prepare(IPAContext &context, const uint32_t frame,
>> >> IPAFrameContext &frameContext, [[maybe_unused]] DebayerParams *params)
>> >> {
>> >> + auto &saturation = context.activeState.knobs.saturation;
>> >> +
>> >> const unsigned int ct = context.activeState.awb.temperatureK;
>> >>
>> >> - /* Change CCM only on bigger temperature changes. */
>> >> + /* Change CCM only on saturation or bigger temperature changes. */
>> >> if (frame > 0 &&
>> >> - utils::abs_diff(ct, lastCt_) < kTemperatureThreshold) {
>> >> + utils::abs_diff(ct, lastCt_) < kTemperatureThreshold &&
>> >> + saturation == lastSaturation_) {
>> >> frameContext.ccm.ccm = context.activeState.ccm.ccm;
>> >> context.activeState.ccm.changed = false;
>> >> return;
>> >> }
>> >>
>> >> lastCt_ = ct;
>> >> + lastSaturation_ = saturation;
>> >> Matrix<float, 3, 3> ccm = ccm_.getInterpolated(ct);
>> >> + if (saturation)
>> >> + updateSaturation(ccm, saturation.value());
>> >>
>> >> context.activeState.ccm.ccm = ccm;
>> >> frameContext.ccm.ccm = ccm;
>> >> + frameContext.saturation = saturation;
>> >> context.activeState.ccm.changed = true;
>> >> }
>> >>
>> >> @@ -67,6 +114,10 @@ void Ccm::process([[maybe_unused]] IPAContext &context,
>> >> ControlList &metadata)
>> >> {
>> >> metadata.set(controls::ColourCorrectionMatrix, frameContext.ccm.ccm.data());
>> >> +
>> >> + const auto &saturation = frameContext.saturation;
>> >> + if (saturation)
>> >> + metadata.set(controls::Saturation, saturation.value());
>> >
>> > This matches what we currently do for Contrast, but I wonder if we
>> > should report a metadata of '1.0' for both Contrast and Saturation if
>> > they aren't set ... as that's what the 'state' is/should be ?
>>
>> I don't have an opinion on this, both of "no saturation request -> no
>> metadata" and "no saturation request -> the corresponding default value
>> in metadata" make sense to me.
>>
>> > Anyway, I wouldn't block this patch on that - as it would be on top for
>> > both controls...
>> >
>> > Tested-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>> >
>> > Though, while it's functional - looking at the resulting image in
>> > camshark, I think I would expect a saturation of 0.0 to be 'greyscale' -
>> > with all pixels having roughly the same r=g=b - and I don't think that's
>> > the case ... It looks like there's definitely a bias against green. It
>> > looks like R=B, but G is always slightly less by at least ~20% ? ...
>> > leaving the image looking slightly tinted purple.
>>
>> Oh, now, under daylight, I get a prominent purple tint too.
>>
>> > That could be because I'm running an untuned/identity matrix for CCM
>> > perhaps? or is it because white balance needs to be taken into account ?
>>
>> No, it's a math mistake I did in CCM patches. White balance must be
>> applied before CCM. Let C be the CCM, W the AWB gains CCM-like matrix,
>> and P the pixel RGB vector. I thought "let's apply C after W" and
>> computed (W * C) * P. Which is wrong, to apply C after W means
>> C * (W * P) = (C * W) * P. The last matrix applied must be the first
>> one in the multiplication. When I swap the multiplication in
>> src/ipa/simple/algorithms/lut.cpp from
>>
>> auto ccm = gainCcm * context.activeState.ccm.ccm;
>>
>> to
>>
>> auto ccm = context.activeState.ccm.ccm * gainCcm;
>>
>> it gets desaturated as it should be (there cannot be any colour cast
>> when desaturation is applied correctly, regardless of sensor
>> calibration). Maybe this will also explain and improve the colour casts
>> I previously experienced when experimenting with my sensor CCMs from
>> other pipelines.
>>
>> > But G = (RB-20%) doesn't sound like white balance to me at the moment...
>
> aha, so maybe it is ;-)
>
> Great, well if that's explained ... we have a path forwards. Does it
> impact this patch much? Would it help to merge this first? or fix the
> CCM then rebase this one ?
The latter. I'll post the CCM fix separately. The saturation patch
needs a multiplication order fix too and I'd like to simplify
updateSaturation() a bit; I'll post v2.
Then there is a question what to do about saturation + contrast. I
believe contrast should be applied between sensor-CCM and saturation but
this would be too expensive on a CPU.
> I think the colour tint is the only thing stopping me from adding a tag,
> and if that's clarified, then for Saturation:
>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>
> If you respin with the calculation split out in Ccm::updateSaturation()
> you can still collect the tag I think. (perhaps there's a new series
> with the above change and the color fix on the way?)
>
> --
> Kieran
>
>> >
>> >> }
>> >>
>> >> REGISTER_IPA_ALGORITHM(Ccm, "Ccm")
>> >> diff --git a/src/ipa/simple/algorithms/ccm.h b/src/ipa/simple/algorithms/ccm.h
>> >> index f4e2b85b..2c5d2170 100644
>> >> --- a/src/ipa/simple/algorithms/ccm.h
>> >> +++ b/src/ipa/simple/algorithms/ccm.h
>> >> @@ -7,6 +7,8 @@
>> >>
>> >> #pragma once
>> >>
>> >> +#include <optional>
>> >> +
>> >> #include "libcamera/internal/matrix.h"
>> >>
>> >> #include <libipa/interpolator.h>
>> >> @@ -24,6 +26,12 @@ public:
>> >> ~Ccm() = default;
>> >>
>> >> int init(IPAContext &context, const YamlObject &tuningData) override;
>> >> + int configure(IPAContext &context,
>> >> + const IPAConfigInfo &configInfo) override;
>> >> + void queueRequest(typename Module::Context &context,
>> >> + const uint32_t frame,
>> >> + typename Module::FrameContext &frameContext,
>> >> + const ControlList &controls) override;
>> >> void prepare(IPAContext &context,
>> >> const uint32_t frame,
>> >> IPAFrameContext &frameContext,
>> >> @@ -34,7 +42,10 @@ public:
>> >> ControlList &metadata) override;
>> >>
>> >> private:
>> >> + void updateSaturation(Matrix<float, 3, 3> &ccm, float saturation);
>> >> +
>> >> unsigned int lastCt_;
>> >> + std::optional<float> lastSaturation_;
>> >> Interpolator<Matrix<float, 3, 3>> ccm_;
>> >> };
>> >>
>> >> diff --git a/src/ipa/simple/ipa_context.h b/src/ipa/simple/ipa_context.h
>> >> index 88cc6c35..56792981 100644
>> >> --- a/src/ipa/simple/ipa_context.h
>> >> +++ b/src/ipa/simple/ipa_context.h
>> >> @@ -63,6 +63,7 @@ struct IPAActiveState {
>> >> struct {
>> >> /* 0..2 range, 1.0 = normal */
>> >> std::optional<double> contrast;
>> >> + std::optional<double> saturation;
>> >> } knobs;
>> >> };
>> >>
>> >> @@ -75,11 +76,14 @@ struct IPAFrameContext : public FrameContext {
>> >> int32_t exposure;
>> >> double gain;
>> >> } sensor;
>> >> +
>> >> struct {
>> >> double red;
>> >> double blue;
>> >> } gains;
>> >> +
>> >> std::optional<double> contrast;
>> >> + std::optional<double> saturation;
>> >> };
>> >>
>> >> struct IPAContext {
>> >> --
>> >> 2.49.0
>> >>
>>
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