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ipa: rpi: agc: Change handling of colour gains less than 1

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Previously these were handled in the AGC/AEC exposure update
calculations by explicitly driving a higher digital gain to "cancel
out" any colour gains that were less than 1.

Now we're ignoring this in the AGC and leaving it to the IPA code to
normalise all the gains so that the smallest is 1. We don't regard
this as a "real" increase because one of the colour channels (just not
necessarily the green one) still gets the minimum gain possible.

We do, however, update the statistics calculations so that they
reflect any such digital gain increase, so that images are driven to
the correct level.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
David Plowman
2025-07-21 08:47:21 +01:00
committed by Kieran Bingham
parent 9c082483f4
commit 42562d6d33
3 changed files with 54 additions and 39 deletions
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src/ipa/rpi/pisp/pisp.cpp
+20 -6
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@@ -521,10 +521,24 @@ void IpaPiSP::applyWBG(const AwbStatus *awbStatus, const AgcPrepareStatus *agcPr
pisp_wbg_config wbg;
pisp_fe_rgby_config rgby = {};
double dg = agcPrepareStatus ? agcPrepareStatus->digitalGain : 1.0;
double minColourGain = std::min({ awbStatus->gainR, awbStatus->gainG, awbStatus->gainB, 1.0 });
/* The 0.1 here doesn't mean much, but just stops arithmetic errors and extreme behaviour. */
double extraGain = 1.0 / std::max({ minColourGain, 0.1 });
wbg.gain_r = clampField(dg * awbStatus->gainR, 14, 10);
wbg.gain_g = clampField(dg * awbStatus->gainG, 14, 10);
wbg.gain_b = clampField(dg * awbStatus->gainB, 14, 10);
/*
* Apply an extra gain of 1 / minColourGain so as not to apply < 1 gains to any
* channels (which would cause saturated pixels to go cyan or magenta).
* Doing this doesn't really apply more gain than necessary, because one of the
* channels is always getting the minimum gain possible. For this reason we also
* don't change the values that we report externally.
*/
double gainR = awbStatus->gainR * extraGain;
double gainG = awbStatus->gainG * extraGain;
double gainB = awbStatus->gainB * extraGain;
wbg.gain_r = clampField(dg * gainR, 14, 10);
wbg.gain_g = clampField(dg * gainG, 14, 10);
wbg.gain_b = clampField(dg * gainB, 14, 10);
/*
* The YCbCr conversion block should contain the appropriate YCbCr
@@ -535,9 +549,9 @@ void IpaPiSP::applyWBG(const AwbStatus *awbStatus, const AgcPrepareStatus *agcPr
be_->GetYcbcr(csc);
/* The CSC coefficients already have the << 10 scaling applied. */
rgby.gain_r = clampField(csc.coeffs[0] * awbStatus->gainR, 14);
rgby.gain_g = clampField(csc.coeffs[1] * awbStatus->gainG, 14);
rgby.gain_b = clampField(csc.coeffs[2] * awbStatus->gainB, 14);
rgby.gain_r = clampField(csc.coeffs[0] * gainR, 14);
rgby.gain_g = clampField(csc.coeffs[1] * gainG, 14);
rgby.gain_b = clampField(csc.coeffs[2] * gainB, 14);
LOG(IPARPI, Debug) << "Applying WB R: " << awbStatus->gainR << " B: "
<< awbStatus->gainB;