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libcamera: simple: Fix black level offsets in AWB

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The black level offset subtracted in AWB is wrong.  It assumes that the
stats contain sums of the individual colour pixels.  But they actually
contain sums of the colour channels of larger "superpixels" consisting
of the individual colour pixels.  Each of the RGB colour values and the
computed luminosity (a histogram entry) are added once to the stats per
such a superpixel.  This means the offset computed from the black level
and the number of pixels should be used as it is, not divided.

The patch fixes the subtracted offset.  Since the evaluation is the same
for all the three colours now, the individual class variables are
replaced with a single RGB variable.

Fixes: 4e13c6f55b ("Honor black level in AWB")
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Robert Mader <robert.mader@collabora.com>
Tested-by: Robert Mader <robert.mader@collabora.com>
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Milan Zamazal
2026-01-27 21:47:11 +01:00
committed by Kieran Bingham
parent 10e4e5ba1e
commit 07240afa12
3 changed files with 17 additions and 23 deletions
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14
src/ipa/simple/algorithms/awb.cpp
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@@ -1,6 +1,6 @@
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2024, Red Hat Inc.
* Copyright (C) 2024-2026 Red Hat Inc.
*
* Auto white balance
*/
@@ -73,9 +73,11 @@ void Awb::process(IPAContext &context,
histogram.begin(), histogram.end(), uint64_t(0));
const uint64_t offset = blackLevel * nPixels;
const uint64_t minValid = 1;
const uint64_t sumR = stats->sumR_ > offset / 4 ? stats->sumR_ - offset / 4 : minValid;
const uint64_t sumG = stats->sumG_ > offset / 2 ? stats->sumG_ - offset / 2 : minValid;
const uint64_t sumB = stats->sumB_ > offset / 4 ? stats->sumB_ - offset / 4 : minValid;
/*
* Make sure the sums are at least minValid, while preventing unsigned
* integer underflow.
*/
const RGB<uint64_t> sum = stats->sum_.max(offset + minValid) - offset;
/*
* Calculate red and blue gains for AWB.
@@ -83,9 +85,9 @@ void Awb::process(IPAContext &context,
*/
auto &gains = context.activeState.awb.gains;
gains = { {
sumR <= sumG / 4 ? 4.0f : static_cast<float>(sumG) / sumR,
sum.r() <= sum.g() / 4 ? 4.0f : static_cast<float>(sum.g()) / sum.r(),
1.0,
sumB <= sumG / 4 ? 4.0f : static_cast<float>(sumG) / sumB,
sum.b() <= sum.g() / 4 ? 4.0f : static_cast<float>(sum.g()) / sum.b(),
} };
RGB<double> rgbGains{ { 1 / gains.r(), 1 / gains.g(), 1 / gains.b() } };