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charset=\"utf-8\"", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "From": "Javier Tia <floss@jetm.me>", "To": "libcamera-devel@lists.libcamera.org", "Date": "Wed, 06 May 2026 15:45:28 -0600", "Subject": "[PATCH v5 0/3] ipa: simple: Proportional AGC and statistics\n\tnormalization", "Cc": "mzamazal@redhat.com, barnabas.pocze@ideasonboard.com,\n\tkieran.bingham@ideasonboard.com, johannes.goede@oss.qualcomm.com", "In-Reply-To": "<20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me>", "References": "<20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me>", "Message-ID": "<177810597783.688418.1631246733707368646@jetm.me>", "X-BeenThere": "libcamera-devel@lists.libcamera.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<libcamera-devel.lists.libcamera.org>", "List-Unsubscribe": "<https://lists.libcamera.org/options/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=unsubscribe>", "List-Archive": "<https://lists.libcamera.org/pipermail/libcamera-devel/>", "List-Post": "<mailto:libcamera-devel@lists.libcamera.org>", "List-Help": "<mailto:libcamera-devel-request@lists.libcamera.org?subject=help>", "List-Subscribe": "<https://lists.libcamera.org/listinfo/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=subscribe>", "Errors-To": "libcamera-devel-bounces@lists.libcamera.org", "Sender": "\"libcamera-devel\" <libcamera-devel-bounces@lists.libcamera.org>" }, "content": "The AGC in the simple pipeline uses a fixed ~10% step per frame regardless\nof how far the current exposure is from the target. With a hysteresis dead\nband of only +/-4%, the controller overshoots near the optimal value,\ncausing visible brightness oscillation (flicker).\n\nThis series replaces the bang-bang controller with a proportional one\n(patch 1/3), fixes a bit-depth mismatch in the statistics sums used by\nAWB (patch 2/3), and adds the OV2740 black level calibration needed for\ncorrect BLC subtraction (patch 3/3).\n\nTested on OV2740 behind Intel IPU6 ISYS (ThinkPad X1 Carbon Gen 10).\nA 40-frame capture with all three patches shows smooth monotonic brightness\nconvergence from frame 4 onwards with no oscillation.\n\nChanges since v4:\n- Patch 1/3: Added kExpMaxStep = 0.15 to clamp the proportional step,\n bounding corrections to +/-15% even when the scene changes dramatically.\n This addresses Barnabas's question on v4 about large-error behavior.\n- Patch 2/3: Rebased; diff context updated for the multi-threading refactor\n in swstats_cpu (6e53e72e), which restructured finishFrame() to aggregate\n from a stats_ vector before applying the shift. No functional change.\n\nRegarding Kieran's question on patch 1/3 (gain model): the proportional\nstep `again * factor` has the same linearity assumption as the old fixed\nstep `again * 11/10`. Both multiply the current register value by a\nscalar. For devices without a calibrated gain model the register value\nis already used as a linear proxy in the original code. This change only\naffects the step magnitude, not the direction logic or gain model\nassumption. Devices without a gain model should behave the same or better.\n\nRegarding Kieran's question on whether 3/3 is needed for the flicker fix:\npatch 1/3 alone cures the flicker. Patch 3/3 improves AWB color accuracy\nby providing the correct black level baseline (BLC=16) for channel gain\ncalculation, but it is independent of the oscillation fix.\n\nLink to v4: https://lore.kernel.org/libcamera-devel/20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me/\n\nJavier Tia (3):\n ipa: simple: agc: Replace bang-bang controller with proportional\n libcamera: software_isp: Normalize statistics sums to 8-bit\n ipa: libipa: camera_sensor_helper: Add OV2740 black level\n\n .../internal/software_isp/swstats_cpu.h | 1 +\n src/ipa/libipa/camera_sensor_helper.cpp | 2 +\n src/ipa/simple/algorithms/agc.cpp | 73 +++++++++++++------\n src/libcamera/software_isp/swstats_cpu.cpp | 9 +++\n 4 files changed, 61 insertions(+), 24 deletions(-)" }