[v4,0/3] Simple pipeline: proportional AGC, AWB stats fix, OV2740 black level
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Message ID 20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me
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  • Simple pipeline: proportional AGC, AWB stats fix, OV2740 black level
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Javier Tia March 6, 2026, 6:46 p.m. UTC 
This series fixes AGC oscillation and an AWB statistics bug in the
Simple pipeline, and adds the OV2740 black level to the sensor helper.

Patch 1 replaces the fixed 10% bang-bang step in the AGC with a
proportional controller where step size scales with the MSV error.
This eliminates the brightness flicker observed on sensors with
non-trivial control latency (tested on OV2740 behind Intel
IPU6/IVSC).

Patch 2 fixes a bit-depth mismatch in the statistics gathering.
The SWSTATS_ACCUMULATE_LINE_STATS() macro divides the luminance value
for the histogram to normalize it to 8-bit range, but does not apply
the same normalization to the RGB sums. For 10-bit and 12-bit
unpacked Bayer formats, the sums are accumulated at native bit depth
while the AWB subtracts an 8-bit black level, under-correcting by 4x
or 16x respectively. This skews the AWB grey world gains, producing a
visible color cast (~9% green on the OV2740 with BLC=16). The fix
right-shifts the RGB sums in finishFrame() to normalize them to 8-bit
scale, matching the histogram and the 8-bit BLC used by AWB.

Patch 3 adds the OV2740 black level (4096, i.e. 0x40 at 10-bit) to
CameraSensorHelperOv2740, following the established pattern used by
OV5675, IMX219, and other sensors.

Changes since v3:
- Patch 1: Removed kExpMaxStep and the std::clamp - the proportional
  gain is applied directly, since the maximum error of ~2.5 already
  bounds the step to ~10%. (Barnabas)
- Patch 2: Replaced per-case sumShift_ assignments with
  sumShift_ = bayerFormat.bitDepth - 8. (Barnabas)
- Patch 3: No changes.

Changes since v2:
- Dropped the OV2740 tuning file patch (identical to uncalibrated.yaml
  without a CCM). A follow-up with calibrated CCMs is planned.
- Rebased onto current master.

Signed-off-by: Javier Tia <floss@jetm.me>
---
Javier Tia (3):
      ipa: simple: agc: Replace bang-bang controller with proportional
      libcamera: software_isp: Normalize statistics sums to 8-bit
      ipa: libipa: camera_sensor_helper: Add OV2740 black level

 .../libcamera/internal/software_isp/swstats_cpu.h  |  1 +
 src/ipa/libipa/camera_sensor_helper.cpp            |  2 +
 src/ipa/simple/algorithms/agc.cpp                  | 65 ++++++++++++++--------
 src/libcamera/software_isp/swstats_cpu.cpp         |  7 +++
 4 files changed, 51 insertions(+), 24 deletions(-)
---
base-commit: 14ba4d168085dd27aed9bcb043996d6a5f28867e
change-id: 20260305-agc-proportional-ba20bf95f40b

Best regards,

Comments

Martin Sofaru April 28, 2026, 8:36 p.m. UTC | #1 
Dear Javier,

On 3/6/26 19:46, floss at jetm.me (Javier Tia) wrote:
> This series fixes AGC oscillation and an AWB statistics bug in the
> Simple pipeline, and adds the OV2740 black level to the sensor helper.

thank you so much for this patchwork, which finally makes the ov7240 
camera in my thinkpad x1 yoga gen7 work. Without it i get heavy min/max 
flapping of the AGC.

I recompiled libcamera 0.7.0-2 in debian sid/forky with this patchset 
applied and it makes the camera usable.


Thank you pobrn for pointing me to this patchset.

Martin
Martin Sofaru April 28, 2026, 8:44 p.m. UTC | #2 
Apologies, I forgot to include the tag in my previous mail.

Tested-by: Martin Sofaru <libcamera@fhloston.org>