[PATCH 05/18] media: microchip-isc: Use channel averages for Grey World AWB

Balamanikandan Gunasundar
2025-10-09T15:54:08Z

From: Balakrishnan Sambath <balakrishnan.s@microchip.com>

Replace pixel counting with actual pixel intensity averages in Grey
World algorithm for more accurate white balance calculation.This
provides better color correction especially in mixed lighting
conditions.

Signed-off-by: Balakrishnan Sambath <balakrishnan.s@microchip.com>
---
.../platform/microchip/microchip-isc-base.c | 35 ++++++++++---------
1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/drivers/media/platform/microchip/microchip-isc-base.c b/drivers/media/platform/microchip/microchip-isc-base.c
index 956bdea830e3..bb2dd69a83f0 100644
--- a/drivers/media/platform/microchip/microchip-isc-base.c
+++ b/drivers/media/platform/microchip/microchip-isc-base.c
@@ -1317,7 +1317,6 @@ static void isc_hist_count(struct isc_device *isc, u32 *min, u32 *max)
static void isc_wb_update(struct isc_ctrls *ctrls)
{
struct isc_device *isc = container_of(ctrls, struct isc_device, ctrls);
- u32 *hist_count = &ctrls->hist_count[0];
u32 c, offset[4];
u64 avg = 0;
/* We compute two gains, stretch gain and grey world gain */
@@ -1328,10 +1327,10 @@ static void isc_wb_update(struct isc_ctrls *ctrls)
* them towards the green channel.
* Thus we want to keep Green as fixed and adjust only Red/Blue
* Compute the average of the both green channels first
+ * Use channel averages for Grey World algorithm
*/
- avg = (u64)hist_count[ISC_HIS_CFG_MODE_GR] +
- (u64)hist_count[ISC_HIS_CFG_MODE_GB];
- avg >>= 1;
+ avg = (ctrls->channel_avg[ISC_HIS_CFG_MODE_GR] +
+ ctrls->channel_avg[ISC_HIS_CFG_MODE_GB]) >> 1;

dev_dbg(isc->dev, "isc wb: green components average %llu\n", avg);

@@ -1340,6 +1339,11 @@ static void isc_wb_update(struct isc_ctrls *ctrls)
return;

for (c = ISC_HIS_CFG_MODE_GR; c <= ISC_HIS_CFG_MODE_B; c++) {
+ u32 hist_min = ctrls->hist_minmax[c][HIST_MIN_INDEX];
+ u32 hist_max = ctrls->hist_minmax[c][HIST_MAX_INDEX];
+ u32 channel_avg = ctrls->channel_avg[c];
+ u32 total_pixels = ctrls->total_pixels[c];
+
/*
* the color offset is the minimum value of the histogram.
* we stretch this color to the full range by substracting
@@ -1373,23 +1377,21 @@ static void isc_wb_update(struct isc_ctrls *ctrls)
* decimals
*/
s_gain[c] = (HIST_ENTRIES << 9) /
- (ctrls->hist_minmax[c][HIST_MAX_INDEX] -
- ctrls->hist_minmax[c][HIST_MIN_INDEX] + 1);
+ (hist_max - hist_min + 1);

/*
- * Now we have to compute the gain w.r.t. the average.
- * Add/lose gain to the component towards the average.
- * If it happens that the component is zero, use the
- * fixed point value : 1.0 gain.
+ * Grey World gain using channel averages
+ * This is much more accurate than using hist_count
*/
- if (hist_count[c])
- gw_gain[c] = div_u64(avg << 9, hist_count[c]);
+ if (channel_avg > 0 && total_pixels > 1000)
+ gw_gain[c] = div64_u64((avg << 9), channel_avg);
else
gw_gain[c] = 1 << 9;

dev_dbg(isc->dev,
- "isc wb: component %d, s_gain %u, gw_gain %u\n",
- c, s_gain[c], gw_gain[c]);
+ "isc wb: component %d, black_level=%u, avg=%u, s_gain=%u, gw_gain=%u",
+ c, hist_min, channel_avg, s_gain[c], gw_gain[c]);
+
/* multiply both gains and adjust for decimals */
ctrls->gain[c] = s_gain[c] * gw_gain[c];
ctrls->gain[c] >>= 9;
@@ -1397,8 +1399,9 @@ static void isc_wb_update(struct isc_ctrls *ctrls)
/* make sure we are not out of range */
ctrls->gain[c] = clamp_val(ctrls->gain[c], 0, GENMASK(12, 0));

- dev_dbg(isc->dev, "isc wb: component %d, final gain %u\n",
- c, ctrls->gain[c]);
+ dev_dbg(isc->dev,
+ "isc wb: component %d, final gain %u, offset %d\n",
+ c, ctrls->gain[c], ctrls->offset[c]);
}
}

--
2.34.1