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authorDavid Plowman <david.plowman@raspberrypi.com>2020-11-23 07:37:58 +0000
committerKieran Bingham <kieran.bingham@ideasonboard.com>2020-11-23 14:24:24 +0000
commit9db94a3635b8cc0963fdbc8e33c07890ce177359 (patch)
tree11743b34587a39b1fb288600e3e3c6e2e750f617 /src/ipa
parent6af665992d48eb30bda901af73294f83b17876e7 (diff)
libcamera: ipa: raspberrypi: agc: Improve centre-weighted luminance calucation
Previously the calculation computed Y for each region before returning the weighted average, which "baked in" the over-importance of small statistics regions. The revised calculation will treat all pixels equally when the region weights are the same, making it easier to use. With the previous scheme, proper "average" metering was difficult to implement. Signed-off-by: David Plowman <david.plowman@raspberrypi.com> Reviewed-by: Naushir Patuck <naush@raspberrypi.com> Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Diffstat (limited to 'src/ipa')
-rw-r--r--src/ipa/raspberrypi/controller/rpi/agc.cpp25
1 files changed, 15 insertions, 10 deletions
diff --git a/src/ipa/raspberrypi/controller/rpi/agc.cpp b/src/ipa/raspberrypi/controller/rpi/agc.cpp
index 9a5d84f7..f0c70a0a 100644
--- a/src/ipa/raspberrypi/controller/rpi/agc.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/agc.cpp
@@ -385,18 +385,23 @@ static double compute_initial_Y(bcm2835_isp_stats *stats, Metadata *image_metada
awb.gain_r = awb.gain_g = awb.gain_b = 1.0; // in case no metadata
if (image_metadata->Get("awb.status", awb) != 0)
LOG(RPiAgc, Warning) << "Agc: no AWB status found";
- double Y_sum = 0, weight_sum = 0;
+ // Note how the calculation below means that equal weights give you
+ // "average" metering (i.e. all pixels equally important).
+ double R_sum = 0, G_sum = 0, B_sum = 0, pixel_sum = 0;
for (int i = 0; i < AGC_STATS_SIZE; i++) {
- if (regions[i].counted == 0)
- continue;
- weight_sum += weights[i];
- double Y = regions[i].r_sum * awb.gain_r * .299 +
- regions[i].g_sum * awb.gain_g * .587 +
- regions[i].b_sum * awb.gain_b * .114;
- Y /= regions[i].counted;
- Y_sum += Y * weights[i];
+ R_sum += regions[i].r_sum * weights[i];
+ G_sum += regions[i].g_sum * weights[i];
+ B_sum += regions[i].b_sum * weights[i];
+ pixel_sum += regions[i].counted * weights[i];
}
- return Y_sum / weight_sum / (1 << PIPELINE_BITS);
+ if (pixel_sum == 0.0) {
+ LOG(RPiAgc, Warning) << "compute_initial_Y: pixel_sum is zero";
+ return 0;
+ }
+ double Y_sum = R_sum * awb.gain_r * .299 +
+ G_sum * awb.gain_g * .587 +
+ B_sum * awb.gain_b * .114;
+ return Y_sum / pixel_sum / (1 << PIPELINE_BITS);
}
// We handle extra gain through EV by adjusting our Y targets. However, you