libv4l: autogain: avoid very low exposure values

Determine a value below which we try to not lower the exposure,
as most exposure controls tend to jump with big steps in the low
range, causing oscilation, so we prefer to use gain when exposure
has hit this value.

Priority: normal

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

diff --git a/lib/libv4lconvert/processing/autogain.c b/lib/libv4lconvert/processing/autogain.c
index 1d1e279..375d411 100644 (file)
--- a/lib/libv4lconvert/processing/autogain.c
+++ b/lib/libv4lconvert/processing/autogain.c
@@ -46,7 +46,7 @@ static int autogain_calculate_lookup_tables(
   unsigned char *buf, const struct v4l2_format *fmt)
 {
   int x, y, target, steps, avg_lum = 0;
-  int gain, exposure, orig_gain, orig_exposure;
+  int gain, exposure, orig_gain, orig_exposure, exposure_low;
   struct v4l2_control ctrl;
   struct v4l2_queryctrl gainctrl, expoctrl;
   const int deadzone = 6;
@@ -57,6 +57,14 @@ static int autogain_calculate_lookup_tables(
       SYS_IOCTL(data->fd, VIDIOC_G_CTRL, &ctrl))
     return 0;
   exposure = orig_exposure = ctrl.value;
+  /* Determine a value below which we try to not lower the exposure,
+     as most exposure controls tend to jump with big steps in the low
+     range, causing oscilation, so we prefer to use gain when exposure
+     has hit this value */
+  exposure_low = expoctrl.maximum / 10;
+  /* If we have a fine grained exposure control only avoid the last 10 steps */
+  if (exposure_low > 10)
+    exposure_low = 10;
 
   ctrl.id = V4L2_CID_GAIN;
   gainctrl.id = V4L2_CID_GAIN;
@@ -116,14 +124,18 @@ static int autogain_calculate_lookup_tables(
        exposure--;
       else if (gain > gainctrl.default_value)
        gain--;
-      else if (exposure > expoctrl.minimum)
+      else if (exposure > exposure_low)
        exposure--;
       else if (gain > gainctrl.minimum)
        gain--;
+      else if (exposure > expoctrl.minimum)
+       exposure--;
       else
        break;
     } else {
-      if (gain < gainctrl.default_value)
+      if (exposure < exposure_low)
+       exposure++;
+      else if (gain < gainctrl.default_value)
        gain++;
       else if (exposure < expoctrl.default_value)
        exposure++;