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autogain.c

/*
#             (C) 2008-2009 Hans de Goede <hdegoede@redhat.com>

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include "libv4lprocessing.h"
#include "libv4lprocessing-priv.h"
#include "../libv4lconvert-priv.h" /* for PIX_FMT defines */
#include "../libv4lsyscall-priv.h"

static int autogain_active(struct v4lprocessing_data *data) {
  int autogain;

  autogain = v4lcontrol_get_ctrl(data->control, V4LCONTROL_AUTOGAIN);
  if (!autogain) {
    /* Reset last_correction val */
    data->last_gain_correction = 0;
  }

  return autogain;
}

/* auto gain and exposure algorithm based on the knee algorithm described here:
   http://ytse.tricolour.net/docs/LowLightOptimization.html */
static int autogain_calculate_lookup_tables(
  struct v4lprocessing_data *data,
  unsigned char *buf, const struct v4l2_format *fmt)
{
  int x, y, target, steps, avg_lum = 0;
  int gain, exposure, orig_gain, orig_exposure, exposure_low;
  struct v4l2_control ctrl;
  struct v4l2_queryctrl gainctrl, expoctrl;
  const int deadzone = 6;

  ctrl.id = V4L2_CID_EXPOSURE;
  expoctrl.id = V4L2_CID_EXPOSURE;
  if (SYS_IOCTL(data->fd, VIDIOC_QUERYCTRL, &expoctrl) ||
      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;
  exposure_low += expoctrl.minimum;

  ctrl.id = V4L2_CID_GAIN;
  gainctrl.id = V4L2_CID_GAIN;
  if (SYS_IOCTL(data->fd, VIDIOC_QUERYCTRL, &gainctrl) ||
      SYS_IOCTL(data->fd, VIDIOC_G_CTRL, &ctrl))
    return 0;
  gain = orig_gain = ctrl.value;

  switch (fmt->fmt.pix.pixelformat) {
    case V4L2_PIX_FMT_SGBRG8:
    case V4L2_PIX_FMT_SGRBG8:
    case V4L2_PIX_FMT_SBGGR8:
    case V4L2_PIX_FMT_SRGGB8:
      buf += fmt->fmt.pix.height * fmt->fmt.pix.bytesperline / 4 +
           fmt->fmt.pix.width / 4;

      for (y = 0; y < fmt->fmt.pix.height / 2; y++) {
      for (x = 0; x < fmt->fmt.pix.width / 2; x++) {
        avg_lum += *buf++;
      }
      buf += fmt->fmt.pix.bytesperline - fmt->fmt.pix.width / 2;
      }
      avg_lum /= fmt->fmt.pix.height * fmt->fmt.pix.width / 4;
      break;

    case V4L2_PIX_FMT_RGB24:
    case V4L2_PIX_FMT_BGR24:
      buf += fmt->fmt.pix.height * fmt->fmt.pix.bytesperline / 4 +
           fmt->fmt.pix.width * 3 / 4;

      for (y = 0; y < fmt->fmt.pix.height / 2; y++) {
      for (x = 0; x < fmt->fmt.pix.width / 2; x++) {
        avg_lum += *buf++;
        avg_lum += *buf++;
        avg_lum += *buf++;
      }
      buf += fmt->fmt.pix.bytesperline - fmt->fmt.pix.width * 3 / 2;
      }
      avg_lum /= fmt->fmt.pix.height * fmt->fmt.pix.width * 3 / 4;
      break;
  }

  /* If we are off a multiple of deadzone, do multiple steps to reach the
     desired lumination fast (with the risc of a slight overshoot) */
  target = v4lcontrol_get_ctrl(data->control, V4LCONTROL_AUTOGAIN_TARGET);
  steps = (target - avg_lum) / deadzone;

  /* If we were decreasing and are now increasing, or vica versa, half the
     number of steps to avoid overshooting and oscilating */
  if ((steps > 0 && data->last_gain_correction < 0) ||
      (steps < 0 && data->last_gain_correction > 0))
    steps /= 2;

  for (x = 0; x < abs(steps); x++) {
    if (avg_lum > target) {
      if (exposure > expoctrl.default_value)
      exposure--;
      else if (gain > gainctrl.default_value)
      gain--;
      else if (exposure > exposure_low)
      exposure--;
      else if (gain > gainctrl.minimum)
      gain--;
      else if (exposure > expoctrl.minimum)
      exposure--;
      else
      break;
    } else {
      if (exposure < exposure_low)
      exposure++;
      else if (gain < gainctrl.default_value)
      gain++;
      else if (exposure < expoctrl.default_value)
      exposure++;
      else if (gain < gainctrl.maximum)
      gain++;
      else if (exposure < expoctrl.maximum)
      exposure++;
      else
      break;
    }
  }

  if (steps)
    data->last_gain_correction = steps;

  if (gain != orig_gain) {
    ctrl.id = V4L2_CID_GAIN;
    ctrl.value = gain;
    SYS_IOCTL(data->fd, VIDIOC_S_CTRL, &ctrl);
  }
  if (exposure != orig_exposure) {
    ctrl.id = V4L2_CID_EXPOSURE;
    ctrl.value = exposure;
    SYS_IOCTL(data->fd, VIDIOC_S_CTRL, &ctrl);
  }

  return 0;
}

struct v4lprocessing_filter autogain_filter = {
  autogain_active, autogain_calculate_lookup_tables };

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