117 lines
4.0 KiB
C
117 lines
4.0 KiB
C
/*
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* Auto gain algorithm for camera's with a coarse exposure control
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*
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* Copyright (C) 2010 Hans de Goede <hdegoede@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/* Autogain + exposure algorithm for cameras with a coarse exposure control
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(usually this means we can only control the clockdiv to change exposure)
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As changing the clockdiv so that the fps drops from 30 to 15 fps for
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example, will lead to a huge exposure change (it effectively doubles),
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this algorithm normally tries to only adjust the gain (between 40 and
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80 %) and if that does not help, only then changes exposure. This leads
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to a much more stable image then using the knee algorithm which at
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certain points of the knee graph will only try to adjust exposure,
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which leads to oscilating as one exposure step is huge.
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Note this assumes that the sd struct for the cam in question has
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exp_too_high_cnt and exp_too_high_cnt int members for use by this function.
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Returns 0 if no changes were made, 1 if the gain and or exposure settings
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where changed. */
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static int gspca_coarse_grained_expo_autogain(struct gspca_dev *gspca_dev,
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int avg_lum, int desired_avg_lum, int deadzone)
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{
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int i, steps, gain, orig_gain, exposure, orig_exposure;
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int gain_low, gain_high;
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const struct ctrl *gain_ctrl = NULL;
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const struct ctrl *exposure_ctrl = NULL;
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struct sd *sd = (struct sd *) gspca_dev;
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int retval = 0;
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for (i = 0; i < gspca_dev->sd_desc->nctrls; i++) {
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if (gspca_dev->ctrl_dis & (1 << i))
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continue;
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if (gspca_dev->sd_desc->ctrls[i].qctrl.id == V4L2_CID_GAIN)
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gain_ctrl = &gspca_dev->sd_desc->ctrls[i];
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if (gspca_dev->sd_desc->ctrls[i].qctrl.id == V4L2_CID_EXPOSURE)
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exposure_ctrl = &gspca_dev->sd_desc->ctrls[i];
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}
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if (!gain_ctrl || !exposure_ctrl) {
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PDEBUG(D_ERR, "Error: gspca_coarse_grained_expo_autogain "
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"called on cam without gain or exposure");
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return 0;
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}
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if (gain_ctrl->get(gspca_dev, &gain) ||
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exposure_ctrl->get(gspca_dev, &exposure))
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return 0;
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orig_gain = gain;
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orig_exposure = exposure;
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gain_low =
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(gain_ctrl->qctrl.maximum - gain_ctrl->qctrl.minimum) / 5 * 2;
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gain_low += gain_ctrl->qctrl.minimum;
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gain_high =
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(gain_ctrl->qctrl.maximum - gain_ctrl->qctrl.minimum) / 5 * 4;
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gain_high += gain_ctrl->qctrl.minimum;
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/* If we are of a multiple of deadzone, do multiple steps to reach the
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desired lumination fast (with the risc of a slight overshoot) */
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steps = (desired_avg_lum - avg_lum) / deadzone;
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PDEBUG(D_FRAM, "autogain: lum: %d, desired: %d, steps: %d",
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avg_lum, desired_avg_lum, steps);
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if ((gain + steps) > gain_high &&
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sd->exposure < exposure_ctrl->qctrl.maximum) {
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gain = gain_high;
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sd->exp_too_low_cnt++;
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} else if ((gain + steps) < gain_low &&
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sd->exposure > exposure_ctrl->qctrl.minimum) {
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gain = gain_low;
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sd->exp_too_high_cnt++;
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} else {
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gain += steps;
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if (gain > gain_ctrl->qctrl.maximum)
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gain = gain_ctrl->qctrl.maximum;
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else if (gain < gain_ctrl->qctrl.minimum)
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gain = gain_ctrl->qctrl.minimum;
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sd->exp_too_high_cnt = 0;
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sd->exp_too_low_cnt = 0;
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}
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if (sd->exp_too_high_cnt > 3) {
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exposure--;
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sd->exp_too_high_cnt = 0;
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} else if (sd->exp_too_low_cnt > 3) {
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exposure++;
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sd->exp_too_low_cnt = 0;
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}
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if (gain != orig_gain) {
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gain_ctrl->set(gspca_dev, gain);
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retval = 1;
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}
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if (exposure != orig_exposure) {
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exposure_ctrl->set(gspca_dev, exposure);
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retval = 1;
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}
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return retval;
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}
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