linux/drivers/media/usb/gspca/autogain_functions.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Functions for auto gain.
 *
 * Copyright (C) 2010-2012 Hans de Goede <hdegoede@redhat.com>
 */
#include "gspca.h"

/* auto gain and exposure algorithm based on the knee algorithm described here:
   http://ytse.tricolour.net/docs/LowLightOptimization.html

   Returns 0 if no changes were made, 1 if the gain and or exposure settings
   where changed. */
int gspca_expo_autogain(
			struct gspca_dev *gspca_dev,
			int avg_lum,
			int desired_avg_lum,
			int deadzone,
			int gain_knee,
			int exposure_knee)
{
	s32 gain, orig_gain, exposure, orig_exposure;
	int i, steps, retval = 0;

	if (v4l2_ctrl_g_ctrl(gspca_dev->autogain) == 0)
		return 0;

	orig_gain = gain = v4l2_ctrl_g_ctrl(gspca_dev->gain);
	orig_exposure = exposure = v4l2_ctrl_g_ctrl(gspca_dev->exposure);

	/* If we are of a multiple of deadzone, do multiple steps to reach the
	   desired lumination fast (with the risc of a slight overshoot) */
	steps = abs(desired_avg_lum - avg_lum) / deadzone;

	gspca_dbg(gspca_dev, D_FRAM, "autogain: lum: %d, desired: %d, steps: %d\n",
		  avg_lum, desired_avg_lum, steps);

	for (i = 0; i < steps; i++) {
		if (avg_lum > desired_avg_lum) {
			if (gain > gain_knee)
				gain--;
			else if (exposure > exposure_knee)
				exposure--;
			else if (gain > gspca_dev->gain->default_value)
				gain--;
			else if (exposure > gspca_dev->exposure->minimum)
				exposure--;
			else if (gain > gspca_dev->gain->minimum)
				gain--;
			else
				break;
		} else {
			if (gain < gspca_dev->gain->default_value)
				gain++;
			else if (exposure < exposure_knee)
				exposure++;
			else if (gain < gain_knee)
				gain++;
			else if (exposure < gspca_dev->exposure->maximum)
				exposure++;
			else if (gain < gspca_dev->gain->maximum)
				gain++;
			else
				break;
		}
	}

	if (gain != orig_gain) {
		v4l2_ctrl_s_ctrl(gspca_dev->gain, gain);
		retval = 1;
	}
	if (exposure != orig_exposure) {
		v4l2_ctrl_s_ctrl(gspca_dev->exposure, exposure);
		retval = 1;
	}

	if (retval)
		gspca_dbg(gspca_dev, D_FRAM, "autogain: changed gain: %d, expo: %d\n",
			  gain, exposure);
	return retval;
}
EXPORT_SYMBOL(gspca_expo_autogain);

/* Autogain + exposure algorithm for cameras with a coarse exposure control
   (usually this means we can only control the clockdiv to change exposure)
   As changing the clockdiv so that the fps drops from 30 to 15 fps for
   example, will lead to a huge exposure change (it effectively doubles),
   this algorithm normally tries to only adjust the gain (between 40 and
   80 %) and if that does not help, only then changes exposure. This leads
   to a much more stable image then using the knee algorithm which at
   certain points of the knee graph will only try to adjust exposure,
   which leads to oscillating as one exposure step is huge.

   Returns 0 if no changes were made, 1 if the gain and or exposure settings
   where changed. */
int gspca_coarse_grained_expo_autogain(
			struct gspca_dev *gspca_dev,
			int avg_lum,
			int desired_avg_lum,
			int deadzone)
{
	s32 gain_low, gain_high, gain, orig_gain, exposure, orig_exposure;
	int steps, retval = 0;

	if (v4l2_ctrl_g_ctrl(gspca_dev->autogain) == 0)
		return 0;

	orig_gain = gain = v4l2_ctrl_g_ctrl(gspca_dev->gain);
	orig_exposure = exposure = v4l2_ctrl_g_ctrl(gspca_dev->exposure);

	gain_low  = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
		    5 * 2 + gspca_dev->gain->minimum;
	gain_high = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
		    5 * 4 + gspca_dev->gain->minimum;

	/* If we are of a multiple of deadzone, do multiple steps to reach the
	   desired lumination fast (with the risc of a slight overshoot) */
	steps = (desired_avg_lum - avg_lum) / deadzone;

	gspca_dbg(gspca_dev, D_FRAM, "autogain: lum: %d, desired: %d, steps: %d\n",
		  avg_lum, desired_avg_lum, steps);

	if ((gain + steps) > gain_high &&
	    exposure < gspca_dev->exposure->maximum) {
		gain = gain_high;
		gspca_dev->exp_too_low_cnt++;
		gspca_dev->exp_too_high_cnt = 0;
	} else if ((gain + steps) < gain_low &&
		   exposure > gspca_dev->exposure->minimum) {
		gain = gain_low;
		gspca_dev->exp_too_high_cnt++;
		gspca_dev->exp_too_low_cnt = 0;
	} else {
		gain += steps;
		if (gain > gspca_dev->gain->maximum)
			gain = gspca_dev->gain->maximum;
		else if (gain < gspca_dev->gain->minimum)
			gain = gspca_dev->gain->minimum;
		gspca_dev->exp_too_high_cnt = 0;
		gspca_dev->exp_too_low_cnt = 0;
	}

	if (gspca_dev->exp_too_high_cnt > 3) {
		exposure--;
		gspca_dev->exp_too_high_cnt = 0;
	} else if (gspca_dev->exp_too_low_cnt > 3) {
		exposure++;
		gspca_dev->exp_too_low_cnt = 0;
	}

	if (gain != orig_gain) {
		v4l2_ctrl_s_ctrl(gspca_dev->gain, gain);
		retval = 1;
	}
	if (exposure != orig_exposure) {
		v4l2_ctrl_s_ctrl(gspca_dev->exposure, exposure);
		retval = 1;
	}

	if (retval)
		gspca_dbg(gspca_dev, D_FRAM, "autogain: changed gain: %d, expo: %d\n",
			  gain, exposure);
	return retval;
}
EXPORT_SYMBOL(gspca_coarse_grained_expo_autogain);