1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Functions for auto gain.
4  *
5  * Copyright (C) 2010-2012 Hans de Goede <hdegoede@redhat.com>
6  */
7 #include "gspca.h"
8 
9 /* auto gain and exposure algorithm based on the knee algorithm described here:
10    http://ytse.tricolour.net/docs/LowLightOptimization.html
11 
12    Returns 0 if no changes were made, 1 if the gain and or exposure settings
13    where changed. */
14 int gspca_expo_autogain(
15 			struct gspca_dev *gspca_dev,
16 			int avg_lum,
17 			int desired_avg_lum,
18 			int deadzone,
19 			int gain_knee,
20 			int exposure_knee)
21 {
22 	s32 gain, orig_gain, exposure, orig_exposure;
23 	int i, steps, retval = 0;
24 
25 	if (v4l2_ctrl_g_ctrl(gspca_dev->autogain) == 0)
26 		return 0;
27 
28 	orig_gain = gain = v4l2_ctrl_g_ctrl(gspca_dev->gain);
29 	orig_exposure = exposure = v4l2_ctrl_g_ctrl(gspca_dev->exposure);
30 
31 	/* If we are of a multiple of deadzone, do multiple steps to reach the
32 	   desired lumination fast (with the risc of a slight overshoot) */
33 	steps = abs(desired_avg_lum - avg_lum) / deadzone;
34 
35 	gspca_dbg(gspca_dev, D_FRAM, "autogain: lum: %d, desired: %d, steps: %d\n",
36 		  avg_lum, desired_avg_lum, steps);
37 
38 	for (i = 0; i < steps; i++) {
39 		if (avg_lum > desired_avg_lum) {
40 			if (gain > gain_knee)
41 				gain--;
42 			else if (exposure > exposure_knee)
43 				exposure--;
44 			else if (gain > gspca_dev->gain->default_value)
45 				gain--;
46 			else if (exposure > gspca_dev->exposure->minimum)
47 				exposure--;
48 			else if (gain > gspca_dev->gain->minimum)
49 				gain--;
50 			else
51 				break;
52 		} else {
53 			if (gain < gspca_dev->gain->default_value)
54 				gain++;
55 			else if (exposure < exposure_knee)
56 				exposure++;
57 			else if (gain < gain_knee)
58 				gain++;
59 			else if (exposure < gspca_dev->exposure->maximum)
60 				exposure++;
61 			else if (gain < gspca_dev->gain->maximum)
62 				gain++;
63 			else
64 				break;
65 		}
66 	}
67 
68 	if (gain != orig_gain) {
69 		v4l2_ctrl_s_ctrl(gspca_dev->gain, gain);
70 		retval = 1;
71 	}
72 	if (exposure != orig_exposure) {
73 		v4l2_ctrl_s_ctrl(gspca_dev->exposure, exposure);
74 		retval = 1;
75 	}
76 
77 	if (retval)
78 		gspca_dbg(gspca_dev, D_FRAM, "autogain: changed gain: %d, expo: %d\n",
79 			  gain, exposure);
80 	return retval;
81 }
82 EXPORT_SYMBOL(gspca_expo_autogain);
83 
84 /* Autogain + exposure algorithm for cameras with a coarse exposure control
85    (usually this means we can only control the clockdiv to change exposure)
86    As changing the clockdiv so that the fps drops from 30 to 15 fps for
87    example, will lead to a huge exposure change (it effectively doubles),
88    this algorithm normally tries to only adjust the gain (between 40 and
89    80 %) and if that does not help, only then changes exposure. This leads
90    to a much more stable image then using the knee algorithm which at
91    certain points of the knee graph will only try to adjust exposure,
92    which leads to oscillating as one exposure step is huge.
93 
94    Returns 0 if no changes were made, 1 if the gain and or exposure settings
95    where changed. */
96 int gspca_coarse_grained_expo_autogain(
97 			struct gspca_dev *gspca_dev,
98 			int avg_lum,
99 			int desired_avg_lum,
100 			int deadzone)
101 {
102 	s32 gain_low, gain_high, gain, orig_gain, exposure, orig_exposure;
103 	int steps, retval = 0;
104 
105 	if (v4l2_ctrl_g_ctrl(gspca_dev->autogain) == 0)
106 		return 0;
107 
108 	orig_gain = gain = v4l2_ctrl_g_ctrl(gspca_dev->gain);
109 	orig_exposure = exposure = v4l2_ctrl_g_ctrl(gspca_dev->exposure);
110 
111 	gain_low  = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
112 		    5 * 2 + gspca_dev->gain->minimum;
113 	gain_high = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
114 		    5 * 4 + gspca_dev->gain->minimum;
115 
116 	/* If we are of a multiple of deadzone, do multiple steps to reach the
117 	   desired lumination fast (with the risc of a slight overshoot) */
118 	steps = (desired_avg_lum - avg_lum) / deadzone;
119 
120 	gspca_dbg(gspca_dev, D_FRAM, "autogain: lum: %d, desired: %d, steps: %d\n",
121 		  avg_lum, desired_avg_lum, steps);
122 
123 	if ((gain + steps) > gain_high &&
124 	    exposure < gspca_dev->exposure->maximum) {
125 		gain = gain_high;
126 		gspca_dev->exp_too_low_cnt++;
127 		gspca_dev->exp_too_high_cnt = 0;
128 	} else if ((gain + steps) < gain_low &&
129 		   exposure > gspca_dev->exposure->minimum) {
130 		gain = gain_low;
131 		gspca_dev->exp_too_high_cnt++;
132 		gspca_dev->exp_too_low_cnt = 0;
133 	} else {
134 		gain += steps;
135 		if (gain > gspca_dev->gain->maximum)
136 			gain = gspca_dev->gain->maximum;
137 		else if (gain < gspca_dev->gain->minimum)
138 			gain = gspca_dev->gain->minimum;
139 		gspca_dev->exp_too_high_cnt = 0;
140 		gspca_dev->exp_too_low_cnt = 0;
141 	}
142 
143 	if (gspca_dev->exp_too_high_cnt > 3) {
144 		exposure--;
145 		gspca_dev->exp_too_high_cnt = 0;
146 	} else if (gspca_dev->exp_too_low_cnt > 3) {
147 		exposure++;
148 		gspca_dev->exp_too_low_cnt = 0;
149 	}
150 
151 	if (gain != orig_gain) {
152 		v4l2_ctrl_s_ctrl(gspca_dev->gain, gain);
153 		retval = 1;
154 	}
155 	if (exposure != orig_exposure) {
156 		v4l2_ctrl_s_ctrl(gspca_dev->exposure, exposure);
157 		retval = 1;
158 	}
159 
160 	if (retval)
161 		gspca_dbg(gspca_dev, D_FRAM, "autogain: changed gain: %d, expo: %d\n",
162 			  gain, exposure);
163 	return retval;
164 }
165 EXPORT_SYMBOL(gspca_coarse_grained_expo_autogain);
166