关于Touch Panel校准算法的研究.doc

关于Touch Panel校准算法的研究Haiyong Lei1. 概述由于存在机械误差和ADC误差, touch panel获取的点坐标与屏幕上的点坐标总是存在偏差, 所以touch panel需要通过一定的软件校准.2. 校准算法目前普遍采用的是5点校准, 即取屏幕四角各一个点加上中心一个点, 作为校准的基准参考, 如图1.图1: 校准点的位子五点的坐标定义为:左下: x0y0 (屏幕坐标), X0Y0 (TP坐标)左上: x0y1 (屏幕坐标), X0Y1 (TP坐标)右下: x1y0 (屏幕坐标), X1Y0 (TP坐标)右上: x1y1 (屏幕坐标), X1Y1 (TP坐标)中间: xcyc (屏幕坐标), XcYc (TP坐标)2.1 算法1算法1基于如下公式把TP坐标转换成屏幕坐标:x_screen = Kx * (X_tp - X_offset) / SCF + x_offsety_screen = Ky * (Y_tp - Y_offset) / SCF + y_offset其中Kx,y是X/Y轴比例因子：Kx = (x1 - x0) / (X1 - X0) * SCFKy = (y1 - y0) / (Y1 - Y0) * SCFX_offset用于消除偏离误差：x_offset = xcy_offset = ycX_offset = XcY_offset = YcSCF是SCALE FACTOR这里用于整数计算时保持计算精度。五个基准点包含的冗余信息, 可用于排除人为误差, 假定一个合理误差sigma，则以下公式近式成立:|X0 - X0| sigma, |X1 - X1| sigma|Y0 - Y0| sigma, |Y1 - Y1| sigma|Xc - (X1 + X0 + X1 + X0) / 4| sigma|Yc - (Y1 + Y0 + Y1 + Y0) / 4 | sigma校准完成后，Kx,y和X/Y_offset四个参数予以永久保存。算法1的优点是比较简单，缺点是无法消除TP屏倾斜误差。对于精度要求不高场合是个合适的选择。2.2 算法2算法2是tslib中采用的校准算法， tslib是开源TP算法库， 广泛使用在各种touch panel应用场合，特别是Android平台。tslib包含多种算法, 校准是其中之一, 具体公式如下:x_screen = (A0 * X_tp + A1 * Y_tp + A2) / A6y_screen = (A3 * X_tp + A4 * Y_tp + A5) / A6系数A0到A5经计算得出, A6是SCALE FACTOR.算法2的优点是效果最好，缺点是计算复杂，特别A0到A5的计算需要用到浮点，如果处理器不支持浮点运算的话，需要转换为定点运算。3 实现3.1 算法1/* * Copyright (C) 2015. * * Author: Haiyong Lei * */#ifndef TS_CALIB_H#define TS_CALIB_H/ DEBUG#define TS_DEBUG#ifdef TS_DEBUG#include #define TS_LOG printf#else#define TS_LOG#endif#define N_CALIB_POINTS5 / number points for calibration/ NAME OF POINTS#define LEFT_BOTTOM0#define LEFT_TOP1#define RIGHT_BOTTOM2#define RIGHT_TOP3#define CENTER4/ FLIP FLAGS#define FLIP_X1#define FLIP_Y2/ ERRORS#define E_SUCCESS0#define E_TOO_MANY_POINTS-1#define E_BAD_POINT_X0-2#define E_BAD_POINT_X1-3#define E_BAD_POINT_Y0-4#define E_BAD_POINT_Y1-5#define E_BAD_POINT_XCENTER-6#define E_BAD_POINT_YCENTER-7struct ts_calib_data int scr_xN_CALIB_POINTS;/ screen calibration pointsint scr_yN_CALIB_POINTS;int scr_xres;/ screen resolutionint scr_yres;int scr_xcenter;/ screen centerint scr_ycenter;int tp_xN_CALIB_POINTS;/ touch panel calibration pointsint tp_yN_CALIB_POINTS;int tp_xres;/ touch panel resolutionint tp_yres;int tp_xcenter;/ touch panel centerint tp_ycenter;int tp_xyflip;/ touch panel axis xy flip flagsint Kx;/ axis x ratioint Ky;/ axis y ratioint precision;/ calibration precisionint scaling;/ scaling factor;/* initialize touch panel calibration data: Params: scr_xres: screen x resolution scr_yres: screen i resolution tp_xres: tp x resolution tp_yres: tp y resolution Return:*/void ts_init(struct ts_calib_data *calib, int scr_xres, int scr_yres,int tp_xres, int tp_yres);/* set touch panel xy direction flip flags: Params: tp_xyflip: set the flag to flip Return:*/void ts_set_xyflip(struct ts_calib_data *calib, int tp_xyflip);/* reset touch panel xy direction flip flags: Params: tp_xyflip: set the flag to no flip Return:*/void ts_reset_xyflip(struct ts_calib_data *calib, int tp_xyflip);/* set calibration precision: Params: precision: the minimum in distance of two touch panel readingsthey can be considered the same. The unit is the touchpanel reading unit. Return:*/void ts_set_precision(struct ts_calib_data *calib, int precision);/* set calibration scaling: Params: scaling: the scaling factor, the default is 8192. Return:*/void ts_set_scaling(struct ts_calib_data *calib, int scaling);/* set calibration data: Params: Kx: the ratio of axis x. Ky: the ratio of axis y. tp_xcenter: touch panel center points axis x. tp_ycenter: touch panel center points axis y. Return:*/void ts_set_calib_data(struct ts_calib_data *calib, int Kx, int Ky,int tp_xcenter, int tp_ycenter);/* smooth N of touch panel continous readings: Params: x_in: N x reading of touch panel. y_in: N y reading of touch panel. n: the number of N. x_out: smoothed x reading output. y_out: smoothed y reading output. Return:*/void ts_smooth_xy(int *x_in, int *y_in, int n, int* x_out, int* y_out);/* convert touch panel coordinate to screen using the calibration data: Params: tp_x: x reading of touch panel. tp_y: y reading of touch panel. scr_x: screen x position output. scr_y: screen y position output. Return:*/void ts_linear_map_xy(struct ts_calib_data *calib, int tp_x, int tp_y, int *scr_x, int *scr_y);/* add calibration point Params: n: the Nth point used by calibration, N 5. scr_x: x position in screen coordinate. scr_y: y position in screen coordinate. tp_x: x reading of touch panel. tp_y: y reading of touch panel. Return: E_SUCCESS if succeed.*/int ts_add_calib_point(struct ts_calib_data *calib, int n, int scr_x, int scr_y, int tp_x, int tp_y);/* process calibration: Params: Return: E_SUCCESS if succeed. Note: use ts_add_calib_point to feed 5 points before calibration.*/int ts_calibrate(struct ts_calib_data *calib);#endif/* * Copyright (C) 2015. * * Author: Haiyong Lei * * The touchscreen calibration libray. * */#include #include ts_calib.h#define PRECISION40/ related to touch panel resolution, / example: if touch panel resolution is 4096,/ the precision is 40/4096.#define SCALING8192void ts_init(struct ts_calib_data *calib, int scr_xres, int scr_yres,int tp_xres, int tp_yres)TS_LOG(ts_calib init with resultion: screen: W%dx,H%d, tp: W%dx,H%d,scr_xres, scr_yres, tp_xres, tp_yres);memset(calib, 0, sizeof (struct ts_calib_data);calib-scr_xres = scr_xres;calib-scr_yres = scr_yres;calib-scr_xcenter = scr_xres / 2;calib-scr_ycenter = scr_yres / 2;calib-tp_xres = tp_xres;calib-tp_yres = tp_yres;calib-tp_xcenter = tp_xres / 2;calib-tp_ycenter = tp_yres / 2;calib-Kx = scr_xres * SCALING / tp_xres;calib-Ky = scr_yres * SCALING / tp_yres;calib-precision = PRECISION;calib-scaling = SCALING;void ts_set_xyflip(struct ts_calib_data *calib, int tp_xyflip)TS_LOG(ts_calib set xyflip: %d,tp_xyflip);calib-tp_xyflip |= tp_xyflip;void ts_reset_xyflip(struct ts_calib_data *calib, int tp_xyflip)TS_LOG(ts_calib reset xyflip: %d,tp_xyflip);calib-tp_xyflip &= tp_xyflip;void ts_set_precision(struct ts_calib_data *calib, int precision)TS_LOG(ts_calib set precision: %d,precision);calib-precision = precision;void ts_set_scaling(struct ts_calib_data *calib, int scaling)TS_LOG(ts_calib set scaling: %d,scaling);calib-scaling = scaling;void ts_set_calib_data(struct ts_calib_data *calib, int Kx, int Ky,int tp_xcenter, int tp_ycenter)TS_LOG(ts_calib set Kx/Ky: %d,%d, center: X%d,Y%d,Kx, Ky, tp_xcenter, tp_ycenter);calib-Kx = Kx;calib-Ky = Ky;calib-tp_xcenter = tp_xcenter;calib-tp_ycenter = tp_ycenter;/ smooth N points by averagingvoid ts_smooth_xy(int *x_in, int *y_in, int n, int* x_out, int* y_out)int x_sum = 0;int y_sum = 0;int i;/ average n samplesfor (i = 0; i tp_xyflip & FLIP_X)tp_x = calib-tp_xres - tp_x;if (calib-tp_xyflip & FLIP_Y)tp_y = calib-tp_yres - tp_y;if (*scr_x)int x = (calib-Kx * (tp_x - calib-tp_xcenter) / calib-scaling+ calib-scr_xcenter;/ boundary checkif (x calib-scr_xres)x = calib-scr_xres;*scr_x = x;if (*scr_y)int y = (calib-Ky * (tp_y - calib-tp_ycenter) / calib-scaling+ calib-scr_ycenter;/ boundary checkif (y calib-scr_yres)y = calib-scr_yres;*scr_y = y;int ts_add_calib_point(struct ts_calib_data *calib, int n, int scr_x, int scr_y, int tp_x, int tp_y)if (n = N_CALIB_POINTS)TS_LOG(ts_calib error: %dth point is out of range.,n);return E_TOO_MANY_POINTS;if (calib-tp_xyflip & FLIP_X)tp_x = calib-tp_xres - tp_x;if (calib-tp_xyflip & FLIP_Y)tp_y = calib-tp_yres - tp_y;calib-scr_xn = scr_x;calib-scr_yn = scr_y;calib-tp_xn = tp_x;calib-tp_yn = tp_y;TS_LOG(ts_calib add %dth point: screen: X%d,Y%d, tp: X%d,Y%d,n, scr_x, scr_y, tp_x, tp_y);return E_SUCCESS;/ variance(a0, a1, ., an) =/ 1/n * (a0 - a)2 + (a1 - a)2 + . (an - a)2,/ where, a = (a0 + a1 + . an) / n/static int variance(int p0, int p1)int pt = (p0 + p1) /2;int v = (p0 - pt) * (p0 - pt) +(p1 - pt) * (p1 - pt);return v /2;/* * the calibration procedure requires to collect five points: * * * (x0,y1 )-(x1,y1) * | | * | | * | | * | | * | | * | (x2,y2) | * | | * | | * | | * | | * | | * (x0 ,y0 )-(x1 ,y0) * * To linear convert touch panel coordinate to screen, we * use formula: * * x = Kx * (X - X2) / SCALING + x2 * y = Ky * (Y - Y2) / SCALING + x2 * * The ratio Kx,y can be computed by: * * Kx = (x1 - x0) / (X1 - X0) * SCALING * Ky = (y1 - y0) / (Y1 - Y0) * SCALING * * x, y: screen coordinates, X, Y: touch panel coordinates. * The SCALING factor is to keep calculation precision. * * The equation needs two points to solve, but we have five.The * redundant points can be used to valid points themselves, * points are considered enough good if: * * variance(X0, X0) precision2 * variance(X1, X1) precision2 * variance(Y0, Y0) precision2 * variance(Y1, Y1) precision2 * * and for the center point: * * X2 = (X1 + X0) + (X1 + X0) / 4 * Y2 = (Y1 + Y0) + (Y1 + Y0) / 4 * variance(X2, X2) precision2 * variance(Y2, Y2) precision * calib-precision;x00 = calib-tp_xLEFT_BOTTOM;x01 = calib-tp_xLEFT_TOP;x10 = calib-tp_xRIGHT_BOTTOM;x11 = calib-tp_xRIGHT_TOP;y00 = calib-tp_yLEFT_BOTTOM;y01 = calib-tp_yRIGHT_BOTTOM;y10 = calib-tp_yLEFT_TOP;y11 = calib-tp_yRIGHT_TOP;if (v = variance(x00, x01) square_prec)TS_LOG(ts_calib error: bad point x0: %d,%d, variance: %d%d.,x00, x01, v, square_prec);return E_BAD_POINT_X0;if (v = variance(x10, x11) square_prec)TS_LOG(ts_calib error: bad point x1: %d,%d, variance: %d%d.,x10, x11, v, square_prec);return E_BAD_POINT_X1;if (v = variance(y00, y01) square_prec)TS_LOG(ts_calib error: bad point y0: %d,%d, variance: %d%d.,y00, y01, v, square_prec);return E_BAD_POINT_Y0;if (v = variance(y10, x11) square_prec)TS_LOG(ts_calib error: bad point y1: %d,%d, variance: %d%d.,y10, y11, v, square_prec);return E_BAD_POINT_Y1;x20 = calib-tp_xCENTER;y20 = calib-tp_yCENTER;x21 = (x10 + x11 + x00 + x01) / 4;y21 = (y10 + y11 + y00 + y01) / 4;if (v = variance(x20, x21) square_prec)TS_LOG(ts_calib error: bad point x2: %d,%d, variance: %d%d.,x20, x21, v, square_prec);return E_BAD_POINT_XCENTER;if (v = variance(y20, y21) square_prec)TS_LOG(ts_calib error: bad point y2: %d,%d, variance: %d%d.,y20, y21, v, square_prec);return E_BAD_POINT_YCENTER;scr_xdist = calib-scr_xRIGHT_BOTTOM - calib-scr_xLEFT_BOTTOM;scr_ydist = calib-scr_yLEFT_TOP - calib-scr_yLEFT_BOTTO