Mitre_sfr代码注解（二） sfrproc函数
笔者学识有限。 本博客旨在对mitre_sfr核心代码进行简单注解， 详细内容读者仁者见仁智者见智。
bsfrproc函数是ISO12233附录A代码中的同名函数， 也是mitre_sfr中最核心的函数。因此对sfrproc函数的理解至关重要， 如果读者想对mitre_sfr功能进行自定义的移植， 最重要的就是对这个函数的移植与理解。
sfrproc函数涵盖了ISO12233 Sect 6.3.2 中绝大部分的内容， 整个SFR计算的核心内容都在这个函数里面， 包含了下列步骤的主干(具体函数的注解见后续博文， 本文以核心函数注解为主， 其他main函数涉及的其他非主要部分函数， 且有必要注解的函数见后续再另行注解)：
1. 寻找sfr刀口的质心（locate_centroids函数）
2. 拟合刀口划过的直线（fit函数）
3. 刀口的超采样（ESF）（bin_to_regular_xgrid函数）
4. ESF转换为LSF（calculate_derivative函数）
5. 对LSF加汉明窗（apply_hamming_window函数）
6. 计算SFR（ftwos函数）
short sfrProc (double **freq, double **sfr,
int *len,
double *farea,
unsigned short size_x, int *nrows,
double *slope, int *numcycles, int *pcnt2, double *off, double *R2,
int version, int iterate, int user_angle)
{
unsigned short i, j, col, err = 0;
long pcnt;
double dt, dt1, sfrc, tmp, tmp2;
double *temp=NULL, *shifts=NULL, *edgex=NULL, *Signal=NULL;
double *AveEdge=NULL, *AveTmp=NULL;
long *counts=NULL;
int nzero;
unsigned short size_y;
unsigned int bin_len;
double avar, bvar, offset1, offset2, offset;
double centroid;
int start_row, center_row;
double *farea_old;
double cyclelimit;
FILE *fp = NULL;
size_y = *nrows;
/* Verify input selection dimensions are EVEN */
if (size_x%2 != 0) {
fprintf(stderr, "ROI width is not even. Does this really matter???\n");
return 1;
}
/* At least this many cycles required. */
/* For special iterative versions of the code, it can go lower */
if (iterate) cyclelimit = 1.0;
else cyclelimit = 5.0;
/* Allocate memory */
shifts = (double *)malloc(size_y*sizeof(double));
temp = (double *)malloc(size_y*sizeof(double));
edgex = (double *)malloc(size_y*size_x*sizeof(double));
Signal = (double *)malloc(size_y*size_x*sizeof(double));
if( !user_angle ) {
// 定位质心
err = locate_centroids(farea, temp, shifts, size_x, size_y, &offset1);
if (err != 0) { return 2; }
/* Calculate the best fit line to the centroids */
err = fit(size_y, temp, shifts, slope, &offset2, R2, &avar, &bvar);
if (err != 0) { return 3; }
if (version)
MTFPRINT4("\nLinear Fit: R2 = %.3f SE_intercept = %.2f SE_angle = %.3f\n",
*R2, avar, atan(bvar)*(double)(180.0/M_PI))
}
/* Check slope is OK, and set size_y to be full multiple of cycles */
// 检查刀口斜率， 以确保后面超采样的质量
err = check_slope(*slope, &size_y, numcycles, cyclelimit, 1);
/* Start image at new location, so that same row is center */
// 调整ROI的行
center_row = *nrows/2;
start_row = center_row - size_y/2;
farea_old = farea;
farea = farea + start_row*size_x;
/* On center row how much shift to get edge centered in row. */
/* offset = 0.; Original code effectively used this (no centering)*/
// 计算刀口的偏移
if(user_angle)
offset = *off - size_x/2;
else
offset = offset1 + 0.5 + offset2 - size_x/2; // 为什么要加0.5？2019.03.26添加：因为dt是两个相邻点的关系， 所以dt的坐标应该加0.5
*off = offset;
if(version & ROUND || version & DER3)
offset += 0.125;
if (err != 0) { /* Slopes are bad. But send back enough
data, so a diagnostic image has a chance. */
*pcnt2 = 2*size_x; /* Ignore derivative peak */
return 4;
}
/* reference the temp and shifts values to the new y centre */
/* Instead of using the values in shifts, synthesize new ones based on
the best fit line. */
// 基于拟合结果更新shifts
col = size_y/2;
for (i=0; i < size_y; i++) {
shifts[i] = (*slope) * (double)(i-col) + offset;
}
/* Don't normalize the data. It gets normalized during dft process */
/* To normalize here, set dt = min and dt1 = max of farea data */
dt = 0.0;
dt1 = 1.0;
if (version & ESFFILE)
fp = fopen("esf.txt","w");
/* Calculate a long paired list of x values and signal values */
pcnt = 0;
for (j = 0; j < size_y; j++)
{
for (i = 0; i < size_x; i++)
{
edgex[pcnt] = (double)i - shifts[j]; // 计算每个点离刀口的距离
Signal[pcnt] = ((farea[((j*(long)size_x)+i)]) - dt)/(dt1-dt); // 归一化每个点的亮度
if ((version & ESFFILE) && edgex[pcnt] < size_x/2 + 3 && edgex[pcnt] > size_x/2 - 3)
fprintf(fp, "%f %f\n", edgex[pcnt], Signal[pcnt]);
pcnt++;
}
}
if (version & ESFFILE)
fclose(fp);
/* Allocate more memory */
bin_len = (unsigned int)(ALPHA*size_x);
AveEdge = (double *)malloc(bin_len*sizeof(double));
AveTmp = (double *)malloc(bin_len*sizeof(double));
counts = (long *)malloc(bin_len*sizeof(long));
/* Project ESF data into supersampled bins */
// 进行超采样， 生成长度为size_x*ALPHA（4）的单行图像(ESF), 保存在AveEdge中
nzero = bin_to_regular_xgrid((unsigned short)ALPHA, edgex, Signal,
AveEdge, counts,
size_x, size_y);
free(counts);
free(Signal);
free(edgex);
/* Compute LSF from ESF. Not yet centered or windowed. */
// 将ESF转换为差分图LSF， 并计算LSF的质心
if ( (version&DER3) )
calculate_derivative( bin_len, AveTmp, AveEdge, ¢roid, 1);
else
calculate_derivative( bin_len, AveTmp, AveEdge, ¢roid, 0);
if (iterate == 0) {
/* Copy ESF to output area */
for ( i=0; i