Change pixels in subap, therefore is not outside the range.
When it is outside the range, it fails with a Segmentation fault such as:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffee6d4700 (LWP 889)]
copySubap (cstr=0x7fffe80c2d90, cam=0, threadno=<optimized out>) at rtccalibrate.c:365
365       tstr->subap[cnt]=(float)Hpxlbuf[i*npxlx+j];
                                            ^
                                            |___ here !