unsigned char idata[1400][1400]; //working fine
    unsigned char idata[1600][1400]; //not working

unsigned char** idata = new unsigned char*[DIM1];

for (int i = 0; i < DIM1; ++i)
    idata[i] = new unsigned char[DIM2];

// or

unsigned char (*idata)[DIM2] = new char[DIM1][DIM2];

unsigned char** idata = malloc(sizeof(unsigned char*) * DIM1);

for (i = 0; i < DIM1; ++i)
    idata[i] = malloc(DIM2);

// or

unsigned char (*idata)[DIM2] = malloc(DIM1 * DIM2);

unsigned char (*idata)[1400] = malloc(1600 * 1400);
// ...
free(idata);