Forums - Transformations and warpings, how to use them?

Hi Paula, 

The function transforms a canonical 8x8 rectanlge centered at 0,0 to a region in the image and samples in that small region. 

nPos[2] is the translation component of the affine transform in 32 bit fixed point 

affine[2][2] is the rotation and scaling component also in 32 bit fixed point. 

Below is a code snipet that shows how the function can be used.

static inline int float2Fx32( float nFloat )

{

    int fixed = ( int )( nFloat*( 1<<16 ) );

    return fixed;

}

static void float2Fx32( float * nFloat, int* fixed,int size )

{

   for ( int k = 0; k < size; k++ )

   {

      fixed[ k ] = float2Fx32( nFloat[ k ] );

  }

}

  float posf[2], matf[4];

  posf[ 0 ] = 12.25f; posf[ 1 ] = 52.0f;

  matf[0] = 0.013717344f; 

  matf[1] = 0.69070274f; 

  matf[2] = -0.67423344f;

  matf[3] =  0.024732463f;

  //Make sure arrays are 128 bits aligned

  int FASTCV_ALIGN128(posi32[2]), FASTCV_ALIGN(mati32[4]);

  float2Fx32( posf,posi32,2 );

  float2Fx32( matf,mati32,4 );

  unsigned char FASTCV_ALIGN128(img[480*320]);

  unsigned char FASTCV_ALIGN128(patch[8*8]);

  int res = fcvTransformAffine8x8u8( img,480,320, posi32, mati32, patch);

 Cheers,

 Guy

The above code provides a very good description of using the TransformAffine8x8 function and should work as expected. In general, whenver there is a byte mis-alignment (of size 4, 8, 16), one can use the following FastCV macro functions to align the data properly:

FASTCV_ALIGN32 // macro to align memory at 4 bytes (32 bits)

FASTCV_ALIGN64  // macro to align memory at 8 bytes (64 bits)

FASTCV_ALIGN128 // macro to align memory at 16 bytes (128 bits)

Thanks!