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Beginner
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MKL FFT and Inverse FFT

Dear. Intel Members

I gottwo answers from intel engineer about MKL FFT and Inverse FFT

but I got a problem.

from first answer. Ican get a right forward FFT signal about our data. but I can get a inverse data

(Our data consist of 14bit WORD type so I usemy data transfer to float)

from second answer.I canget a correct Inverse data But I can't use FFT Data because some different

things compair malab result.

below is your two answer.

and I attached1 file about your answer result

this issue is very urgent

If you able Please answer ASAP

Thanks~

All the Best

1.

int i,j;

const int ROWS=3072, COLS=2560;

const int ROWSIZE=COLS, COLSIZE=ROWS;

_complex *xx = new _complex[ROWS*COLS];

memset(xx,1,2*sizeof(float)*ROWS*COLS); /* zero fill initialization */

int r,c;

for(r=0;r

{

for (c=0;c

{

xx[*ROWSIZE+(c)].x = (img[*ROWSIZE+(c)]);

xx[*ROWSIZE+(c)].y = (img[*ROWSIZE+(c)]);

}

}

int Height_f = ROWS;

int Widtht_f = COLS;

DFTI_DESCRIPTOR_HANDLE rowfft;

DFTI_DESCRIPTOR_HANDLE colfft;

MKL_LONG status;

MKL_LONG l[2];

float src;

//////////////////////////////////////////////////////////////////////////////////

DftiCreateDescriptor(&rowfft, DFTI_SINGLE, DFTI_COMPLEX, 1, ROWSIZE); /* stride 1 by default */

DftiSetValue(rowfft, DFTI_NUMBER_OF_TRANSFORMS, (MKL_LONG)ROWS);

DftiSetValue(rowfft, DFTI_INPUT_DISTANCE, (MKL_LONG)ROWSIZE);

DftiSetValue(rowfft, DFTI_OUTPUT_DISTANCE, (MKL_LONG)ROWSIZE);

DftiCreateDescriptor(&colfft, DFTI_SINGLE, DFTI_COMPLEX, 1, COLSIZE); /* will set strides */

MKL_LONG colfft_strides[] = {0, ROWSIZE};

DftiSetValue(colfft, DFTI_INPUT_STRIDES, colfft_strides);

DftiSetValue(colfft, DFTI_OUTPUT_STRIDES, colfft_strides);

DftiSetValue(colfft, DFTI_NUMBER_OF_TRANSFORMS, (MKL_LONG)COLS);

DftiSetValue(colfft, DFTI_INPUT_DISTANCE, (MKL_LONG)1);

DftiSetValue(colfft, DFTI_OUTPUT_DISTANCE, (MKL_LONG)1);

status = DftiCommitDescriptor( rowfft);

DftiComputeForward(rowfft, xx);

status = DftiCommitDescriptor( colfft);

DftiComputeForward(colfft, xx);

2. Second Answer

#define x(r,c) x[*ROWSIZE+(c)] /* explicit row-major indexing */

typedef struct {float x,y;} singlecomplex;

const int ROWS=3072, COLS=2560;

const int ROWSIZE=COLS, COLSIZE=ROWS;

singlecomplex* xx;

xx = (singlecomplex *)malloc(2*sizeof(float)*ROWS*COLS); /* zero fill initialization -> Ones pading */

memset(xx,0,2*sizeof(float)*ROWS*COLS); /* zero fill initialization */

int r,c;

for(r=0;r

{

for (c=0;c

{

xx[*ROWSIZE+(c)].x = (img[*ROWSIZE+(c)]);

xx[*ROWSIZE+(c)].y = (img[*ROWSIZE+(c)]);

}

}

int Height_f = ROWS;

int Widtht_f = COLS;

DFTI_DESCRIPTOR_HANDLE rowfft;

DFTI_DESCRIPTOR_HANDLE colfft;

MKL_LONG status;

MKL_LONG colfft_strides[] = {0, ROWSIZE};

float src;

status = DftiCreateDescriptor(&rowfft, DFTI_SINGLE, DFTI_COMPLEX, 1, (MKL_LONG)ROWSIZE); /* stride 1 by default */

status = DftiSetValue(rowfft, DFTI_NUMBER_OF_TRANSFORMS, (MKL_LONG)ROWS);

status = DftiSetValue(rowfft, DFTI_INPUT_DISTANCE, (MKL_LONG)ROWSIZE);

status = DftiSetValue(rowfft, DFTI_BACKWARD_SCALE, 1.0/(ROWS*COLS));

// status = DftiSetValue(rowfft, DFTI_OUTPUT_DISTANCE, (MKL_LONG)ROWSIZE); // not needed for in-place

status = DftiCreateDescriptor(&colfft, DFTI_SINGLE, DFTI_COMPLEX, 1, (MKL_LONG)COLSIZE); /* will set strides */

status = DftiSetValue(colfft, DFTI_NUMBER_OF_TRANSFORMS, (MKL_LONG)COLS);

status = DftiSetValue(colfft, DFTI_INPUT_DISTANCE, (MKL_LONG)1);

// status = DftiSetValue(colfft, DFTI_OUTPUT_DISTANCE, (MKL_LONG)1); // not needed for in-place

status = DftiSetValue(colfft, DFTI_INPUT_STRIDES, colfft_strides);

// status = DftiSetValue(colfft, DFTI_OUTPUT_STRIDES, colfft_strides); // not needed for in-place

status = DftiCommitDescriptor( rowfft);

status = DftiComputeForward(rowfft, xx);

status = DftiCommitDescriptor( colfft);

status = DftiComputeForward(colfft, xx);

// ///Inverse FFT

status = DftiCommitDescriptor( colfft);

status = DftiComputeBackward(colfft, xx);

status = DftiCommitDescriptor( rowfft);

status = DftiComputeBackward(rowfft, xx);

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5 Replies
Highlighted
Valued Contributor I
23 Views

Hi,

The difference between these two variants is in using normalization of trnasforms:

status = DftiSetValue(rowfft, DFTI_BACKWARD_SCALE, 1.0/(ROWS*COLS));

But also please correct your second variant which is not currently correspond to what wassuggested to you.

I means, not needed DftiCommitDescriptor callsafter line // ///Inverse FFT.

Maybe something else was not corrected by you.

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Highlighted
Beginner
23 Views

Hi

Thanks to your fast answer

your answer:

I means, not needed DftiCommitDescriptor calls after line // ///Inverse FFT.

-> It is just test code. When I use inverse FFT I don't call DftiCommitDescriptor


Already I attachedmy result file.

I testmy code usingyour code(first code), and your engineer code (2).

Result of FFTusing first code I can see frequency. so I can calculate something.

but I can't get a incerse FFT image.

general, As I know FFT + inverse FFT -> Original image (if I don't treat anything)

by your 1 code I test fft and Inverse fft but I can't get a original image.

When I using code 2

in this case I can get FFT + incerse FFT = original image

but in the FFT image, I can't see the signal. and I cant calculate frequency.

my needs : FFT -> find frequency position information and some calculate and inverse fft

all the best

Dakin

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Highlighted
Valued Contributor I
23 Views

Dakin,

Looks like it was you who startedthread about The FFT adjusts only half size...

And that root cause was in interpretation/visualization of data after FFTs. So, please double check your testcase again.

Anyway, it will benice to see your self-contained testcase to reproduce your new problem in order to help you.

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Highlighted
Beginner
23 Views

Victor

you are right my issee Start from FFT harf size .

I also test from harfsize test. I also same result only harf size result and can't get inverse FFT image

by sample code in the Intel MKL manual.

fortunately I can get a kind and nice answer from you soI can get a full size FFT result (I can see frequency information) butcan't get a inverse FFT

Another member give a one clue normalization so I can get a FFT and IFFT but I can't get frequency information data

I also check my project and code again and again.

If you have a clue.

Please advice for me.

I'm very thanks to your kindness and help

all the best

Dakin

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Highlighted
Valued Contributor I
23 Views

Dakin,

Please add checking of DFTI status after all DFTI calls to be sure that all is OK.

E.g. see MKLROOT/examples/dftc

if (! DftiErrorClass(Status, DFTI_NO_ERROR)) {
printf(" TEST FAILED : after ....)\n");
failure++;
goto FREE_DESCRIPTOR;
}

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