DCT Normalization - possible bug

[ACDC77]

Hi Dmitrii,

When computing DCT type III (inverse of DCT type II), for 2D formatted data, the configuration.normalize setting seems to have no effect on the output. The output I see is always unnormalized regardless of whether this field is 0 (default) or 1. Could you please try to replicate at your end?

Here are my configuration settings:

config_idct.FFTdim = 2;
config_idct.size[0] = N;
config_idct.size[1] = M;
config_idct.performR2C = false;
config_idct.isInputFormatted = true;
config_idct.isOutputFormatted = true;
config_idct.kernelConvolution = 0;
config_idct.doublePrecision = 0;
config_idct.numberBatches = 1;
config_idct.performDCT = 3;
config_idct.normalize = 1;

Regards,
Atul

[DTolm]

Hello,

the normalize parameter only affects the IFFT - meaning the plan has to be launched with 1 passed as the inverse parameter in VkFFTAppend. All forward transforms are currently unnormalized. So to get normalized DCT-III, you need to launch IDCT-II plan created with normalize flag.

Best regards,
Dmitrii

[ACDC77]

Thanks @DTolm. I changed the config_idct to the one shown below with DCT type as 2 and normalize = 1, and called VkFFTAppend with 1 (for inverse FFT). Now the results of the inverse DCT are normalized.

config_idct.FFTdim = 2;
config_idct.size[0] = N;
config_idct.size[1] = M;
config_idct.performR2C = false;
config_idct.isInputFormatted = true;
config_idct.isOutputFormatted = true;
config_idct.kernelConvolution = 0;
config_idct.doublePrecision = 0;
config_idct.numberBatches = 1;
config_idct.performDCT = 2;
config_idct.normalize = 1;

initializeVkFFT(&app_idct, config_idct);
VkFFTAppend(&app_idct, 1, &params);

Appreciate the help.