This chapter describes the Intel® IPP image processing functions that
perform linear transform operations on an image buffer.
These operations include Fast Fourier Transform (FFT), Discrete
Fourier Transform (DFT), and Discrete Cosine Transform (DCT).
To speed up performance, linear transform functions use precomputed
auxiliary data that is needed for computation of the transforms (that is, tables of
twiddle factors for FFT functions). This data is calculated by the respective
initialization functions and passed to the transform functions in context structures
specific for each type of transform.
Intel IPP linear transform functions can use external work buffers for
storing data and intermediate results, which eliminates the need to allocate and free
internal memory buffers and thus helps to further increase function performance. To
determine the required work buffer size, use one of the respective support functions
specific for each transform type. In case when no external buffer is specified, the
transform functions handle memory allocation internally.
All Intel IPP linear transform functions except DCT of 8x8 size work
on images with floating-point data only.