Revisiting Diffraction with an Apodized "Iris"

Started Aug 15, 2017 | Discussions thread
Joofa Senior Member • Posts: 2,655
Re: Discrete Cosine Transform and DFT

alanr0 wrote:

AiryDiscus wrote:

is jpg FT or discrete cosine transform? (Curious, I am not sure -- perhaps DFT and DCT are even related)

JPEG uses Discrete Cosine Transform.

DCT is a DFT of discretely sampled real quantity, which is assumed to be symmetric about the origin.

DFT of a real symmetric function is real, and contains only cosine terms.

There are several flavors of DCT. The 'standard' DCT and DFT of the same sequence are related by a formula. A reason that DCT is used in JPEG over DFT is that it provides more 'energy compaction' than DFT, which helps in more signal compression.

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