I was confused with a different concept, disregard that part. FFT is by definition reversible for a discrete signal like a quantized image so each pixel must be reversible, so it has to be 4x total space used with no further operation, correct.<p>Quantization and filtering are the more important parts of the encoder than the FFT &#x2F; DCTs since the transform is 1:1 reversible. Compression isn&#x27;t just the mathematical accuracy of a signal when it comes to lossy algorithms as you know. A 720p video upscaled to 1440p should theoretically be exactly the same size for the sake of effective quality but encoders don&#x27;t care about just the math and apply perceptual filters because simply doubling pixels looks really bad perceptually it turns out.