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Sharp feather tips can be approximated by adding smooth sine and cosine waves. This hummingbird’s outline is described by two Fourier series, one for each coordinate. Their rotating chains position the pen where the horizontal and vertical guides meet. Low frequencies capture the broad shape; higher frequencies recover smaller...

38,515 Aufrufe • vor 17 Tagen •via X (Twitter)

7 Kommentare

Profilbild von Peter MOUEZA🇲🇫
Peter MOUEZA🇲🇫vor 17 Tagen

By Fourier

Profilbild von Klaudivan
Klaudivanvor 17 Tagen

@threadreaderapp unroll please

Profilbild von Giovanni
Giovannivor 17 Tagen

love that. wow

Profilbild von Master Steward of New London
Master Steward of New Londonvor 17 Tagen

This is how they program drawing automatons, by the way

Profilbild von Ariz Ashraf
Ariz Ashrafvor 17 Tagen

Basically the first few waves just sketch the rough outline of the bird, then the higher ones fill in the sharp feathers and finer bits. Gets pretty accurate once you add enough of them.

Profilbild von TheRoloway
TheRolowayvor 17 Tagen

Using Fourier series to redraw a hummingbird outline is a beautiful way to show how low frequencies hold the shape and the high ones chase the feathers.

Profilbild von Nícolas Abreu
Nícolas Abreuvor 17 Tagen

@grok me explique o que tá acontecendo de forma leiga e resumida.

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Discrete Fourier Transform by hand ✍️ ~ 12 steps walkthrough below Here is a little-known secret about the DFT and the inverse DFT: it is just matrix multiplication in both directions, one the transpose of the other, exactly like the forward pass and backpropagation I drew in other examples. Goal: recover which cosine waves a signal is made of, using nothing but multiplication and addition. = 1. Given = Three signals written as sums of cosines, and a fourth, X, that we do not know yet. = 2. Frequency matrix F = Let us write the coefficients as a matrix. Each signal is a row, each frequency a column, so A = cos(w) + 2cos(2w) becomes [1, 2, 0, 0]. = 3. Sample the waves = We read the four cosine waves at ten discrete time points. That word "discrete" is the whole difference between this and the continuous transform. = 4. Cosine matrix W = Let us write those samples as a matrix: each frequency a row, each time point a column. = 5. Frequency to time = We multiply F by W. That combines the four cosine waves in the proportions F specifies, and the result T is the three signals as they would look in time. = 6. Transpose = Let us stand each signal up as a column. = 7. Time to frequency = We multiply W by that transpose. Every cell is the dot product of one signal with one cosine wave, which measures how much of that wave the signal contains. Zero means none of it. = 8. Scale = Let us multiply by 2/n, with n = 10. The projections come out five times too large, and this is the correction. = 9. Transpose back = We turn it back around, and it is F again, exactly. That is the check: the transform recovered the coefficients we started from. = 10. Now solve for X = Let us run the same multiplication on the one signal whose recipe we never knew. = 11. Scale = We divide by 5 again. = 12. Transpose back = And X reads [0, 0, 3, 2], which says X = 3cos(3w) + 2cos(4w). Note: I originally drew this to show that the DFT is a special case of a convolution layer, its filters fixed to sine and cosine waves rather than learned. No wonder, then, that a convolution layer free to learn its own filters can be trained to process signals. 💾 Save this post!

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