Dowa / server-side signal processing

Fourier Image Lab

Upload an image, inspect its spatial and frequency domains, then isolate a rectangle in either domain and reconstruct the filtered result.

Choose an image

Choose a PNG, JPEG, BMP, or GIF. The C server decodes it into a 64 by 64 luminance grid and performs every transform and filter. Files must be 20 MiB or smaller.

Choose an image to begin.

Spatial domain Luminance samples sent to the transform.

Frequency domain Centered logarithmic magnitude spectrum.

Inverse transform Image reconstructed after both filters.

Spatial crop

Drag on the image, edit the coordinates, or focus the image and use arrow keys to move the crop. Hold Shift with an arrow key to resize it. Press Space or Enter to toggle the filter.

Keep only this spatial region

Width

Height

Frequency crop

Drag on the image, edit the coordinates, or focus the image and use arrow keys to move the crop. Hold Shift with an arrow key to resize it. Press Space or Enter to toggle the filter.

Keep only this frequency region and its conjugate

Width

Height

What is happening

The server decodes the uploaded image with its bounded image library. Dowa then applies a two-dimensional fast Fourier transform to the selected spatial samples. Frequency filtering keeps the chosen coefficients and their conjugates so the inverse remains a real image, and the server returns all three 64 by 64 planes in one bounded response.