Scale used: the information bar at the bottom of input.tif (rows ~962-1023) contains a scale bar labelled "1 um". The bar is 53 px wide (columns 1202-1254), so 1000 nm / 53 px = 18.9 nm per pixel (field of view about 24 um wide). The TIFF has no pixel-size metadata (only a default 72 dpi), so the scale bar was used. I did not decode the magnification text.

Method: cropped out the info bar, removed the background with a Gaussian high-pass filter, applied a Hann window and computed the 2D FFT. The dominant peak pair lies at a spatial period of about 47 px (neighbouring peaks 46-49 px; radial-profile maximum at 46.5-48.8 px), which is about 890 nm (range about 860-930 nm).

Orientation: the FFT peaks lie along the horizontal frequency axis (about 3 degrees off it). The periodicity is therefore horizontal, and the ridges/lines run approximately vertically in the image, tilted about 3 degrees from vertical.

RESULT: period = 890 nm
