Scale used: the information bar of the 1280x1024 image (rows ~964-1023) contains a scale bar 53 px long (x = 1202..1254) labelled "1 um". That gives 1000 nm / 53 px = ~18.9 nm per pixel (the TIFF metadata only has a dummy 72 dpi, so it was not used). The magnification text in the bar was not needed.

Analysis: the SEM area (rows 0-959) was background-flattened, windowed, and a zero-padded 2D FFT taken. There is one dominant peak pair at about 27 cycles across the 1280 px width, i.e. a period of ~47.2 px (47.0-47.4 px depending on peak vs centroid estimate; sub-windows in three of four quadrants give 45.7-47.3 px). 47.2 px x 18.9 nm/px = ~890 nm (about 0.9 um; uncertainty roughly +/-5 percent, mostly from the scale-bar length of +/-1 px and the peak width).

Orientation: the spatial-frequency vector lies along the image x axis (within ~3 degrees), so the periodic structures are stripes / ridges running essentially vertically in the image (parallel to the y axis, with a slight tilt of ~2-3 degrees), repeating horizontally.

RESULT: period = 890 nm
