Sampling, and the pattern you get instead
A periodic pattern, the samples kept from it, and the only pattern those samples describe. The defaults are a real measurement: the ribbed table in this unit's photograph runs at 7.385 pixels per cycle.
Try this
Leave the period at 7.385 and walk the sampling interval from 1 to 8. Nothing happens until you pass 3, and then the reconstruction detaches from the signal completely — at 8 a 7-pixel ripple comes back 96 pixels wide. Nudge the period to 7.4 and that answer moves to 99: folding multiplies any error in the period by the sampling interval.
Where this lab comes from
Sampling: What One Pixel Covers, and What Falls BetweenLesson 2 of The Image as Data. One photosite on this camera is 5.527 µm and covers 1.056 arcminutes of the room. The table in the frame is ribbed at 7.4 pixels per cycle; keep every 8th pixel and it comes back at 96 pixels per cycle — thirteen times too coarse, and predicted exactly by folding the frequency.
More in the image itself
- One colour per photosite — Throw away two thirds of the colour, then guess it back.
- Hitting the colour a meter measured — Drag the gains and watch ΔE against 22 metered patches.
- Sixteen by twelve real pixels — Hover a pixel, read its index and its three numbers.