Image processing artefact

The snap

The black surface in this snap looks much like the piece of black fabric that it is - with the instrument itself appearing in the previous post.

The thumbnail - enlarged

But on this laptop, the thumbnail that appears when you hover over the icon for the minimised image window on the task bar at the bottom of the screen, a thumbnail which is perhaps 4cm by 2cm appears, is striped. A thumbnail on which vertical stripes can clearly be seen, stripes which alternate light and dark, all more or less the same size and looking rather sinusoidal. Stripes which have - despite a glitch along the way - been preserved by the Microsoft screen capture function, then hopefully preserved by the Google image processing function and shown in an enlarged form above.

All very odd in that one usually expects image processing artefacts to appear when one enlarges an image beyond reason, not when one shrinks it. Although that said, one often gets odd effects in images with lots of lines going both up and down, as in a brick wall, a tiled roof or a shopping trolley. Has all this been triggered by the camera on my telephone registering the individual threads of the warp and weft of the fabric?

PS: and the stripes do indeed appear to have been preserved by Google, particularly if you click on the image to enlarge it.

Reference 1: http://psmv4.blogspot.com/2019/10/piano-31.html. The previous post.