What a Wallpaper Weighs
Compression gives itself away in the sky long before it touches the leaves.
A wallpaper is the picture you see most often and study least. It sits at full size behind everything, unmoving, with no caption and nothing to compare it against. That is a strange kind of exposure: whatever is wrong with the file has the whole day to be noticed, usually in the second between closing one window and opening the next.
Compression fails where the image is smoothest. A sky at dusk, a wall out of focus, fog thinning toward the horizon — these are long gradients, and a small file turns them into steps, faint bands the eye finds once and then keeps finding. A forest hides the same compression without complaint, because leaves are noise and noise covers its own tracks. The quiet photograph is the expensive one.
So the trade is not really size against quality; it is size against emptiness. A few megabytes cost nothing on a drive that holds a hundred thousand photos, and the larger version of a gradient is worth taking, at the screen's own resolution, saved once rather than re-saved. On a desktop, quality is not sharpness. It is the absence of anything the eye can pick at while it waits.
