Wallpaper on a TV or a projector
The same file, spread across two metres of wall, stops being the same picture.
A monitor sits half a metre away and measures sixty centimetres across. A projector puts the same number of pixels on two metres of wall, and a television is watched from three metres back. The file does not change, but the distance between neighbouring pixels does, and a sky that looked smooth on a desk can show its compression as wide, soft steps once it has been enlarged.
Light matters more here than resolution. A projector can only add light to a wall, never subtract it, so black arrives as whatever grey the room allows, and a dark, spare wallpaper that looks composed on a laptop turns into a dusty rectangle. A bright room does something similar to a television, where reflections settle on top of the shadows. Images that carry their contrast in colour rather than in darkness survive both rooms.
The edges deserve a thought too. Some televisions still trim a few percent of the frame, and ambient modes re-encode whatever you hand them, so a subject pressed against the border can come back shaved. What works on a wall is usually quieter than what works on a desk: fewer fine details, and nothing that asks to be read from across the room.
