Aspect-Ratio Visualizer

The two percentages are the same fact told from opposite ends. Fitting inside reports how much of the frame gets used; filling it reports how much of the picture survives, and a frame filled 75% by the one is a picture 25% cut away by the other. They always add up, which is worth knowing before you go looking for a setting that improves both.

The stretch figure is literal rather than descriptive. When the readout says a circle becomes an ellipse 1.333 times as wide as it is tall, 1.333 is the axis ratio of the shape actually drawn on your screen, sized from the same arithmetic rather than illustrated beside it. That is why a number close to 1 looks like nothing happened: it did not.

A shape is recognised by name within about half a percent, so 1920x1080 comes back as 16:9 widescreen. Outside that tolerance you get the plain numbers rather than a name, which is the more useful answer: 1.9:1 is not 16:9, and rounding it into one would hide the very difference you came to measure. Only the relationship between the two numbers is ever read, so 3840x2160 and 1920x1080 are the same shape here and a resolution is never a size.

This is geometry, and it is not a preview. It never opens your picture: the rectangles are the two shapes drawn at a readable size, not your image scaled into a frame. So it can say how much is lost and along which axis, and it cannot say what is lost. Whether filling the frame takes someone out of the shot is a question about the picture rather than about its shape, and nothing you type here leaves the page, because there is nothing to send.

cargo build --release --bin aspect-cli