How the target-size search works
Rather than guessing a quality value, Aimager runs a binary search: it encodes the image at different quality levels, measures the real byte size, and homes in on the best quality that still fits under your target. If even the lowest quality is too big, it automatically downscales the dimensions.
When a target can't be met
Some limits are physically impossible for a given image - for example a huge photo forced under 10 KB. Aimager tells you clearly when it can't reach the target instead of silently destroying the picture.