PNG is useful for screenshots, logos and assets that need transparent pixels. It preserves the decoded pixel values through lossless encoding, though converting an already damaged source does not repair that source.
Convert Image to PNG produces a fresh PNG from a supported static image. It keeps the source dimensions and retains transparency that survives decoding.
Lossless does not mean smaller
A 400 by 300 source remains 400 by 300. If the source was JPEG, the new PNG preserves the decoded image, including any JPEG artefacts already visible in it.
Photographic detail can make a PNG much larger than the source JPEG. That is not a failed conversion. The formats use different ways to represent the image.
The tool uses a fixed PNG compression level rather than a lossy quality slider. Pixel dimensions are changed by resizing tools, not by pretending that a lower PNG quality will remove resolution.
Check transparent edges on more than white
The checker pattern in the preview indicates alpha. It is not part of the saved PNG. A dark background can reveal pale edge pixels that were difficult to notice against white.
If you later convert the PNG to JPEG, the alpha must be flattened onto a solid colour. Keep the PNG when the same asset needs to work over several different backgrounds.
Original metadata and colour profiles are not carried over. For a brand asset where exact colour management matters, retain the original and review appearance in the intended publishing system.
Choose PNG for what it preserves, not simply because the file extension sounds more professional. For a large photo under a strict byte limit, a carefully reviewed JPEG or WebP output may be a more practical choice.