For photographs
JPG is a practical option for photos when the destination accepts it. Its quality setting lets you trade some detail for a smaller file. Compare the result rather than expecting a fixed saving percentage.
PNG can also store photographs, but the file may be much larger. Choose it when you need PNG specifically, rather than assuming that conversion improves a photo.
For text and transparent graphics
PNG is often useful for screenshots, diagrams, and graphics with sharp edges. Its lossless compression can preserve the stored pixel data. Reducing a PNG palette before saving is a separate change that can alter colours.
JPG does not support transparency. When you convert a transparent PNG to JPG in Filecozy, those areas receive a solid background colour. Use PNG or WebP if the transparent background is needed.
Conversion cannot recover missing detail
Converting JPG to PNG preserves the decoded JPG image without adding another lossy encoding step. It does not remove artifacts already present in the JPG.
Before downloading, check whether the destination accepts the format, whether transparency is correct, and whether the file meets its size limit. Keep a copy of the source.