JPG, PNG or WebP: which image format to choose and when to convert
There is no single best format for everything. JPG, PNG and WebP solve different needs. Choosing well avoids unnecessarily large files, quality loss or transparency problems.
JPG: usually practical for photographs
JPEG uses lossy compression. That can greatly reduce the size of a photograph, although each new compression can discard image information. It does not support transparency. It is a common choice when you need broad compatibility and a reasonably small photo file.
PNG: transparency and lossless preservation
PNG uses lossless compression and supports transparency. It is often suitable for graphics, screenshots, logos and images where you need crisp edges or an alpha channel. For complex photographs it can produce files much larger than a lossy format.
WebP: flexible for the web
WebP supports lossy and lossless compression, transparency and animation. Google documents that in its comparisons WebP can produce smaller files than JPEG and PNG at comparable visual quality. Even so, converting an image does not always guarantee a smaller file: the result depends on the source content and selected quality.
Photo: JPG or WebP. Transparency or crisp graphics: PNG or WebP. If a service does not accept WebP, convert it to the compatible format you need.
Conversion does not restore lost quality
Converting a JPG to PNG does not restore details lost when the JPG was compressed. The file may become larger, but discarded information does not return. Likewise, repeatedly converting between lossy formats can progressively degrade the image.
What happens to transparency
PNG and WebP can preserve transparency. JPG has no alpha channel. If you convert a transparent image to JPG, transparent areas need to become a background color. The Rusadix converter uses white so the result is predictable.