Why convert JPG to PNG?
The main reason is editing. Each time a JPG is saved, a little more detail is lost. Converting to PNG first means you can crop, annotate and re-save as many times as you like without adding new compression damage. Some tools, templates and upload forms also accept only PNG.
Converting does not undo compression that is already in the JPG. Any blockiness or softness in the original carries over exactly as it is, because PNG copies the pixels faithfully.
JPG vs PNG: which should you use?
JPG uses lossy compression, which makes photos small but softens sharp edges. PNG is lossless and supports transparency, which makes it better for logos, screenshots, diagrams and anything with text. For photos, PNG files are usually several times larger than the JPG they came from.
So keep photos as JPG for sharing, and use PNG for graphics or as a working copy while editing. If you need a small file with transparency, WebP is often the better choice.
Does converting to PNG make the background transparent?
No. JPG has no transparency, so the background in your photo is ordinary pixels, often white. The PNG will have the same background. To remove it, use the Remove Image Background or Make Background Transparent tools, which save a PNG with a transparent background.
How to convert JPG to PNG
Upload a JPG. The conversion starts right away, and the preview shows the PNG with its size and dimensions next to the original. The dimensions stay the same, and the photo is turned upright if its orientation tag says it was taken sideways. For many files at once, the Bulk Image Compressor can save up to 20 images as PNG in one ZIP.