What quality setting should I use for a JPG?
Start at 90 and drop only if the file is still too large. 80 to 90 is where photographs are visually identical to the original but a fraction of the size. Below 70 you can see the 8x8 blocks in skies and gradients, and text and logos develop a shimmer around their edges. There is no undo: the discarded detail is gone from the file.
Why can I choose a background color?
Because JPEG cannot store transparency, so every transparent pixel has to be filled with something. White is the safe default, but if your PNG logo will sit on a dark header, filling with white gives it a bright halo along its anti-aliased edge. Set the fill to the color the image will really sit on.
Does converting to JPG twice make it worse?
Yes. Every JPEG save quantises the image again, and the damage compounds. Convert from your original file, not from a JPG you already made. This is why archival and working copies should be PNG or a raw format, with JPEG produced only at the final publishing step.
Should I convert a screenshot to JPG?
No. Screenshots are full of text and hard edges, which is the worst case for JPEG's compression: you get ringing artefacts around every letter, and the file is often bigger than the PNG would have been. PNG or WebP is the correct choice for screenshots, UI captures, and diagrams.
Will converting to JPG remove my photo's location data?
Yes. The image is decoded to a canvas and re-encoded, and a canvas holds only pixels. Every EXIF field, including GPS coordinates and camera serial number, is discarded. If you are publishing a photo, that is a genuine privacy improvement.
Why did the colors shift after converting?
Most likely the source carried a wide-gamut ICC profile (Display P3 from an iPhone, for example) that was dropped in the re-encode. The pixel values survive but are now interpreted as sRGB, which desaturates them slightly. If exact color matters, convert with a tool that embeds the profile.