Board Thread:Support Requests - Getting Technical/@comment-27494008-20160911214544/@comment-452-20160912140051

TheWearyandHeavyLaden wrote: I'm trying to replace old images on a Wiki because their file extensions should be .PNG and not .JPG. Please be aware that converting .JPG to .PNG is both pointless and severely frowned upon by people who care about quality.


 * JPG is a lossy format
 * PNG is a lossless format

If you're familiar with audio formats, JPG v PNG is equivalent to MP3 v FLAC. Converting MP3 to FLAC will get you shot in certain circles.

When people see the file extension, they know to expect a certain quality, converting a JPG to a PNG is ...make-up on a pig? ...wolf in sheep's clothing? ...if it quacks like a duck?

Converting a lossy format to a lossless format is like taking a photo of your computer screen when you want to "share" a photo instead of just saving and reposting the actual image. I know (old) people who actually do it, and it pains me that I can't convince them that it's "wrong", because they don't understand the concepts involved, and simply don't care. I'm unsure if it's to do with poor eyesight, or the fact they spent most of their lives with analogue TV, VHS, and still listen to crackly radio.

When I scanned their old photo collection and was showing them on my tablet, they proceeded to take photos of my tablet so they could send a copy to their friends. *facepalm*

TheWearyandHeavyLaden wrote:

I'm trying to replace old images on a Wiki because their file extensions should be .PNG and not .JPG. The purpose of that policy is likely because they want higher quality images. converting a JPG image to a PNG image does not increase the quality, and dilutes the quality of the wiki, by having low-quality images in a high-quality format.

I have a similar policy of using high quality PNGs where-ever possible, and if someone tried reuploading a JPG image converted to PNG, I would block them from the wiki, because that is vandalism.

Each format has a purpose, JPG is good for images and screenshots where pixel-perfect quality doesn't matter, and JPG artefacts aren't noticeable, such as photos of real life. Screenshots of movies and TV would also normally be JPG, because they're already compressed. For stills of video games and animation, it's sometimes better to use PNG, because JPG artefacts become more noticeable with this type of media.

Converting PNG to JPG for images which you don't need in pixel-perfect quality is a great way to save space, but converting existing JPG images to PNG should generally never be done in the way you're describing.

(Edit: There are exceptions, as noted below, such as if you're editing an image to add transparency, but I didn't originally mention it, because it wasn't relevant to your question.)