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I know that you lose quality going to a lossy format.

Examples:
flac > mp3
ogg > mp3

But do you lose quality going from it?

Example:
mp3 > flac

Bonus question: What about images?

Example:
jpg > png
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1 Answer

up vote 9 down vote accepted

Nope.

When you convert from FLAC to MP3 (or whatever formats), the converter has to essentially re-record the file. It would be like taking a video of a video, or taking a photo of a photo; of course you're not going to maintain the quality of the original.

However, when you convert from MP3 to FLAC, you're simply decompressing the MP3 and taking the raw sound of whatever is there. No quality loss. Of course, as James Polley pointed out in the comments, you can't gain quality out of nothing in this way.

This applies to audio, video, images, etc.

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Cool. Glad to here it. Can you please supply a reference of some sort? – Daniel H Dec 31 '09 at 4:51
4  
But you also won't gain any quality: the conversion can't put back what isn't there. If you convert from a lossy format to a lossless format and then back to a lossy format, you'll usually have lost quality compared to your original lossy-format file. – James Polley Dec 31 '09 at 4:51
1  
@James: Of course not. Who said you'd gain any quality? ;) – Sasha Chedygov Dec 31 '09 at 4:52
Lossy formats, by definition, do not lose data - they contain the full data of the file. They're a 1:1 representation of the sound that comes out of your speakers, or the image displayed on your screen. – James Polley Dec 31 '09 at 4:53
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To make it clearer: in order to play the audio, or display the image, the original file has to be converted to a lossless format for output. Once it's in that lossless format, saving it in a lossless format does not lose any data. – James Polley Dec 31 '09 at 4:54
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