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Someone has converted a number of JPG's to BMP's, and then to PNG, under the assumption that it will "increase quality". Of course, it doesn't, as once you've introduced lossy compression you can never get anything "better" than that.

So now the problem is, BMP's are big. I can use lossless formats like 24bpp PNG, but they are still bigger than the "original" JPG's, despite being identical images.

Is it possible to return those BMP's back to JPG's without introducing additional artifacts? My impression is no, but maybe I'm wrong?

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  • I suspect no, because the artefacts introduced when the jpeg was created will be interpreted and compressed again. You could use very high quality jpg but they will end up bigger than png probably. I am guessing these aren't photos? Can you post a sample? – Paul Dec 13 '13 at 3:53
  • I think this would apply to all JPG images in general, unless there are certain conditions where a JPG -> BMP -> JPG process can actually recover the "original" JPG. – That Umbrella Guy Dec 13 '13 at 12:23
  • Sure - but the result of a displayed jpg is a bitmap approximating the original bitmap. The approximation is based on the quality setting. If you jpg your bmps with a high enough quality, the resultant jpg should be indistinguishable from the original jpg, except in the size of the output file. Which would be big. – Paul Dec 14 '13 at 22:09
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No, doing so - at least with any JPG compression - will introduce additional quality loss as you suspected. The only question is how much. It may be possible to recompress them without further noticeable loss, but they will be "less true" to the original then the BMP

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