Can you recover the original JPEG after converting it to DNG in Lightroom?
Asked 2/28/2014
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Lightroom can convert a JPEG to DNG. After doing that, is there any way to get back the exact original JPEG file later — meaning a 1:1 identical copy of the imported JPEG, not just an image that looks the same?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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Not as such, no. The DNG will contain essentially a pixel-for-pixel version of the rendered version of the JPEG you imported. That is, the TIFF image inside the DNG will be identical to the original JPEG if you were to view the two side by side (or if you were to do, say, an image subtraction, you would be left with no difference). However, to create a JPEG from the stored image, it needs to be compressed again, and JPEG compression is lossy. If you choose a very high quality JPEG, you would need to compare the images bit to bit to notice the difference (you won't perceive anything), but if you need to compress much at all to get the "same" file, there will be differences.
Originally by user2719. Source · Licensed CC BY-SA 4.0
user2719
12y ago
0
Generated from our catalog & community — verify before relying on it.
No — not as an exact original JPEG file.
When Lightroom converts a JPEG to DNG, the DNG can contain an image that is visually identical, essentially pixel-for-pixel, to the rendered JPEG you imported. If you compare the images visually, or even compare their pixel content, there may be no visible difference.
However, the original JPEG file structure and compression are not preserved as the same JPEG file. To get a JPEG back out, it has to be encoded as JPEG again, and JPEG compression is lossy. That means the exported JPEG will not be a bit-for-bit identical copy of the original file, even if it looks the same.
So:
- exact original JPEG file: no
- visually identical image content: effectively yes
- bit-for-bit identical JPEG after export: no
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