How can I tell which of two JPEGs is closest to the original and preserves the most detail?
Asked 8/17/2019
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I have multiple JPEG versions of the same photo with different resolutions, file sizes, and metadata, and I want to know whether one is likely to be the original from an iPhone and, if not, which version preserves the most information. Is there a reliable way to determine this from JPEG metadata alone, or by comparing the files?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
4
You can't really tell from these data. Of course, one could hope that the bigger file holds a bit more information, but it could just be the other one badly re-encoded. Utilities such as ImageMagick's identify can tell you the JPEG "quality" setting (and the chroma sub-sampling) but you can still be looking at a re-encoding that caused some data loss.
If you have both images, you can:
- convert them both to PNG
- reencode the PNG to JPG with the same settings for all
The bigger file will now correspond to the initial picture with the more "information" (but, strictly speaking, this could be added noise).
Originally by user75947. Source · Licensed CC BY-SA 4.0
user75947
6y ago
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You usually can’t determine the true original from JPEG metadata alone. A larger file or higher resolution may contain more detail, but it could also just be a re-encoded or resized copy.
A few practical clues:
- If the dimensions don’t match the camera’s native output, it’s probably not the original.
- Shared images from Apple devices are often resized, especially when emailed or otherwise exported.
- A higher-resolution version is usually more likely to be closer to the original than smaller copies.
To compare two JPEGs you already have, a practical method is:
- Convert both JPEGs to a lossless format like PNG.
- Re-save both PNGs to JPEG using the exact same settings.
- Compare the resulting file sizes and visual detail.
After normalizing the JPEG settings, the image that produces the larger JPEG is often the one that retained more information originally. This is not perfect, because noise or sharpening can also increase file size.
If you truly need the original, the best option is to get it directly from the device or from the person who owns it.
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AI6y ago
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