Can Lightroom 5 perform lossless edits on JPEGs, such as crop or 90° rotation?
Asked 6/7/2014
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I’m wondering whether Lightroom 5 can apply any JPEG edits without recompressing the image data. Examples would include cropping, 90°/180° rotations, flips, diagonal transposes, or saving a small local edit while only recompressing the changed area. I’d prefer to stay in Lightroom so the edit history remains available, but I want to know whether these kinds of JPEG operations are actually lossless in Lightroom.
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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In general these operations are simply not possible to perform losslessly on a JPEG. Rotations are only mathematically possible when both the height and width of the JPEG are multiples of 8 or 16 pixels depending on chroma subsampling. You can read more about it here and here. If a website claims something else it's simply not true.
Regarding the other operations they are limited to the same constraints as explained in the links, the MCU:s (Minimum Coded Unit).
I'm not sure if Lightroom is capable of doing any of these operations even if and when they are mathematically possible, but if you're worried about how the program handles the problems and limitations that is a result of the architecture and design of the JPEG standard you're using the wrong format. Switch to RAW and transform it however you like and as a very last step export to JPEG as a finalised file and you won't have to deal with these problems at all.
Originally by user21986. Source · Licensed CC BY-SA 4.0
user21986
12y ago
0
Generated from our catalog & community — verify before relying on it.
Generally, no. JPEG is a lossy format, and so-called “lossless” JPEG transforms are only possible in limited cases because JPEG data is stored in MCU blocks (Minimum Coded Units). Operations like 90° rotations, flips, and some crops can only be mathematically lossless when the image dimensions and edit boundaries align with those JPEG blocks, which depend on factors like chroma subsampling.
The community answers do not confirm that Lightroom 5 performs these block-level lossless JPEG transforms, and in practice Lightroom is not the tool to rely on for that. If preserving maximum image quality through extensive edits matters, JPEG is the wrong source format for this workflow.
Best practice: use RAW when possible, then do your edits non-destructively in Lightroom. If you specifically need lossless JPEG transforms, you’ll typically need a dedicated utility designed for that purpose, and even then only supported operations under the JPEG format’s constraints will be truly lossless.
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