This article is an in-depth explanation from my article “12 Photography Myths Every Photography Should Know.”
When photographers start debating the advantages of shooting RAW rather than JPEG, I inevitably hear that one advantage of shooting in RAW is that you can save it multiple times without reducing image quality.
In theory, this is absolutely true. Every time a JPEG image is saved, compression algorithms are run to reduce the file size. This means that some data is lost every time you make a change to the photo and save it. In contrast, RAW is what is called a lossless format. It makes no difference how many times you edit a RAW file, it will always contain the exact same data.
Without any doubt, the RAW format offers clear advantages over shooting JPEG. The most important of those advantages is the latitude to edit exposure and picture style. The added information in a RAW file makes editing much more successful.
However, I often find that photographers take this too far and imagine that saving a JPEG multiple times is doing more harm that it actually is. To see just exactly how much the pixels are altered buy saving a JPEG multiple times, I got one image and saved it out running compression on the image. Then I painted one pixel white on the file just so it wouldn't leave the file untouched, and then I took the resulting JPEG and repeated the process. In all, I saved the original photo 30 times.
Even after saving the photo 30 times, I found no noticeable reduction in image quality. None.
Granted, this test would certainly have turned out very differently if the test were performed while saving out lower quality JPEG images upon each save. In my testing, I saved the photo out as the maximum quality JPEG to prove my point. Clearly, this would not hold true if you save the photo in low quality.
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