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A lot of people say that "what happens if I edit my RAW" or "do you lose RAW when you convert to jpeg" and I assumed that if a basic function such as file duplication (copy paste) was valid, they would not raise those concerns, which brings me to this question:

Can you duplicate RAW files without losing quality (as in, making an extra copy)?

  • One observation, Photoshop does not alter the RAW file in any way when you edit the picture. This might be the underlying concern of this question. – Wirewrap Feb 27 '16 at 19:29
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RAW files are digital data. Like all digital files, they can be copied exactly with no data loss.

You say

I assumed that if a basic function such as file duplication (copy paste) was valid, they would not raise those concerns, which brings me to this question

This doesn't logically follow. Because digital files are streams of discrete on-off bits (those 1s and 0s you always hear about), it's easy to copy them exactly — there's no question what the copy should look like. This is true no matter what is in the file: a RAW image, a JPEG, a music file, or a document. If there is an error in copying, it's detectable, because the sequence of on and off will no longer be exactly the same.

And, it's in contrast to what happens when you copy an analog source, like a cassette tape. There, the values which represent the data are stored with an infinite range of possibilities, and because reality is imperfect, you can't actually exactly read the value perfectly, or even exactly the same every time. That means every copy will introduce errors.

This is different from the errors introduced when saving in JPEG format. JPEG files are digital, too — ones and zeros — so they can be copied an infinite number of times with assurance that there are no errors. (Again, in the real world, data corruption is always possible, but with a digital file, you can easily do a perfect comparison, allowing detection of such errors.) The issue with JPEG is that, like MP3 music compression, there's a mathematical transform used to discard data which humans are less likely to notice. This makes the file (much) smaller, which is important for storage and transfer, but also is irreversible — once the file is compressed in this way, you can only get an approximation of the original back. And, in turn, it means that if you repeat this process, you'll throw away more information, successively getting worse.

But, RAW files are (almost always) compressed with simple lossless compression, or not compressed at all. That means this isn't a concern. And furthermore, most editing done on RAW files doesn't alter the original bits at all — it just stores a record of changes to be made, which your RAW editor can replay to recreate the same final image.

  • Might be worth emphasizing that RAW files aren't so much image files as they are dumps of data, as captured by a specific camera, and as such the conversion to even a "lossless" image format will generally involve the loss of some information. – junkyardsparkle Feb 27 '16 at 19:49
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    For that, let's refer to What is RAW, technically? For this question, I think the import point is that the content doesn't matter — all digital files can be copied with no loss or risk. – mattdm Feb 27 '16 at 21:55

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