There's a certain JPG image I want to replace with the PNG version so that the uncompressed art is more readily open for viewing on this site, but the uploader keeps saying that it's a duplicate of the inferior version.

Is there a method for updating the image file or is it pretty much stuck that way?

sins_and_virtues said:
There's a certain JPG image I want to replace with the PNG version so that the uncompressed art is more readily open for viewing on this site, but the uploader keeps saying that it's a duplicate of the inferior version.

Is there a method for updating the image file or is it pretty much stuck that way?

If the upload form says that it's a duplicate of the inferior version, then the two files match each other exactly.
That check is not exactly intelligent, even the slightest changes will prevent it from going off.
(There can be exceptions, but those are incredibly rare)

What is the post you are trying to replace, and where did you find the file you are trying to replace it with?

bitwolfy said:
What is the post you are trying to replace, and where did you find the file you are trying to replace it with?

It would happen to be this one below:
post #1882606

And the file I'm trying to replace it with is this one but as a PNG: https://d.furaffinity.net/art/lonbluewolf/1558789193/1558789193.lonbluewolf_drw4.png

sins_and_virtues said:
It would happen to be this one below:
post #1882606

And the file I'm trying to replace it with is this one but as a PNG: https://d.furaffinity.net/art/lonbluewolf/1558789193/1558789193.lonbluewolf_drw4.png

Oh, I have asked about this before.
To quote from a message I received from @Mairo a few years back in regards to this,

Mairo said:

... Furaffinity is just bit gamble of what the file actually is and e621 will properly rename the file extension to match the filetype. If furaffinity does state JPG file to be PNG, that usually means original uploaded file was indeed PNG, but you'd have to go to artists computer to get it as furaffinity destroys that copy.

Essentially, the one on FA and on e6 are both the same files, even though the file type differs.
You can check this by downloading the original source file from FA and the one on e6, putting them both through the MD5 File Checksum (a tool to see if files are the same), and then comparing the MD5 hash they both produce.
Both of the files will return 79c059e4b5636e2dacbb8411c61ffe3e, which is also the file name for the download from e6.

sins_and_virtues said:
It would happen to be this one below:
post #1882606

And the file I'm trying to replace it with is this one but as a PNG: https://d.furaffinity.net/art/lonbluewolf/1558789193/1558789193.lonbluewolf_drw4.png

To expand on what @TheGreatWolfgang said:

FurAffinity downscales larger uploads to 1280px, and converts them to JPEG. There is a way to bypass it, but if the artist does not use it, then the original version is effectively destroyed.
The stated extension has no bearing on the actual file format. You can achieve the same result by downloading the file from e621, and changing the extension manually to .png – it won't stop being a jpeg file.

Besides using a MD5 checksum utility, a quick way to see if the files are identical would be to look at their filesizes – if they are identical, then the files most likely also match.
(Note that one file being larger does not necessarily mean that it's better, just that it's different)

I see. Thanks for the answers!