Reading Arithmetic Coded JPEG Files Is Not Implemented

While writing the previous post, I found myself being lazy and wanted to dig up an image to use instead of taking a screenshot of the error message myself. Finding one, I proceed to download it for editing in photoshop, however I was unprepared for the error I was about to find.

“Could not complete your request because reading arithmetic coded JPEG files is not implemented.”

What!? A quick Google search yields a possible answer. png_hexPerhaps the image file I had was using an incorrect extension for its actual type! The forum post lists gif, so I change my extension to gif. Nope. Okay, time for the good old fashioned hex editor. I open up the file in Notepad++ and look at the header information. What was that? Right there at the top? PNG! I have found the problem.  A quick extension change later and I was on my way to throwing the file into Photoshop.

Note on the featured image: I took an existing image and typed some gibberish into the hex code which corrupted the image. Instant artifacts!

Source for solution


Agent[31] works in the IT field for a living. He enjoys a wide variety of interests from music to photography to computer games. He wants to share the joy he finds with others.

  • nightshade.FX

    this is not helpful at all

    • Actually, the information in this article is completely accurate, but the author has perhaps made an assumption on how to do something you might not be familiar with.

      The problem is simply that an image has been given a file extension that doesn’t match its file type. A file’s extension is the (usually) three letters after the last full stop in a file’s name e.g. “.jpg” or “.doc” or “.pdf” and so on. This tells the computer what kind of file it is and is normally always set by the program creating it, and so is normally always correct. So Word will always save a document with “.doc” on the end, Acrobat makes “.pdf” files etc. Images are slightly more complex because there are so many different format types (JPG, TIFF, PNG, GIF to name a few you might be familiar with) but which to the average user all look the same and all appear to do the same job. In reality, they are all very different in terms of how they store the image information. You can Google these formats to see what the differences are, but for this purpose it doesn’t really matter.

      What has happened in this case, is that an image file of one type (PNG) has been mistakenly been given the file extension of another (JPG). Photoshop (rather stupidly, in my opinion) is basing its actions purely on the file extension it sees and trying to open the file as a JPG, which of course doesn’t work because the image data is actually stored as a PNG. If you manually change the file’s extension from “.jpg” to “.png” then you should find the image opens just fine. I found this post because I’ve just had the exact same error message in Photoshop, and fixed it in exactly the way I just described.

      What a professional-level piece of software should do (again, in my opinion) is look at the file’s actual data and try to be a bit smarter about how to deal with it. I could open the image in question using a $20 piece of shareware (GraphicConverter on the Mac, but there are similar Windows utilities) but apparently $500+ a year isn’t enough for Adobe’s programmers to actually look a the file’s header information.

      • nightshade.FX

        no, i meant that he doesn’t say how to actually fix the problem in the article BECAUSE IT DOESN’T WORK. however, you are telling me how to do the exact OPPOSITE of what i want to do, and it doesn’t work the other way either.

        • Agent31

          The problem that I ran into was as Ian mentioned. The filetype that I tried to open was not what it claimed to be. In my instance changing the file extension (from .jpg to .png) solved the issue and allowed Photoshop to open the file which was incorrectly named. Without knowing what your problem was there’s no way to offer you a solution but I’m glad to hear you resolved it on your own.

        • Agent31

          I also realize that I didn’t write this article as a guide but more of an “oh, look what happened here!” post. If you need a guide I could always write up the detailed steps with pictures, etc.

        • Given that you’ve never actually stated what your problem was, it’s kind of hard for anyone to help, and very easy for you to yap “UNHELPFUL!!” in angry caps lock.

      • nightshade.FX

        plus, i already fixed the problem, anyway

  • bumpershine

    If you pulled it off your iPhone, there is a good chance it is .mov file, not a .jpg file. iPhones sometimes encode “live photos” as .jpg when they really should be .mov files.