An educational moment

Our friend Hermitian is responding to my findings that the Xerox created documents contain JPEGs with embedded comments in them. I found such comments in the WH PDF as well as the WH Tax Form PDF used to scan in the President’s tax returns… Of course, this is quite strong data in support of my hypothesis. So what does Hermitian do?

Yup ! It figures that Xerox would plant a useless comment in all their JPEGS.

It is irrelevant why Xerox would put comments in their JPEGs, one can speculate but the fact is that they do. They have no impact on how the file is rendered, they are just a tag added by the JPEG creation software used by Xerox.

I wonder why Preview would leave it in there ?

This is best understood when realizing that Preview is not a JPEG editor or bitmap editor. You can manipulate PDF objects but Preview does not touch the embedded image Xobjects. This makes a lot of sense because it has no reason to resave them. In fact, resaving a JPEG as JPEG may lead to additional quality reductions, even when saved at full quality. But one can do the experiment and print a JPEG to PDF and then extract the JPEG and look at the metadata. It remains exactly the same.

 

2 thoughts on “An educational moment

  1. NBC

    “It is irrelevant why Xerox would put comments in their JPEGs, one can speculate but the fact is that they do. They have no impact on how the file is rendered, they are just a tag added by the JPEG creation software used by Xerox.”

    HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

    As I pointed out to you before, it is you who are claiming that this YCbCr tag is unique to Xerox. Therefore it is up to you to prove your claim. Since, to date, you have provided exactly zero proof to back up your claim then I don’t give it much weight. Especially when the YCbCr color space is the “ONLY” one permitted under JFIF. Now here’s why. Xerox may have added the comment as a reminder that the PDF meets the JFIF standard. If so it’s very unlikely that Xerox’s competitors wouldn’t do likewise just for marketing reasons. Or maybe Xerox buys the JPEG compression from a third party who also supplies the same software to others.

    You could have easily backed up you claim just by closing the loop with Xerox. But then you haven’t. You could saw off all the jawboning back and forth with one phone call.

  2. As I pointed out to you before, it is you who are claiming that this YCbCr tag is unique to Xerox. Therefore it is up to you to prove your claim.

    Actually, the burden is on you to show that I am wrong. I cannot prove a negative but I can do a search of all the jpegs I have downloaded. Until then the finding that the two documents contain the same comment embedded is quite strong evidence. Until of course disproven. That’s where you come in.

    You could have easily backed up you claim just by closing the loop with Xerox. But then you haven’t. You could saw off all the jawboning back and forth with one phone call.

    Xerox cannot tell me if others do not use the same comment. Silly Hermetian…

    You too could make the phone call. I am quite unconcerned about the why…

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