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Darius Kazemi

TIL that JPEG encoding in the wild is even more complicated than the very complicated documentation makes it out to be. For example, most references I can find say that the difference between an RGB and a CMYK jpeg is the former will have 3 "components" and the latter 4. This in theory should be encoded in a particular start-of-frame byte. And yet I have seen images detected as CMYK by ffmpeg have "03" in that byte position. And there are reports of CMYK jpegs that are really RGB under the hood?

20 Dec 2023 at 18:01 | Open on friend.camp
10 comments
Craig P

@darius If so, that'd be super annoying. We sorta rely on CMYK jpegs for printing...

20 Dec 2023 at 18:02 | Reply | Open on mastodon.social
Darius Kazemi

The other thing I learned today is I truly love when my job requires me to bust out a hex editor to inspect file encodings

20 Dec 2023 at 18:06 | Reply | Open on friend.camp
allison

@darius i have like three different gameboy roms and save dumps open in hex editors right now and it makes me feel like an important hacker 💻

20 Dec 2023 at 18:14 | Reply | Open on friend.camp
Darius Kazemi

@aparrish all I want is to manually count offsets and go "oh that's A7 and I was expecting A6! Interesting...."

20 Dec 2023 at 18:16 | Reply | Open on friend.camp
Martyn

@darius my first programming job required me to read files from an acorn on a DOS/windows system. Shifting bits, reading strings backwards and doing actual mantissa and exponent maths. Those were the days...

20 Dec 2023 at 18:38 | Reply | Open on toot.martyn.berlin
jmac

@darius Absolutely the best moments of my day job are when I see the database I’m documenting do something really weird, and I start *digging*.

20 Dec 2023 at 19:44 | Reply | Open on masto.nyc
JP

@darius also does it look cool when you view an RGB JPEG as CMYK or vice versa (or is that not possible given the different strides + amounts of expected data)

20 Dec 2023 at 18:17 | Reply | Open on mastodon.social
Shawn Medero

@darius The most fun I had working on HTML5 (in the most tiny of roles, btw) was when people would bring stuff like this to the working group and I'd get to go dive into the archives of the internet trying to reverse engineer the decision making that led us to the state we were in. 99% of the time there was never ill intent - some implementation was left with a bunch of bad choices and the people responsible picked the one they thought would cause the least harm.

20 Dec 2023 at 18:57 | Reply | Open on friend.camp
Eli the Bearded

@darius I've never read the JPEG spec. Still about 18 years ago I tried to get a CMYK JPEG into a more easily usable format. I wrote up my adventures in learning about the format here:

qaz.wtf/jpeg/

20 Dec 2023 at 19:51 | Reply | Open on fed.qaz.red
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