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  #71  
Old 07-24-2010
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Quote:
Originally Posted by lydanynom View Post
Well, again, if you mean "opinion" in the sense that there might be other equally correct answers then, no, in fact. It's not a value judgment, it's just math.
Howww! That's quite a statement. Are you a professional photographer or a professional in digital image treatment? Your certitude is really impressive since you seem to be discussing the subject with a professional and a teacher on that area of knowledge.
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  #72  
Old 07-24-2010
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The discipline most relevant to what we've been talking about is digital forensics.
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  #73  
Old 07-24-2010
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Originally Posted by lydanynom View Post
Well, again, if you mean "opinion" in the sense that there might be other equally correct answers then, no, in fact. It's not a value judgment, it's just math.
I really don't care for you delivering a lecture at me about how digital imaging works, or about whether or not my statements conform to your approval.
If you want to discuss the whale, fine.
If you want to discuss digital imaging, suggest you try any of the photographic forums. You have a nice theory on reverse engineering raw files. Let's see some application of that theory. Otherwise it's just so much smoke.

This would be a good resource for you...
Forensic Photoshop

Again, I'm going to suggest that you have a nice day on your boat.
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  #74  
Old 07-24-2010
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Originally Posted by tomwatt View Post
You have a nice theory on reverse engineering raw files. Let's see some application of that theory. Otherwise it's just so much smoke.
It's already a well documented topic in the peer-reviewed journals, Tom, and there are a lot of applicable transcripts from conferences as well. If you're interested in it then you need to start by getting a basic knowledge of the low level structure of the format, as I mentioned above, so that you are thinking about this in more literal terms rather than in the abstractions that you seem to be used to.

If you're not interested I certainly understand, but in that case I can't figure out why you still want to try to argue about it.

Last edited by lydanynom; 07-24-2010 at 02:55 PM.
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  #75  
Old 07-24-2010
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Originally Posted by lydanynom View Post
It's already a well documented topic in the peer-reviewed journals, Tom, and there are a lot of applicable transcripts from conferences as well. If you're interested in it then you need to start by getting a basic knowledge of the low level structure of the format, as I mentioned above, so that you are thinking about this in more literal terms rather than in the abstractions that you seem to be used to.

If you're not interested I certainly understand, but in that case I can't figure out why you still want to try to argue about it.
I'm not going to attempt to lay out the flaws in your discussion points, it's summer, school is out, and I have bigger fish to fry. Strongly suggest you check your own eye for motes before pointing to splinters in other's eyes.

Have a nice day on your boat, sir.
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  #76  
Old 07-24-2010
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Originally Posted by tomwatt View Post
I'm not going to attempt to lay out the flaws in your discussion points
Probably a good decision.
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  #77  
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Originally Posted by lydanynom View Post
Probably a good decision.
It's clear that none of us on this forum are nearly smart enough to compete with your logic and mathematics. So rather than argue, or to keep coming back to your feebly-put points, let me ask some questions so that you can enlighten those of us who are not so bright.

1) You stated that DCRaw can be used to resave a raw file, making the implication that any changes made would then be undetectable. You have seen this or just read it in a paper online? Because a good follow-up question would have to be undetectable by whom? Software engineers that know nothing about image-making except for doing the numbers?

All I have seen so far of DCRaw and it's companion open-source software indicates that it can access and translate a raw file, not reverse engineer one, given the proprietary nature of camera raw file formats, that would be an excellent trick. If you've got that down pat already, I'd be happy to point you towards several software companies who would pay a pretty penny for such a thing.

2) You have repeatedly stated that my assertion was too broad... again this is in your opinion... since you seem unable to see that, I suggest you have someone aboard to help you steer your vessel in the future, at least until you can have your eyes checked.

3) You state that I am making assumptions but you are just talking facts. Numbers. Logic. Kindly explain:
Quote:
I'm assuming you're talking about the raw file here and assuming a camera that is capable of saving one and that was configured to do so, but even given all of that how would you tell the difference between a file straight out of the camera and one saved in the camera's raw format by desktop software?
4) Referencing again the above-mentioned quote regarding saving a camera raw file using desktop software... again, you know a software that makes a change to the raw file that is permanent and undetectable? Please enlighten us. Enquiring minds want to know.

5) If this is a dig at me, you are in poor form, sir. This kind of statement leads me to wonder if mommy forgot to bring you your snack down there in the basement.
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"You are not entitled to your opinion. You are entitled to your informed opinion. No one is entitled to be ignorant."
6) The following quoted statement contains serious errors. A raw file is a copy of the information captured by the sensor, along with other camera data. Image processing software "develops" the image but even resaving a raw file should make no alteration to the original data capture. Just to the interpolation instructions. Again, those are camera-proprietary. And the information is UNprocessed. It is raw data from the sensor. The magic of camera raw is in being able to change the color space without any change to the original file. So changing color temperature is seamless, but reversible.
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There's nothing magic or immutable about a raw file, it's just in a huge color space and not very processed. The exif data is trivial to alter, and the only way it can be returned to "as shot" with a click is if it has been manipulated using tools supporting those non-destructive methods. If the actual bits are flipped then the actual bits are flipped. Forging one is a slightly higher bar than forging a more accessible format, but not by a whole lot.
7) In the statement below, you have managed to read my mind to know what it is I know and don't know. I'm hungry, could you please let me know what it is I want for dinner?
Quote:
a raw image is just another bucket of bits on your hard drive. There are tens of proprietary formats, almost all of them just offshoots of the tiff container, and nothing is magic about any of them. You are assuming that because the desktop software you use and teach with every day edits them non-destructively that these files are inherently immutable, but that is no more true for those image files than it is for video files I edit in an NLE.
8) So help me understand your statement below, you think that just because you read that if it goes one way, it can go the other and be undetectable? Staying on the dinner topic, I had a nice steak last night which I'd be happy to bring up for you.
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There are several open source packages that read virtually all raw formats, most notably dcraw. If I know how to read a raw file, perform the demosaic, compress the dynamic range, transform into the target colorspace and etc, then I also know how to go the other other way.
I have no doubt that somewhere in the world, there is a talented programmer who can write the program extensions to open source software to be able to generate a raw file that resembles something like a camera generates. However, since a reasonable person looking at the circumstances of the whale/boat impact in a reasonable way would have to conclude that the talent pool to generate such a fake is fairly small, and that it would be reasonable to exclude that as a possibility. That was the case in my earliest - and in your opinion too broad - posting.

And even more reasonably, one would likewise have to conclude that anyone with the time talent and skills to reverse engineer a camera raw file to fake the incident would comprise an even smaller pool of individuals, since the file would need to correctly emulate the characteristics of the camera alleged to have been used. Additionally, the file would need to survive visual examination for space continuity, perspective, color, light & shade. That's a bit of a chore. Not hard for the average art school graduate, but a lot of work nonetheless.

I'd love to read your answers to my questions and comments, since I need to learn so much more about this area, and you are obviously so well-informed.

In the interim, let me wish you a prolonged anchorage next to the "Crazy Frenchman of Portobelo Bay."
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  #78  
Old 07-24-2010
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Quote:
Originally Posted by tomwatt View Post
1) You stated that DCRaw can be used to resave a raw file
No, just that it is an example of a large, functional codebase to start from.

Quote:
2) You have repeatedly stated that my assertion was too broad... again this is in your opinion...
No, if you are still making it unequivocally, it isn't. A raw image alone is not enough to prove authenticity. This has been my only point all along.

Quote:
4) Referencing again the above-mentioned quote regarding saving a camera raw file using desktop software... again, you know a software that makes a change to the raw file that is permanent and undetectable?
Nope, you are correct. This was a sloppy, oversimplified way for me to put it. As far as I know there is no commercial software that will do anything like that.

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5) If this is a dig at me, you are in poor form, sir.
The Ellison quote was in no way directed at you.

Quote:
6) The following quoted statement contains serious errors. A raw file is a copy of the information captured by the sensor, along with other camera data. Image processing software "develops" the image but even resaving a raw file should make no alteration to the original data capture. Just to the interpolation instructions. Again, those are camera-proprietary. And the information is UNprocessed. It is raw data from the sensor. The magic of camera raw is in being able to change the color space without any change to the original file. So changing color temperature is seamless, but reversible.
I don't know, man, there are a lot of problems with much of what you are saying there. There is too much to really go over every detail, that's why I keep suggesting you look into the file structure on your own, but one of the biggies is the idea you keep returning to that the raw file itself can't be changed. When you use lightroom or whatever to manipulate a file, the changes are reversible because they are stored as a set of instructions appended to the raw data. A lame psuedo-example:

*file*0101010101010101010101*end file*
*change white point*
*change gamma curve*

But it only works that way because the software plays along. If I want to alter the raw file permanently then I just change the raw data directly:

*file*0000000111111111010101*end file*
*change white point*
*change gamma curve*

So there is nothing about the file itself that makes it immutable. In contemplating a forgery, the devil is in the details of writing back the missing data in a way consistent with the hardware, as you mention below, but this is the topic of extensive discussion and research in forensic circles and a ton of lab work has been published.

The point, my point, has just been that you can't look at raw image as some kind of gold standard, that's all.

Quote:
I have no doubt that somewhere in the world, there is a talented programmer who can write the program extensions to open source software to be able to generate a raw file that resembles something like a camera generates.
I would not have put it quite so singularly, but this is essentially all I have been saying.

Quote:
However, since a reasonable person looking at the circumstances of the whale/boat impact in a reasonable way would have to conclude that the talent pool to generate such a fake is fairly small, and that it would be reasonable to exclude that as a possibility. That was the case in my earliest - and in your opinion too broad - posting.
I'm not sure I understand this paragraph. Are you saying that you have been speaking only in the context of this whale image and not making blanket assertions regarding raw files in general? If so, I did not correctly understand you. I was never talking about the whale image myself as in my opinion there was ample evidence that it was not a forgery from the beginning.

Last edited by lydanynom; 07-24-2010 at 06:40 PM.
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