Please list his qualifications in refuting the PDF of BHOII's COLB.
Robert has failed to provide it, hence none.
Here is Tom Harrison's "report" upon which Corsi has apparently based his WND article.
http://www.wnd.com/files/2011/07/110726whitedots.pdf
Here is Harrison's "computer" business.
http://www.ts4.com/ As you can see, a grab-bag of handyman-type occupations. He can write you some scripted web sites or fix the fuel-pump controller in your Volvo. Here is the Google Maps readout of his "business" address -- a very nice-looking Oregon farmhouse, but not the office of a "computer expert."
https://maps.google.com/maps?f=q&so...382763,-122.557951&spn=0.003442,0.006534&z=18
His WND bio says he has a "background" in mathematics, physics, and computer science. (Hint: "background in" is faux bio double-speak for "takes an amateur interest in"). It also says he is a graduate of the liberal arts college Dartmouth, where he supposedly obtained a BA (not BS) degree in the above rigorous pursuits -- all in a brief 4 years (1972-1975). That would have been especially difficult since Dartmouth didn't offer a computer science degree until 1979. And while Dartmouth's engineering program is ABET accredited, its computer science program is not.
Harrison's "report" is riddled with ignorance and misconception.
...there are artifacts which cannot exist as the result of the scan of a paper document into a computer.
Indeed, they are the artifacts of optimizing the
PDF after scanning.
Indeed, those defending the document as genuine would have every citizen believe that the computer software responsible for scanning a simple piece of paper and converting it into a “pdf” file could not only see what was on the surface of that piece of paper, but could also see colors and detail underneath that paper surface, and that is an unashamed deception.
Nonsensical straw-man argument. Harrison doesn't understand the PDF imaging model and clearly hasn't attempted any PDF optimization exercises himself. Nor does he even raise the issue of what happens to portions of the image as they undergo optimization. Thus completely ignorant of those factors, in his mind the only factors that would determine the outcome of what he sees in the PDF objects would be the physics and optics of the scanner. Since they cannot explain what he sees, and his untrained imagination fails to consider any other reason, he concludes by default that it must be some kind of fraud or forgery.
This is simply the "finding" of a non-expert parading his ignorance in front of the world.
Now Harrison tries to explain a z-buffer rendering algorithm, such a that used in Photoshop. However that is not the algorithm used in PDF. Harrison has plainly not read the PDF language reference manual nor understands PDF's ideosyncratic clipping and rendering behavior. As with the other non-expert Mara Zebest, he simply believes PDF behaves as he sees layers operate in Adobe's creative products.
Typically, he "opens" the PDF in Adobe Illustrator and proceeds to attribute everything he sees in the imported document to some imaginary forger's actions, oblivious to any other potential cause.
On page 4 he commits a cardinal error in examining an optimized scanned PDF: he renders objects against a
different background. With his misconceived mindset that this was an image composed as layers in some other software, this makes sense. In the context of an optimized PDF of a scanned image, it is worse than nonsensical -- it's downright wrong.
Optimized PDFs of scanned documents are only expected to make sense visually when all the objects are rendered according to PDF's imaging model.
Specifically the optimization process happily copies elements between "foreground" and "background" objects freely, so that examining any one object results in seeing pixels from different logical parts of the document. For example, if you paint a background in Photoshop, type text over it, then paint some more in the foreground to obscure part of the text, the objects you get after you flatten, save, and optimize are the background, and then a "foreground object" containing all the pixels near the text, but
clipped by the text path. Three Photoshop layers become two PDF objects, where neither object bears any resemblance to one of the "creative" layers.
The bulk of Harrison's ignorance can be found in pages 5-7. In figures 3-5 he makes the mistake of turning on and off the clipping mask, not the object. He is astounded to find pixels "behind" the object he says is a foreground object in the (irrelevant) z-buffer stacking order. What he's seeing, of course, is the transparency and opacity applied to the background by the foreground clip as it accumulates in the PDF-style render, and shows the current graphics state pen color. In other words, he doesn't know what he's looking at.
The "white dots" are not supposed to be part of the visual document, they're the equivalent of a hold-out matte in optical compositing, from which the PDF rendering engine was conceptually derived. This is how object order in the render becomes irrelevant, whereas in a z-buffer method it's crucial.
As noted previously, some complex portions of an image are extracted and put in their own object because they are outlying (yet visually significant) elements in an indexed color space. That's what we have here. The "white dots" when masked out are simply the current pen color of the graphics context (not the color that's supposed to be displayed). The object is, instead, the smoothly-varying portion of the safety paper that couldn't be represented in the background object without an unacceptable error in the error-diffusion algorithm. You see in Fig. 5 that, with everything properly turned on, the image contains small variances in color and includes bluish hues that aren't in the mostly-green indexed color map.
Figs. 6-10 improve on Harrison's method if only in that he's turning the right objects on and off in Illustrator. (Put it this way, that error alone would disqualify him from expert status in court.) But again he fails to understand PDF's hold-out type rendering engine, and the optimization process. Again, the black hard-edged objects are single-value bitmasks that alternatively hold out the safety background object and clip the current pen color (black for some printed text in the Obama PDF, gray for others) for other objects.
However, Harrison does not realize that in order to
remove the black and gray pixels for the purpose of shrinking the color space for optimization, the pixels in the background object have to be
replaced with pixels that belong to the new indexed color space. Black and gray are not indexed colors in this image, so the optimizer filters them from adjancent pixels using a DCT method.
Naturally those pixels appear to be part of the background image because by definition the optimizer can only use colors already indexed as part of it. It's as if you are handed only green crayons and must color in all the spaces with them.
This is perfectly legal and appropriate in an optimized PDF, because it's supposed to make sense visually only when properly clipped and rendered as a whole page, not just as individual objects. Hence the replacement pixels are clipped away by the hold-outs in other objects.
Harrison simply has no clue. He patently does not understand the PDF rendering pipeline nor PDF optimization and hence has no knowledge of the underlying mechanisms that are working to produce what he sees in the resulting image. He wrongly thinks his critics have no more knowledge than he, so he concludes that the only way his critics can believe in that these pixels belong there in the PDF is if the scanner originally saw them that way -- i.e., in "x-ray fashion." No, this is
not what his critics believe, and he's simply throwing a ridiculous straw man into the fray.
As does Zebest, Harrison argues that since "magic" scanners don't exist, the only way you'd get friendly pixels in the "layers" in the "background" is if they came from some graphics program such as Photoshop that let an artist compose in layers, knowing that foreground layers would obscure the background where appropriate.
However on page 1 Harrison deftly sidesteps the smoking gun. He says that he is undertaking this analysis without any attempt at contextual or larger-scale framing. And with that he ignores the same glaring, egregious hole in his claim that Zebest does: that the "foreground" text is divided half between the "background layer" and half between the "text layer".
Basically, Tom Harrison is patently not an expert and his analysis further ignores practically everything about PDF files that is pertinent. It is as wrong as it can possibly be.