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To: Polarik
You didn't really answer my question, so let me phrase it a little more clearly. What if one document was scanned at 1000*2000 pixels and saved. The other was scanned at 4000*8000 and resized to 1000*2000 and saved. Both files are now the same size, but they would not be identical because the one that went from 4k*8k to 1k*2k would have some information thrown out by the computer, and the information that was not thrown out would not necessarily as the one that was scanned in at 1k*2k to begin with. Try it.

Also, does your argument in the OP hinge on the forger using an 8-bit graphics program? That is pretty darn far fetched.
95 posted on 07/16/2008 5:15:49 PM PDT by itsPatAmerican
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To: itsPatAmerican

Thanks for making it clearer, but I would have preferred if you presented just the request for clarification without adding the condescending remark to it.

I think what you’re saying is that a JPG made directly from scanner output would “look better” (or have fewer pixel artifacts) than a JPG of a JPG.

Answering this question is a bit difficult without actually testing the scanner and software used to produce the new COLB scan.

As front-end users of scanning software, we usually do not know which algorithms the scanner software uses to go from a bitmap in memory (produced at the time of scanning and subsequently displayed in a preview) to a 25% reduction, and then to a JPG file.

For the moment, let’s assume that this process is “better” than doing a JPG to JPG reduction.

Actually, we can do an analogous test using the latest COLB. I will do a fourfold reduction in size as in your example, but with 5100 x 6600 instead of 4000*8000.

What I did was to take the original JPG image of the COLB, which was a full-sized, direct save from the scanner’s bitmapped image, and convert it to a full-size, 24-bit bitmap file (100MB in size).

It will not exactly be the same as the bitmap produced by the scanner (for the reasons cited above), but it gives us the same starting point for the test.

So, now we have a bitmap of 5100 x 6600 pixels that represents what the scanner might have initially produced.

From that 100% bitmap, I saved it as a JPG with a 25% reduction.

Also From that 100% bitmap, I saved it first as a full-size JPG, resized it to 1275 x 1650, a 25% reduction, and saved that as another JPG.

The results produced two JPGS from which I cropped two images, that were very close in size and dimensions, from the upper left corner of the COLB (where it reads STATE OF HAWAII & HONOLULU).

The full-size image files were too big to upload, and these clips provide enough info for comparison purposes.

I’m going to let you (and anyone else) be the judge here.

Here are the links:

http://i305.photobucket.com/albums/nn227/Polarik/hawaii-a.jpg

http://i305.photobucket.com/albums/nn227/Polarik/hawaii-b.jpg

OK, now which one is the direct, full-sized bitmap to a 25% JPG, and which one is the direct, full-sized bitmap to a full-sized JPG to a 25% JPG.

And, please explain your answers. This quiz will not affect your final grade in this course. :-)

BTW, people, I’m going offline until Monday evening, so please do not think I’m ignoring anyone’s comments made during this time period.


99 posted on 07/17/2008 10:59:55 AM PDT by Polarik (obama, birth certificate)
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