size of an scanned image

size of an scanned image

Postby bflorin11 » Wed Sep 10, 2008 1:42 am

Hello,

I have a general question about the size of a scanned image.
I took a A4 page and I scanned it in 300 DPI in black&white. If we make the calculus we have 8.3 * 11.7* 300 = 29133 bits of information (which tell us if the point is black or white).
This makes:
29133 / 8 = 3641 bytes / 1024 ~ 3 kb. We can assume that there are some extra headers and that the total will not be more than 4kb. When I scan a TIFF with CCITT group 4 in 300 DPI in black&white from an A4 page I get often more for the size of the files. How is it possible? Did I misunderstand something?

Thanks,
Florin
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Postby russell@centuryc.com » Wed Sep 10, 2008 12:01 pm

It's 300 pixels per linear inch, not square inch.

So, (8.3 * 300) * (11.7 * 300) = 8,739,900 bits.

That's uncompressed. G4 will compresses that down considerable under most situations. The end result will depend on how many black/white and white/black transitions there are in a image. Therefore G4 filesize is a function of complexity.

I would expect an all white and an all black image it be about the same size.
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Postby bflorin11 » Fri Sep 12, 2008 12:22 am

indeed. thanks!

Best regards,
Florin
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