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On 2021-03-01, Wols Lists wrote: |
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|
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> I've got a bunch of scans, let's assume they're text documents. And |
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> they're rather big ... I want to email them. |
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> |
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> How on earth do I convert them to TRUE b&w documents? At the moment they |
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> are jpegs that weigh in at 3MB, and I guess they're using about 5 bytes |
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> to store all the colour, luminance, whatever, per pixel. But actually, |
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> there's only ONE BIT of information there - whether that pixel is black |
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> or white. |
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> |
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> I'm using imagemagick, but so far all my attempts to strip out the |
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> surplus information have resulted in INcreasing the file size ??? |
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> |
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> So basically, how do I save an image as "one bit per pixel" like you'd |
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> think you'd send to a B&W printer? |
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> |
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> Even at 300dpi, I make that 300*300/8 ~= 10KB/in^2 or 800KB of |
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> uncompressed info for a page of A4, not 3MB. |
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> |
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> Cheers, |
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> Wol |
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|
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Somebody else might have a better suggestion, or perhaps a better |
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understanding of the JPEG format and of what needs to be tuned, but, for |
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example: |
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|
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convert origin.jpg -threshold 70% -monochrome result.jpg |
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|
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(And adjust the "-threshold percent" if needed. It might be that you |
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don't need thresholding at all, but if you do, it apparently must go |
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before "-monochrome".) |
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|
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(Depending on the receiving end, you could also explore other |
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formats. Here, if the scanned document can be stored in monochrome, I |
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usually use djvu.) |
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|
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-- |
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Nuno Silva |