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On 01/03/21 12:11, (Nuno Silva) wrote: |
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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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Thanks but no, I've already tried that. It makes matters worse! |
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I've messed about with the scanner, so it is now creating 800KB images, |
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but I don't want to rescan everything I've done. |
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|
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The problem is that it is clearly saving the images as greyscale, not as |
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black&white. And when I search for help, what I want is swamped by all |
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the false positives for greyscale. |
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Oh - and for Nuno - sorry tesseract is no use, they are NOT text. That's |
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why I used the word "assume" - to make it clear that I want a |
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1-bit/pixel palette, not a 5-byte/pixel greyscale. |
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|
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Cheers, |
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Wol |
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