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On 01/03/21 13:48, Neil Bothwick wrote: |
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> On Mon, 1 Mar 2021 11:50:35 +0000, 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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> $ convert input.jpg -threshold 50% output.png |
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> |
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> should do it, you may need to play with the threshold setting. The file |
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> command reports the output file as being "1-bit grayscale". |
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> |
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> You can also use -monochrome but that will produce a dithered image, |
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> that's probably not what you want judging by your description. |
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> |
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> |
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FINALLY! |
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Thanks, that worked! Okay, I also adjusted the dpi because the original |
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scan was 600 and I've reduced it to 300, but this has reduced the file |
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size from 3MB to 180KB. |
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Dunno why, but everything I was trying was INcreasing the file size :-( |
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And the png does make a massive difference - the same command with jpg |
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output is 1.7MB - so why is my scanner chucking out 800KB jpegs if I set |
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it correctly? |
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|
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Cheers, |
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Wol |
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