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