save/convert to pdf - use gs from ghostscrpit to convert them (I use ebook for the target) which gives 10-20x reduction in size with only a small reduction in quality - perfect for emailing.
I dont have the actual command string but I originally found the suggestion via google. BillK On 1/3/21 9:17 pm, Wols Lists wrote: > On 01/03/21 12:11, (Nuno Silva) wrote: >> 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.) >> > Thanks but no, I've already tried that. It makes matters worse! > > I've messed about with the scanner, so it is now creating 800KB images, > but I don't want to rescan everything I've done. > > The problem is that it is clearly saving the images as greyscale, not as > black&white. And when I search for help, what I want is swamped by all > the false positives for greyscale. > > Oh - and for Nuno - sorry tesseract is no use, they are NOT text. That's > why I used the word "assume" - to make it clear that I want a > 1-bit/pixel palette, not a 5-byte/pixel greyscale. > > Cheers, > Wol >
