From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by finch.gentoo.org (Postfix) with ESMTPS id 5BF621382C5 for ; Mon, 1 Mar 2021 12:48:36 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 43852E0999; Mon, 1 Mar 2021 12:48:31 +0000 (UTC) Received: from ciao.gmane.io (ciao.gmane.io [116.202.254.214]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 03623E098E for ; Mon, 1 Mar 2021 12:48:30 +0000 (UTC) Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lGhyP-0006LO-Du for gentoo-user@lists.gentoo.org; Mon, 01 Mar 2021 13:48:29 +0100 X-Injected-Via-Gmane: http://gmane.org/ To: gentoo-user@lists.gentoo.org From: (Nuno Silva) Subject: [gentoo-user] Re: [OT] Saving an image as black and white Date: Mon, 01 Mar 2021 12:48:25 +0000 Message-ID: References: <603CD50B.9080303@youngman.org.uk> <603CE962.7070202@youngman.org.uk> Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org X-Auto-Response-Suppress: DR, RN, NRN, OOF, AutoReply Mime-Version: 1.0 Content-Type: text/plain User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) X-Archives-Salt: 41de6be2-7261-43ce-b14c-89fafbdfe24c X-Archives-Hash: fead281e7615b63ddea5f7adca22a4d0 On 2021-03-01, 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 Sorry, my bad - I was checking the file sizes, but I didn't notice the larger one was the new, "monochrome" version. More coffee needed, it seems. -- Nuno Silva