[gentoo-user] Re: [OT] Saving an image as black and white
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 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 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 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
[gentoo-user] Re: [OT] Saving an image as black and white
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 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 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
Re: [gentoo-user] Re: [OT] Saving an image as black and white
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 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 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 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 >
Re: [gentoo-user] Re: [OT] Saving an image as black and white
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 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 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 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
