Tiff to JBIG2 PDF?

[dowcet]

I have a bunch of scanned monochrome images like this:

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input.tif TIFF 3184x5276 3184x5276+0+0 1-bit Bilevel DirectClass 104KB 0.000u 0:00.000

I want to make a PDF which will not be so large. From what I understand JBIG2 compression is the best available for monochrome PDFs. So I tried this:

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convert input.tif -compress JBIG2 -density 300 output.pdf

Despite the much lower resolution, the resulting file is actually a little bit larger (and 16-bit):

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output.pdf PDF 764x1266 764x1266+0+0 16-bit Bilevel DirectClass 122KB 0.010u 0:00.010

What am I doing wrong?

[snibgo]

I don't know much about compression within PDF files. You might try all the "-compress" options to see which is the best.

[dowcet]

@snibgo: Thanks, that is a great suggestion.

I started off with a black/white PNG called bilevel-image.png

identify -verbose bilevel-image.png

Image: bilevel-image.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: PseudoClass
Geometry: 3100x4746+0+0
Units: Undefined
Colorspace: Gray
Type: Bilevel
Base type: Undefined
Endianess: Undefined
Depth: 8/1-bit
Channel depth:
gray: 1-bit
Colors: 2
Compression: Zip

I produced all the PDFs with the command:

for a in $(convert -list compress); do convert -compress $a bilevel-image.png bilevel-image-$a.pdf; done

and then checked the compression used by the PDF and added the PDF's size for comparison.

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B44A          /RunLengthDecode    757266
B44           /RunLengthDecode    757264
BZip          /RunLengthDecode    757266
DXT1          /RunLengthDecode    757266
DXT3          /RunLengthDecode    757266
DXT5          /RunLengthDecode    757266
Fax           /CCITTFaxDecode      98604
Group4        /CCITTFaxDecode      98610
JBIG1         /RunLengthDecode    757268
JBIG2         /RunLengthDecode    757268
JPEG2000      /JPXDecode         2067778
JPEG          /DCTDecode         2436412
LosslessJPEG  /RunLengthDecode    757282
Lossless      /RunLengthDecode    757274
LZMA          /RunLengthDecode    757266
LZW           /LZWDecode          325225
None          /ASCII85Decode    17038912
Piz           /RunLengthDecode    757264
Pxr24         /RunLengthDecode    757268
RLE           /RunLengthDecode    757264
RunlengthEncoded /RunLengthDecode 757290
WebP          /RunLengthDecode    757266
ZipS          /RunLengthDecode    757266
Zip           /FlateDecode        311026
Zstd          /RunLengthDecode    757266

/RunLengthDecode is clearly the default, used when the desired compression cannot be.

JBIG2 /RunLengthDecode 757268

probably means that the JBIG2 libraries are not available.

Generally JBIG2 gives by far the best bilevel compression.