preearth.net/imagemagick/

@snibgo: Thanks, that is a great suggestion.

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

[color=blue]identify -verbose bilevel-image.png[/color]

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:

[color=blue]for a in $(convert -list compress); do convert -compress $a bilevel-image.png bilevel-image-$a.pdf; done[/color]

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

[code]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[/code]
/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.

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

I have a bunch of scanned monochrome images like this:

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

[code]convert input.tif -compress JBIG2 -density 300 output.pdf[/code]
Despite the much lower resolution, the resulting file is actually a little bit larger (and 16-bit):

[code]output.pdf PDF 764x1266 764x1266+0+0 16-bit Bilevel DirectClass 122KB 0.010u 0:00.010[/code]
What am I doing wrong?