Error writing png with color mode 0 and 1-bit depth in ruby 2.0.0

[nielsgl]

I found a problem with writing pngs with color mode 0 and 1-bit depth when using ruby 2.0.0p247. The error does not occur with ruby versions < 2. This is an example of how to reproduce it:

appel:code niels$ ruby --version
ruby 1.9.3p448 (2013-06-27 revision 41675) [x86_64-darwin12.5.0]
appel:code niels$ irb -r qrencoder
irb(main):001:0> qrcode = QREncoder.encode("Hello world!")
=> #<QREncoder::QRCode:0x007fd1a98417a0>
irb(main):002:0> qrcode.save_png("/tmp/helloqr.png")
=> #<File:/tmp/helloqr.png (closed)>
irb(main):003:0> exit
appel:code niels$ rbenv local 2.0.0-p247 
appel:code niels$ rbenv rehash
appel:code niels$ ruby --version
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.5.0]
appel:code niels$ irb -r qrencoder
irb(main):001:0> qrcode = QREncoder.encode("Hello world!")
=> #<QREncoder::QRCode:0x007fcf43825d10>
irb(main):002:0> qrcode.save_png("/tmp/helloqr2.png")
ChunkyPNG::NotSupported: No encoder found for color mode 0 and 1-bit depth!
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:370:in `encode_png_pixels_to_scanline_method'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:210:in `encode_png_image_pass_to_stream'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:174:in `encode_png_image_without_interlacing'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:161:in `encode_png_pixelstream'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:85:in `to_datastream'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/image.rb:62:in `to_datastream'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:35:in `write'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:43:in `block in save'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:43:in `open'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/chunky_png-1.2.5/lib/chunky_png/canvas/png_encoding.rb:43:in `save'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/qrencoder-1.4.1/lib/qrencoder/png.rb:27:in `method_missing'
    from /Users/niels/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/qrencoder-1.4.1/lib/qrencoder/qrcode.rb:11:in `save_png'
    from (irb):2
    from /Users/niels/.rbenv/versions/2.0.0-p247/bin/irb:12:in `<main>'
irb(main):003:0> 

[wvanbergen]

This is weird. The test suite, with includes an example using this mode, works fine for me on ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.3.0]

I am suspecting a weird interaction issue with the QR code library you're using. Can you figure out what the exact arguments are (including type) that chunky_png is called with from that library?

[nielsgl]

So the library generates a qrcode and then wraps it in a png, with a bunch of points like:

[
  [0] [
    [0] 0,
    [1] 0
  ],
  [1] [
    [0] 1,
    [1] 0
  ], ...
]

with a margin of 4, pixels_per_module = 1, background = 4294967295, width = 29, and a canvas is a < ChunkyPNG::Image 29x29 [ [#ffffff #ffffff .... ] ... ]
and then it calls png.save(path), where path is a string.

[wvanbergen]

The exact example you pasted works fine for me:

~/  $ ruby -v
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]
~/ $ irb
irb(main):001:0> require 'qrencoder'
=> true
irb(main):002:0> qrcode = QREncoder.encode("Hello world!")
=> #<QREncoder::QRCode:0x007f91fa1dd3a8>
irb(main):003:0> qrcode.save_png("/tmp/helloqr2.png")
=> #<File:/tmp/helloqr2.png (closed)>

I am using qrencoder version 1.4.1