Legacy ImageMagick Discussions Archive • convert from random input file to 1 bit bitmap

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convert from random input file to 1 bit bitmap

Posted: 2014-12-16T17:05:52-07:00

by Dannick

I want to be able to visualize the bit distribution in a file containing random bytes, like this

.

At the moment, I do it by converting the data file to ascii, and then to PBM (P1), and then convert it to a bitmap using ppmtobmp.

This is not a pretty way of doing it, but it works :/

How do I do this with convert? I do not know where to begin, since the input file is not an image but just a bunch of random bytes.

I tried "fooling" convert it was a an RGB file, eg: convert -depth 1 -monochrome -size 1920x1080.rgba output.bmp

This will give me a monochrome picture, but it is converted wrong, compared to the ppmtobmp way. It looks like it does not actually use 1 bit per pixel

Any starting pointers on how to do this?

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-16T17:28:03-07:00

by snibgo

IM can directly read and write P1 files, eg:

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f:\web\im>%IM%convert -size 10x10 gradient: -type bilevel -compress none x.pbm

f:\web\im>type x.pbm
P1
10 10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 0 0 1 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

"-compress none" means write ASCII text.

There is also a .gray format:

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f:\web\im>%IM%convert -size 100x100 gradient: -type bilevel -depth 1 x.gray

f:\web\im>%IM%convert -size 100x100 -depth 1 x.gray x.png

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-16T17:31:10-07:00

by Dannick

Thanks, but how do I do this without having to go via the pbm format?
I would like to do: convert [arguments] random.dat output.bmp

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-16T17:37:28-07:00

by snibgo

You'll have to experiment, as I can't see your file. Try:

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convert -size 1920x1080 -depth 1 GRAY:random.dat output.bmp

If that doesn't work, try:

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rename random.dat random.gray

convert -size 1920x1080 -depth 1 random.gray output.bmp

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-17T15:20:25-07:00

by Dannick

And experimenting I did! Thanks for the GRAY tip. This is how I got it perfected. Trial & error ftw...

Reference bmp (converted from pbm) :

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out1.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.009

Attempt 1:

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$ convert -size 1920x1080 -depth 1 GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 8-bit DirectClass 6.221MB 0.000u 0:00.009

Wrong depth in output bmp

Attempt 2:

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$ convert -size 1920x1080 -depth 1 -monochrome GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 8-bit DirectClass 6.221MB 0.000u 0:00.009

Still wrong depth

Attempt 3:

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$ convert -size 1920x1080 -depth 1 -monochrome -type bilevel GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 8-bit DirectClass 6.221MB 0.000u 0:00.000

And... still wrong depth

Attempt 4:

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$ convert -size 1920x1080 -depth 1 -monochrome -type bilevel -colors 2 GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.000

Finally! Now, perhaps I don't need all those options... Trimming:

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$ convert -size 1920x1080 -depth 1 -colors 2 GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.000

Great! But... the image is not identical to the reference one

At closer inspection, they look like inversed versions of each other. Ah... *one minute googling later since -inverse didn't work*
Attempt 5:

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$ convert -size 1920x1080 -depth 1 -colors 2 -negate GRAY:random.dat out2.bmp ; identify out2.bmp
out2.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.010

Now, the output bmp and the reference bitmap are seemingly identical. The files are not identical though - but that does not matter.

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out1.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.009
out2.bmp BMP 1920x1080 1920x1080+0+0 1-bit PseudoClass 2c 259KB 0.000u 0:00.010

snibgo, thanks for the rapid reply!

BTW, the random.dat is just any data. In this case it is output from /dev/urandom. To get data for a 1-bit 1920x1080 image, I just use dd:

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$ dd if=/dev/urandom bs=$((1920*1080/8)) count=1 of=random.dat

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-17T15:40:47-07:00

by Dannick

I just confirmed that the reference bmp and the convert:ed bmp are identical:

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$ convert out1.bmp out1.ppm ; convert out2.bmp out2.ppm ; md5sum out?.ppm
58a516ebdaf526423137a2b2a636ff7b  out1.ppm
58a516ebdaf526423137a2b2a636ff7b  out2.ppm

Hence, perfect conversion accomplished!

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-17T15:46:24-07:00

by snibgo

Good stuff. You can pipe dd directly into convert:

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dd if=/dev/urandom bs=$((1920*1080/8)) count=1 | convert -size 1920x1080 -depth 1 -negate GRAY:- -colors 2 out3.bmp

(I moved "-colors 2", because this operation should occur after convert reads the input, not before.)

IM contains its own noise generators, of course. See http://www.imagemagick.org/script/comma ... .php#noise

Re: convert from random input file to 1 bit bitmap

Posted: 2014-12-17T16:20:43-07:00

by Dannick

Yes, the IM noise generator I discovered earlier but for this operation I need a file containing the output from a known random source.

Thanks for the tip though, and very much thanks again for the GRAY tip which I've managed to miss during my IM knowledge hunt.