Turn PDF into grayscale
Dariusz J. Garbowski
thuforuk at yahoo.co.uk
Tue Jun 27 00:08:00 BST 2006
On 06/26/2006 11:11 PM, Sundar Nagarajan wrote:
> Pupeno wrote:
>> I have some color PDFs I'd like to turn into grayscale, any ideas how ?
>> I have tried printing to PDF (the pdf itself) and setting it to
>> grayscale, but the PDF ends up in color anyway.
>> Thank you.
> You can do this quite simply at the command line using the Imagemagick
> tools. Install imagemagick ('apt-get install imagemagick' should do the
> to convert a file named color.pdf to grayscale and store the output in a
> file named gray.pdf:
> convert -colorspace GRAY color.pdf gray.pdf
> The only drawback I see is that this always seems to choose a gray
> colorspace with 256 colors (while the original colorspace may have
> (e.g.) 64K colors. Maybe someone else can comment whether the GRAY
> colorspace is always 8-bit.
This is simple: gray colour is made of all three RGB channels having the
same value. Thus you have:
R G B shade of gray
0 0 0 black
1 1 1 almost black
2 2 2 almost black
127 127 127 gray
128 128 128 a bit lighter gray
255 255 255 white
what makes 256 colour space (or "gray space" ;-) This can only improve
if you have more bits-per-channel. Notice that 24 bit colour jpg is only
8 bit per channel (3 channels * 8 bit = 24 bit).
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