[R-SIG-Mac] How to generate 24-bit PNG on Mac OSX
Prof Brian Ripley
ripley at stats.ox.ac.uk
Thu Jul 31 08:23:31 CEST 2008
On Thu, 31 Jul 2008, Fán Lóng wrote:
> Hi there,
> When I am using the png() function as the following to generate a PNG
> file on Mac OSX Tiger, I found that the bit depth is 32. But I need
> 24 bit depth PNG. What should I do?
> To avoid using "cairo", and R-2.7.0 does not find a Xlib on my Mac, I
> also tried this one:
>> png(filename="/Users/usg/Desktop/new.png", type ="quartz" )
> It does not work, either.
> The manual says "png will use a palette if there are less than 256
> colours on the page, and record a 24-bit RGB file otherwise (or a
> 32-bit RGBA file if type = "cairo" and non-opaque colours are used)."
> I don't have to set the palette less than 256 colours, I just want a
> true color png file.
32-bit _is_ 'true color'. I think you need to turn anti-aliasing off if
you want only opaque colours.
In general though, if you make unreasonable requirements you need to be
prepared to do some work yourself -- there are many options to postprocess
32-bit PNG or palette PNG or PDF to other formats.
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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