[R] [help] reduce the bit depth of a png file

Vera Thiemig vera.thiemig at ext.jrc.ec.europa.eu
Wed Jan 21 15:28:09 CET 2015

Dear all,


I would like to reduce the bit depth of a png file from originally 24 to 8
(with the main intention to decrease the file size).


With the ordinary png(.) command it seems to be not possible. So, I created
first the png file and then re-wrote it with writePNG of the png package
(http://cran.r-project.org/web/packages/png/png.pdf) as it is written that:


"Currently writePNG only produces 8-bit, deflate-compressed, non-quantized,
non-interlaced images. Note in particular that readPNG can read 16-bit
channels but storing them back using writePNG will strip the 8 LSB
(irrelevant for display purposes but possibly relevant for use of PNG in
signalprocessing if the input is truly 16-bit wide)."


However, I end up with a 24-bit file again :(


Anybody has an idea of how to proceed?


Thank you,



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