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Paolo said...

The no brain answer would be to use some graphics editor to convert from RGB to Gray scale.
In Mac OS X you can use the preview application: save as > Quartz Filter > Gray Tone.
In R you can use the EBImage Bioconductor package to convert the color mode from Color to Grayscale in this way:
img= readImage("super_histograms.pdf")
colorMode(img) <- Grayscale
display(img)

You can find useful hints about creating overlapping histograms at the following links: http://stackoverflow.com/questions/3541713/how-to-plot-two-histograms-together-in-r http://stackoverflow.com/questions/5328452/overlaid-histograms-in-r-ggplot2-preferred

HIH

Sep 15, 2011, 3:42:35 PM

Posted to How to Superimpose Histograms