[R] [FORGED] How to alpha entire plot?

[Paul Murrell]

Hi

Here is one way to do it ...

col1 <- "red"
col2 <- "blue"
EU <- data.frame(EuStockMarkets)
with(EU, plot(DAX, CAC, col=col2, type="h", ylim=c(0,6000)))
par(new=TRUE)
with(EU, plot(DAX, FTSE, col=col1, type="h", ylim=c(0,6000)))

## Convert 'graphics' to 'grid'
library(gridGraphics)
grid.echo()
## grid.ls(print=grobPathListing, viewports=TRUE)

## Rasterize spikes
library(rasterize)
downViewport("graphics-window-1-1")
grid.rasterize("graphics-plot-1-spike-1")
upViewport(0)
downViewport("graphics-window-2-1")
grid.rasterize("graphics-plot-2-spike-1")
upViewport(0)

## Apply alpha adjustment to rasterized spikes
spike1 <- as.matrix(grid.get("graphics-plot-1-spike-1")$raster)
alphaSpike1 <- adjustcolor(spike1, alpha=.3)
dim(alphaSpike1) <- dim(spike1)
grid.edit("graphics-plot-1-spike-1", raster=as.raster(alphaSpike1))
spike2 <- as.matrix(grid.get("graphics-plot-2-spike-1")$raster)
alphaSpike2 <- adjustcolor(spike2, alpha=.3)
dim(alphaSpike2) <- dim(spike2)
grid.edit("graphics-plot-2-spike-1", raster=as.raster(alphaSpike2))

... though that may not be the best way and may just reflect what I have 
been thinking about recently ...

https://www.stat.auckland.ac.nz/~paul/Reports/rasterize/rasterize.html

Paul


On 01/06/18 08:56, Ed Siefker wrote:
> I have two chromatograms I want plotted on the same axes.
> I would like the plots to be transparent, so the first chart is
> not obscured.
> 
> I have tried adjustcolor(..., alpha.f=0.3), the problem is that
> my chromatogram is so dense with datapoints that they
> overlap and the entire graph just ends up a solid color.  The
> second histogram still obscures the first.
> 
> Consider this example:
> 
> 
> col1 <- adjustcolor("red", alpha.f=0.3)
> col2 <- adjustcolor("blue", alpha.f=0.3)
> EU <- data.frame(EuStockMarkets)
> with(EU, plot(DAX, CAC, col=col2, type="h", ylim=c(0,6000)))
> par(new=TRUE)
> with(EU, plot(DAX, FTSE, col=col1, type="h", ylim=c(0,6000)))
> 
> The density of the red plot around 2000 completely obscures the blue
> plot behind it.
> 
> What I would like to do is plot both plots in solid colors, then alpha
> the entire thing, and then overlay them.  Or some other method that
> achieves a comparable result.
> Thanks
> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul using stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/