[R-sig-Geo] RGB in image()

[Michael Sumner]

I forgot about alpha, you'll need to modify the colours in ct to suit:

SGlogo <- readGDAL(logo)

cols <- SGDF2PCT(SGlogo)

cola <- rbind(col2rgb(cols$ct[170:200]), alpha = 150)

cols$ct[170:200] <- rgb(cola[1,], cola[2,], cola[3,], cola[4,],
maxColorValue = 255)
SGlogo$idx <- cols$idx
image(SGlogo, "idx", col=cols$ct)


Whether the transparency is supported will depend on the device, I
used windows().

Cheers, Mike.


On Sun, Dec 12, 2010 at 10:09 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> You need to generate an index on the grid and a colour table to use.
> See ?SGDF2PCT in the rgdal package, and the following should work:
>
>
>
>   cols <- SGDF2PCT(pd)
>     pd$idx <- cols$idx
>   image(pd, col = cols$ct)
>
> Also, this question is more appropriate for the R-Sig-Geo mailing list.
>
> Cheers, Mike.
>
> On Fri, Dec 10, 2010 at 9:20 PM,  <Tim.Haering at lwf.bayern.de> wrote:
>> Hello,
>>
>> I would like to plot a SpatialGridDataFrame using the image() function, but have problems with the colors. I want to create a transparent rgb image using three bands as red, green and blue and want to control the transparency with the alpha parameter.
>> I have a matrix "dist" containing my rgb values:
>>> head(dist)
>>          [,1]      [,2]      [,3]
>> [1,] 0.1895978 0.5196565 0.2907457
>> [2,] 0.2292516 0.5269284 0.2438200
>> [3,] 0.1514392 0.4990144 0.3495464
>> ...
>> ### create a color vector using rgb()
>>> cols <- apply(dist, 1, function(x) rgb(x[1], x[2], x[3], alpha = .2))
>>
>> ### rescale rgb values to c(0,255)
>>> red <- as.integer(RESCALE(dist[,1],0,255,min(dist[,1]), max(dist[,1])))
>>> green <- as.integer(RESCALE(dist[,2],0,255,min(dist[,2]), max(dist[,2])))
>>> blue <- as.integer(RESCALE(dist[,3],0,255,min(dist[,3]), max(dist[,3])))
>>
>> ### create a SGDF
>>> pd <- data.frame(RW = p$RW, HW = p$HW, red=red, green=green, blue=blue, cols)
>>> gridded(pd) = ~RW+HW
>>> pd <- as(pd, "SpatialGridDataFrame")
>>
>> ### using the red, green and blue parameters my image looks fine except that
>> ### my colors aren`t transparent
>>> image(pd, red="red", green="green", blue="blue")
>>
>> ### If I use my color vector (containing transparent colors) the image looks
>> ### speckled.
>>> image(pd, col = cols)
>>
>> Can somebody help me? Is there another way to make the color transparent?
>>
>> TIM
>>
>>
>> -------------------------------------
>> Tim Häring
>> Bavarian State Institute of Forestry
>> Department of Forest Ecology
>> Hans-Carl-von-Carlowitz-Platz 1
>> D-85354 Freising
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>
>
>
> --
> Michael Sumner
> Institute for Marine and Antarctic Studies, University of Tasmania
> Hobart, Australia
> e-mail: mdsumner at gmail.com
>



-- 
Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com