[Rd] readPNG gives warnings and doesn't execute sample code from help files

[Joris Meys]

I believed the standard plotting device on R in 2.12.1 would support
per-pixel alpha. It does support alpha, as

 plot(1:2,type="l")
 polygon(c(1,1,2,2),c(1,2,2,1),col=rgb(60,100,60,60,maxColorValue=255))

plots correctly. Which device should I use then?

Cheers
Joris

On Mon, Feb 14, 2011 at 5:30 PM, Simon Urbanek
<Simon.Urbanek at r-project.org> wrote:
> Joris,
>
> On Feb 14, 2011, at 10:05 AM, Joris Meys wrote:
>
>> Dear all,
>>
>> I noticed in the latest R version (R.2.12.1) that the readPNG gives
>> following warning when running the example code in the help file (or
>> when using any other png for that matter) :
>>
>> 50: In rasterImage(img, 1.2, 1.27, 1.8, 1.73) :
>>  Per-pixel alpha not supported on this device
>>
>> No picture is shown, and code I used to be able to run, doesn't run any more.
>>
>
> You may want to use a device that supports alpha. The R logo in the example uses alpha so are probably the images you are using. If you don't want to (or can't) use a device that supports alpha, you'll have to flatten the alpha, - i.e. plot just img[,,1:3]
> However, most images don't have color where alpha is zero, so you'll have to replace it with the background color, e.g.:
> r = as.raster(img[,,1:3])
> r[img[,,4] == 0] = "white"
>
> Cheers,
> Simon
>
>
>
>>> sessionInfo()
>> R version 2.12.1 (2010-12-16)
>> Platform: i386-pc-mingw32/i386 (32-bit)
>>
>> locale:
>> [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United
>> States.1252    LC_MONETARY=English_United States.1252
>> [4] LC_NUMERIC=C                           LC_TIME=English_United
>> States.1252
>>
>> attached base packages:
>> [1] grDevices datasets  splines   graphics  stats     tcltk     utils
>>   methods   base
>>
>> other attached packages:
>> [1] png_0.1-2       svSocket_0.9-51 TinnR_1.0.3     R2HTML_2.2
>> Hmisc_3.8-3     survival_2.36-2
>>
>> loaded via a namespace (and not attached):
>> [1] cluster_1.13.2  grid_2.12.1     lattice_0.19-13 svMisc_0.9-61
>> tools_2.12.1
>>
>>
>> --
>> Joris Meys
>> Statistical consultant
>>
>> Ghent University
>> Faculty of Bioscience Engineering
>> Department of Applied mathematics, biometrics and process control
>>
>> tel : +32 9 264 59 87
>> Joris.Meys at Ugent.be
>> -------------------------------
>> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
>>
>>
>
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php