No plot with ggRGB(rlogo, ggLayer = TRUE)

[aloboa]

Considering

wave <- data.frame(x = c(0, 0:100,100), y = c(0,sin(seq(0,2*pi,pi/50))*10+20, 0))
ggplot(data=wave, aes(x, y)) + 
    ggRGB(rlogo, ggLayer = TRUE) + 
    geom_polygon(alpha=0.2) +
    coord_equal(ylim=c(0,75))

why is the following producing an empty plot?

ggplot() + 
    ggRGB(rlogo, ggLayer = TRUE) + 
    coord_equal()