r - Function grid.raster returns NULL in R

Question

I've been trying to do some raster image manipulation in R language using grid package. The problem is that I cannot retrive a return value from grid.raster function. When I do:

result <- grid.raster(inputData)

instead of "a rastergrob grob" (as specified in a documentation) I receive a NULL object.

I've double checked it with an example from the documentation:

redGradient <- matrix(hcl(0, 80, seq(50, 80, 10)), nrow=4, ncol=5)
grid.newpage()
result <- grid.raster(redGradient)

Still result is just a NULL object. Is R doing some return value interception here? If so, how can I get it?

Answer 1

使用rasterGrob功能：

result <- rasterGrob(redGradient)

这两个函数共享一个文档页面，但是查看源代码，您可以看到grid.raster创建 grob 然后绘制它，返回grid.draw( NULL) 的值，而rasterGrob简单地返回 grob。