Using the data storage type defined on this page for raster images, read an image from a PPM file (binary P6 prefered).
(Read the definition of PPM file on Wikipedia.)

Task: Use write ppm file solution and grayscale image solution with this one in order to convert a color image to grayscale one.

using Images, FileIO, Netpbm
 
rgbimg = load("data/bitmapInputTest.ppm")
greyimg = Gray.(rgbimg)
save("data/bitmapOutputTest.ppm", greyimg)