Concat and replace PNG transparent images.

concat.jl

# Concatenate images vertically and replace transparancy with white.
using Images

a = readdir(".")
pngs = filter(x->endswith(x,".png"),a)
imgsperpage = 4

pages = length(pngs) ÷ imgsperpage


function replaceTransp(x)
	if x == RGBA(0,0,0,0)
		return RGBA(1,1,1,1)
	else
		return x
	end
end


for i in 0:pages
   filenames = String[]
   for j in 1:imgsperpage
	   idx = i*imgsperpage+j
	   if idx <= length(pngs)
		println(idx)
		push!(filenames,pngs[idx])	
	   end
   end
   if length(filenames) != 0
	   page = vcat(tuple(map(x->load(x),filenames)...)...) 
	   p = i + 1 
	   #save(joinpath("output","$p.png"), page)
	   save(joinpath("output","$p.png"), map(replaceTransp,page))
   end
end