How to load a png image as an array in Julia?-CodePudding

How can I load a png as an array using Julia? I have a 256X256 image and I would like to load it as a 256X256 float array.

I tried using Images

using Images

img = load("pic.png")

however this merely loads and plots the image and I am not able to extract pixel values.

Additionally, I have tried

img = read("pic.png")

but this loads all the values into a vector. In theory I can reshape the vector to make it 256X256, but I was hoping for something that could work without me having to know the shape of the image ahead of time.

Lastly, if I load PyPlot I can load the image exactly how I want

import PyPlot as plt

img = plt.imread("pic.png")

however I would ideally like to be able to load the image with without invoking PyCall and.

CodePudding user response：

The recommended approach is to use FileIO. FileIO will choose appropiate parser (could be ImageMagick but for png it will be raher PNGFiles.jl instead). This provides you a common central interface for accessing images.

Note that this approach is also recommended on the ImageMagick.jl GitHub page

julia> using FileIO

julia> img = FileIO.load("c:\\temp\\fig.png")
288×432 Array{RGBA{N0f8},2} with eltype ColorTypes.RGBA{FixedPointNumbers.N0f8}:
 RGBA{N0f8}(1.0,1.0,1.0,0.0)  …  RGBA{N0f8}(1.0,1.0,1.0,0.0)
 RGBA{N0f8}(1.0,1.0,1.0,0.0)     RGBA{N0f8}(1.0,1.0,1.0,0.0)
 ⋮                            ⋱
 RGBA{N0f8}(1.0,1.0,1.0,0.0)  …  RGBA{N0f8}(1.0,1.0,1.0,0.0)
 RGBA{N0f8}(1.0,1.0,1.0,0.0)     RGBA{N0f8}(1.0,1.0,1.0,0.0)

If you want this as a 3 dimensional Array you need to be using Images and try channelview:

julia> imgarr = channelview(img)
4×288×432 reinterpret(reshape, N0f8, ::Array{RGBA{N0f8},2}) with eltype N0f8:
[:, :, 1] =
 1.0  1.0  1.0  1.0  1.0  1.0  …  1.0  1.0  1.0  1.0  1.0
 1.0  1.0  1.0  1.0  1.0  1.0     1.0  1.0  1.0  1.0  1.0
...

If you want a different order of dimensions this can be further combined with permutedims(imgarr, [2,3,1])