Incorrectly export GIF image

[RexWzh]

By save("xxx.gif", bitmat), one should get a white picture, however, the output is black.

using FileIO
save("one.gif", ones(Bool, 200, 200)) # get a black image
load("one.gif") |> iszero # true

More generally, when the rate of zeros is small enough, the ones-matrix is treated as a zeros-matrix.

a = ones(Bool, 200, 200)
# set zero on a small range
ind = rand(1:40000, 300)
a[ind] .= false
save("small.gif", a) 
load("small.gif") |> iszero # true again
# set zero on more place
ind = rand(1:40000, 3000)
a[ind] .= false
save("normal.gif", a) # now we get the right image

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This issue occurs only in the case of gif, might have to do with the wrapper of ImageMagick.jl?