Improper `Normed` handling in the contrast GUI

[kimikage]

This is a little related to issue #308 and PR #309. The contrast GUI causes errors with the images using Normed, such as N0f8.

julia> using ImageView

julia> using ImageView.FixedPointNumbers

julia> VERSION
v"1.10.4"

julia> pkgversion(ImageView)
v"0.12.4"

julia> n0f8s = N0f8[0.2 0.8];

julia> imshow(n0f8s); # and then slide "slider_max" to the left

┌ Warning: Executing #14:
└ @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\signals.jl:122
ERROR: 0.2N0f8 is not within the span of 0.20000000298023224:0.002362204759609042:0.800000011920929
Stacktrace:
  [1] error(s::String)
    @ Base .\error.jl:35
  [2] setindex!(s::GtkObservables.Slider{Float32}, ::Tuple{StepRangeLen{Float64, Base.TwicePrecision{Float64}, Base.TwicePrecision{Float64}, Int64}, N0f8})
    @ GtkObservables C:\Users\username\.julia\packages\GtkObservables\gSI6s\src\widgets.jl:173
  [3] (::ImageView.var"#130#133"{Observables.Observable{CLim{N0f8}}, Dict{String, Any}, N0f8, DataType})(cmin::Float32, cmax::Float32)
    @ ImageView C:\Users\username\.julia\packages\ImageView\QLmQc\src\contrast_gui.jl:103
  [4] invokelatest(::Any, ::Any, ::Vararg{Any}; kwargs::@Kwargs{})
    @ Base .\essentials.jl:892
  [5] invokelatest(::Any, ::Any, ::Vararg{Any})
    @ Base .\essentials.jl:889
  [6] (::Observables.MapCallback)(value::Any)
    @ Observables C:\Users\username\.julia\packages\Observables\YdEbO\src\Observables.jl:436
  [7] #invokelatest#2
    @ .\essentials.jl:892 [inlined]
  [8] invokelatest
    @ .\essentials.jl:889 [inlined]
  [9] notify
    @ C:\Users\username\.julia\packages\Observables\YdEbO\src\Observables.jl:206 [inlined]
 [10] setindex!(observable::Observables.Observable, val::Any)
    @ Observables C:\Users\username\.julia\packages\Observables\YdEbO\src\Observables.jl:123
 [11] (::GtkObservables.var"#14#15"{Observables.Observable{Float32}})(w::Gtk4.GtkScaleLeaf)
    @ GtkObservables C:\Users\username\.julia\packages\GtkObservables\gSI6s\src\widgets.jl:155
 [12] (::Gtk4.GLib.var"#134#136"{Ptr{Gtk4.GLib.GValue}, UInt32, Ptr{Gtk4.GLib.GValue}, Vector{Any}, GtkObservables.var"#14#15"{Observables.Observable{Float32}}})()
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\signals.jl:63
 [13] g_siginterruptible(f::Gtk4.GLib.var"#134#136"{Ptr{Gtk4.GLib.GValue}, UInt32, Ptr{Gtk4.GLib.GValue}, Vector{Any}, GtkObservables.var"#14#15"{Observables.Observable{Float32}}}, cb::Any)
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\signals.jl:244
 [14] GClosureMarshal(closuref::Ptr{Nothing}, return_value::Ptr{Gtk4.GLib.GValue}, n_param_values::UInt32, param_values::Ptr{Gtk4.GLib.GValue}, invocation_hint::Ptr{Nothing}, marshal_data::Ptr{Nothing})
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\signals.jl:57
 [15] (::Gtk4.GLib.var"#233#234")()
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\loop.jl:83
 [16] g_sigatom(f::Any)
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\signals.jl:211
 [17] glib_main()
    @ Gtk4.GLib C:\Users\username\.julia\packages\Gtk4\pLBGK\src\GLib\loop.jl:80

[kimikage]

This may be directly due to the fact that the slider range is based on Float64 while the slider value can be Normed. This should be solved by converting the values to float.

https://github.com/JuliaImages/ImageView.jl/blob/27fb1926c86cfda6ac84f86f34f0b88195156a37/src/contrast_gui.jl#L101

https://github.com/JuliaImages/ImageView.jl/blob/27fb1926c86cfda6ac84f86f34f0b88195156a37/src/contrast_gui.jl#L115-L116

cc: @jwahlstrand

[jwahlstrand]

Thanks, your suggestion does prevent the error! I'll submit a PR (unless you'd like to?)

[kimikage]

I do not have merge privileges on this repository, so I would like to ask you to make a PR.