reduce image display time/memory for Juno and IJulia

[johnnychen94]

This is tested in a remote IJulia (100M LAN network), similar results can be observed from local Juno and IJulia. (this situation doesn't show in terminal REPL)

using TestImages
img = testimage("cameraman")
@time display(img)
@time display(img)
# 5.357775 seconds (9.10 M allocations: 544.977 MiB, 4.70% gc time)
# 2.960242 seconds (3.68 M allocations: 290.248 MiB, 11.38% gc time)

using TestImages, ImageShow
img = testimage("cameraman")
@time display(img)
@time display(img)
# 3.167470 seconds (8.06 M allocations: 404.792 MiB, 6.76% gc time)
# 0.128455 seconds (9.60 k allocations: 1.644 MiB)

Also, there's a significant network traffic if not using ImageShow (if using ImageShow the out traffic is at most 350Kb)

as a comparision,

# terminal REPL
using TestImages
img = testimage("cameraman")
@time display(img)
@time display(img)
# 0.616769 seconds (1.77 M allocations: 86.887 MiB, 3.71% gc time)
# 0.031414 seconds (72.89 k allocations: 2.940 MiB)

Any ideas what might cause this problem?

[timholy]

Try Juno.@profiler display(img). You'll see there's a lot of JSON serialization.

If there's anything to fix, it's certainly not here (maybe ImageShow.jl?). I'll transfer it there, but please close it if you don't think there's anything that needs fixing. (Unless there's a more concrete problem this causes, this seems low priority so I don't plan on poking at it further myself.)

[RalphAS]

I believe the extra traffic arises because the default image presentation from Juno/IJulia is via SVG. The main point of this package is to switch to PNG instead, which is much faster for showing dense images (locally or remotely). I presume there is a reason for the SVG default, but I have not seen it documented.

TestImages and similar packages depend on ImageCore and FileIO; the latter invokes ImageMagick or QuartzImageIO as needed.

It was a design decision to make ImageCore as lightweight as reasonably possible, and FileIO is just a shell, so neither of them should depend on ImageShow.

One option is to have ImageMagick and QuartzImageIO depend on ImageShow.

A fallback is to have a Requires.jl clause in ImageCore so that if Juno or IJulia is loaded, then ImageShow is imported too. Unfortunately Pkg doesn't fully understand Requires, so that might generate annoying messages.

[johnnychen94]

@kimikage can we close this issue?

[kimikage]

If you are satisfied with the measures in Colors.jl, you can.