JuliaImages / JuliaImages/ImageInTerminal.jl

imshow fails with Sixel backend: MethodError in sixel_encode

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Description

Hello! I got this error when trying the readme example. I'm using wezterm on linux, which has sixel support. Here is how to reproduce the error:

julia> using Pkg

julia> Pkg.status("ImageInTerminal")
No Matches in `~/.julia/environments/v1.12/Project.toml`

julia> Pkg.status("Sixel")
No Matches in `~/.julia/environments/v1.12/Project.toml`

julia> Pkg.add("ImageInTerminal")
   Resolving package versions...
   Installed ImageInTerminal ─ v0.5.4
    Updating `~/.julia/environments/v1.12/Project.toml`
  [d8c32880] + ImageInTerminal v0.5.4
    Updating `~/.julia/environments/v1.12/Manifest.toml`
  [a8cc5b0e] + Crayons v4.1.1
  [d8c32880] + ImageInTerminal v0.5.4
  [c8c2cc18] + XTermColors v0.2.1
Precompiling packages finished.
  1 dependency successfully precompiled in 2 seconds. 232 already precompiled.

julia> Pkg.add("Sixel")
   Resolving package versions...
   Installed Sixel ─ v0.1.5
    Updating `~/.julia/environments/v1.12/Project.toml`
  [45858cf5] + Sixel v0.1.5
    Manifest No packages added to or removed from `~/.julia/environments/v1.12/Manifest.toml`

julia> Pkg.status("ImageInTerminal")
Status `~/.julia/environments/v1.12/Project.toml`
  [d8c32880] ImageInTerminal v0.5.4

julia> Pkg.status("Sixel")
Status `~/.julia/environments/v1.12/Project.toml`
  [45858cf5] Sixel v0.1.5

julia> using TestImages

julia> testimage("mandril_color")
512×512 Matrix{ColorTypes.RGB{FixedPointNumbers.N0f8}}:
 RGB(0.651, 0.545, 0.243)  RGB(0.22, 0.188, 0.137)   …  RGB(0.671, 0.741, 0.443)
 RGB(0.416, 0.451, 0.196)  RGB(0.545, 0.392, 0.169)     RGB(0.459, 0.486, 0.224)
 RGB(0.294, 0.251, 0.125)  RGB(0.482, 0.42, 0.188)      RGB(0.38, 0.29, 0.157)
 RGB(0.227, 0.29, 0.176)   RGB(0.541, 0.518, 0.212)     RGB(0.196, 0.29, 0.165)
 RGB(0.384, 0.286, 0.165)  RGB(0.549, 0.482, 0.2)       RGB(0.282, 0.325, 0.157)
 RGB(0.286, 0.29, 0.125)   RGB(0.282, 0.294, 0.125)  …  RGB(0.671, 0.741, 0.451)
 RGB(0.153, 0.09, 0.09)    RGB(0.204, 0.153, 0.09)      RGB(0.612, 0.612, 0.471)
 RGB(0.153, 0.063, 0.094)  RGB(0.188, 0.169, 0.094)     RGB(0.553, 0.612, 0.294)
 RGB(0.192, 0.165, 0.196)  RGB(0.224, 0.129, 0.09)      RGB(0.459, 0.478, 0.227)
 RGB(0.169, 0.098, 0.09)   RGB(0.153, 0.063, 0.094)     RGB(0.537, 0.514, 0.224)
 RGB(0.09, 0.094, 0.071)   RGB(0.188, 0.161, 0.098)  …  RGB(0.286, 0.2, 0.11)
 RGB(0.161, 0.063, 0.086)  RGB(0.192, 0.157, 0.098)     RGB(0.196, 0.29, 0.165)
 ⋮                                                   ⋱
 RGB(0.486, 0.643, 0.541)  RGB(0.459, 0.58, 0.518)      RGB(0.349, 0.259, 0.196)
 RGB(0.447, 0.58, 0.514)   RGB(0.443, 0.541, 0.518)     RGB(0.251, 0.22, 0.263)
 RGB(0.349, 0.416, 0.486)  RGB(0.447, 0.482, 0.502)     RGB(0.29, 0.325, 0.322)
 RGB(0.388, 0.482, 0.42)   RGB(0.451, 0.514, 0.412)     RGB(0.255, 0.192, 0.192)
 RGB(0.349, 0.416, 0.478)  RGB(0.392, 0.478, 0.427)  …  RGB(0.294, 0.318, 0.318)
 RGB(0.388, 0.38, 0.384)   RGB(0.345, 0.412, 0.482)     RGB(0.255, 0.294, 0.263)
 RGB(0.322, 0.357, 0.29)   RGB(0.349, 0.416, 0.478)     RGB(0.286, 0.294, 0.251)
 RGB(0.353, 0.416, 0.478)  RGB(0.443, 0.514, 0.514)     RGB(0.294, 0.314, 0.329)
 RGB(0.455, 0.541, 0.631)  RGB(0.451, 0.58, 0.506)      RGB(0.29, 0.294, 0.224)
 RGB(0.451, 0.588, 0.667)  RGB(0.455, 0.537, 0.62)   …  RGB(0.251, 0.224, 0.251)
 RGB(0.451, 0.588, 0.667)  RGB(0.455, 0.537, 0.62)      RGB(0.251, 0.224, 0.251)

julia> using ImageInTerminal

julia> testimage("mandril_color")
Error showing value of type Matrix{ColorTypes.RGB{FixedPointNumbers.N0f8}}:

SYSTEM (REPL): showing an error caused an error
ERROR: 1-element ExceptionStack:
MethodError: no method matching sixel_write_callback_function(::Ptr{Int8}, ::Int32, ::IOContext{IOBuffer})
The function `sixel_write_callback_function` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  sixel_write_callback_function(::Ptr{Int8}, ::Int32, ::Ref{T}) where T<:IO
   @ Sixel ~/.julia/packages/Sixel/X78VX/src/backend/libsixel/encoder.jl:14

Stacktrace:
  [1] sixel_encode
    @ ~/.julia/packages/Sixel/X78VX/src/backend/libsixel/CModule.jl:286 [inlined]
  [2] (::Sixel.LibSixel.LibSixelEncoder)(io::IOContext{IOBuffer}, bytes::Matrix{ColorTypes.RGB{FixedPointNumbers.N0f8}})
    @ Sixel.LibSixel ~/.julia/packages/Sixel/X78VX/src/backend/libsixel/encoder.jl:34
  [3] sixel_encode(io::IOContext{…}, img::Matrix{…}, enc::Sixel.LibSixel.LibSixelEncoder; transpose::Bool, kwargs::@Kwargs{})
    @ Sixel ~/.julia/packages/Sixel/X78VX/src/encoder.jl:93
  [4] sixel_encode (repeats 2 times)
    @ ~/.julia/packages/Sixel/X78VX/src/encoder.jl:77 [inlined]
  [5] sixel_encode
    @ ~/.julia/packages/ImageInTerminal/U2jcL/src/ImageInTerminal.jl:131 [inlined]
  [6] imshow(io::IOContext{REPL.LimitIO{…}}, img::Matrix{ColorTypes.RGB{…}}, maxsize::Tuple{Int64, Int64}; kw::@Kwargs{})
    @ ImageInTerminal ~/.julia/packages/ImageInTerminal/U2jcL/src/ImageInTerminal.jl:115
  [7] imshow (repeats 2 times)
    @ ~/.julia/packages/ImageInTerminal/U2jcL/src/ImageInTerminal.jl:110 [inlined]
  [8] show(io::IOContext{REPL.LimitIO{…}}, mime::MIME{Symbol("text/plain")}, img::Matrix{ColorTypes.RGB{…}})
    @ ImageInTerminal ~/.julia/packages/ImageInTerminal/U2jcL/src/ImageInTerminal.jl:68
  [9] show_repl(io::IO, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:548
 [10] show_limited(io::IO, mime::MIME, x::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:517
 [11] (::REPL.var"#display##0#display##1"{REPL.REPLDisplay{…}, MIME{…}, Base.RefValue{…}})(io::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:540
 [12] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:833
 [13] display(d::REPL.REPLDisplay, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:526
 [14] display
    @ ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:546 [inlined]
 [15] display(x::Any)
    @ Base.Multimedia ./multimedia.jl:340
 [16] (::REPL.var"#print_response##2#print_response##3")()
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:590
 [17] repl_backend_loop(backend::REPL.REPLBackend, get_module::Function)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:445
 [18] start_repl_backend(backend::REPL.REPLBackend, consumer::Any; get_module::Function)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:427
 [19] start_repl_backend
    @ ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:424 [inlined]
 [20] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool, backend::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:653
 [21] run_repl(repl::REPL.AbstractREPL, consumer::Any)
    @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:639
 [22] run_std_repl(REPL::Module, quiet::Bool, banner::Symbol, history_file::Bool)
    @ Base ./client.jl:478
 [23] run_main_repl(interactive::Bool, quiet::Bool, banner::Symbol, history_file::Bool)
    @ Base ./client.jl:499
 [24] repl_main
    @ ./client.jl:586 [inlined]
 [25] _start()
    @ Base ./client.jl:561
Stacktrace:
 [1] print_response(errio::IO, response::Any, backend::Union{…}, show_value::Bool, have_color::Bool, specialdisplay::Union{…})
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:599
 [2] (::REPL.var"#print_response##0#print_response##1"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:558
 [3] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:833
 [4] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:556
 [5] (::REPL.var"#do_respond#73"{…})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:1192
 [6] run_interface(terminal::Base.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
   @ REPL.LineEdit ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/LineEdit.jl:2854
 [7] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:1663
 [8] (::REPL.var"#61#62"{REPL.LineEditREPL, REPL.REPLBackendRef})()
   @ REPL ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:650
Some type information was truncated. Use `show(err)` to see complete types.

julia> versioninfo()
Julia Version 1.12.4
Commit 01a2eadb047 (2026-01-06 16:56 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 24 × 12th Gen Intel(R) Core(TM) i7-12800HX
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, alderlake)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 24 virtual cores)

julia> using Sixel

julia> Sixel.is_sixel_supported()
true

julia> sixel_encode(testimage("mandril_color"))

I found that directly using sixel_encode renders the image, so it appears that using stdout is fine.
Image

When I check the source code of imshow, I noticed that it sends IOContext to sixel_encode, which appears to trigger the error.

function imshow(
    io::IO, img::AbstractArray{<:Colorant}, maxsize::Tuple=displaysize(io); kw...
)
    buf = IOContext(PipeBuffer(), :color => get(io, :color, false))
    if choose_sixel(img)
        sixel_encode(buf, img)
...

I changed this part of the code to

function imshow(
    io::IO, img::AbstractArray{<:Colorant}, maxsize::Tuple=displaysize(io); kw...
)
    inner_buf = PipeBuffer()
    buf = IOContext(inner_buf, :color => get(io, :color, false))
    if choose_sixel(img)
        sixel_encode(inner_buf, img)

Now it appears to work properly

Image

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with imshow and its sixel_encode call in src/ImageInTerminal.jl, then reproduce the README example with Julia 1.12 and Sixel enabled. Verify that displaying an image through imshow works in WezTerm without the reported MethodError, while direct sixel_encode behavior remains unchanged.

Written by the indexing model from the issue text.

Assessment

Tech stack
julia
Domain
cli
Issue type
Bug
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
65/100

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