# How to write a show function for an image-like type?

**URL:** <https://discourse.julialang.org/t/how-to-write-a-show-function-for-an-image-like-type/61583>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [May 21, 2021, 1:16pm UTC](https://discourse.julialang.org/t/how-to-write-a-show-function-for-an-image-like-type/61583 "2021-05-21T13:16:00Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![schrpe](https://avatars.discourse-cdn.com/v4/letter/s/f19dbf/32.png) [@schrpe](https://discourse.julialang.org/u/schrpe)\
**Post date:** [May 21, 2021, 1:16pm UTC](https://discourse.julialang.org/t/how-to-write-a-show-function-for-an-image-like-type/61583/1 "2021-05-21T13:16:00Z")

</div>

I’m developing a region module. A region is a subset of the discrete 2D cartesian plane. They can be used for very fast binary morphology and other things.

I’m trying to implement a show function, so that regions can be graphically displayed the same way as images can be displayed. My first attempt just creates an image (with binary content) and then shows the image.

```julia
using Images

"""
    Base.show(io, mime::MIME"image/png", r)

Shows a rich graphical display of a region. 
"""
function Base.show(io::IO, mime::MIME"image/png", r::Region)
    # convert region to an image and show image
    x0 = left(r)
    y0 = bottom(r)
    img = zeros(RGBA{N0f8}, height(r), width(r))
    for run in r.runs
        for column in run.columns
            img[run.row-y0+1, column-x0+1] = RGBA(0,0,1,0.5)
        end
    end
    Base.show(io, mime, img)
end

```

This forces me to use the Images module, which seems overkill to me. How could I write a show function with less severe dependencies on other modules?

I have been trying to find the source for the show function for images, but since I’m relatively new to Julia I was unable to find it.

Thanks and best regards  
schrpe

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<div class="post-metadata">

**Author:** ![MA\_Laforge](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ma_laforge/32/385_2.png) [@MA\_Laforge](https://discourse.julialang.org/u/MA_Laforge)\
**Post date:** [May 22, 2021, 6:04pm UTC](https://discourse.julialang.org/t/how-to-write-a-show-function-for-an-image-like-type/61583/2 "2021-05-22T18:04:12Z")

</div>

### `@edit` macro

In cases like this, you can use the `@edit` macro. All you do is add `@edit` in front of the command you are running, and Julia should open up the file housing the executed code.

In fact, if your editor supports jumping to a line number, Julia will even set your cursor to the exact line where the function definition is written.

_ **caveat:** _ You might have to to specify an editor using the `ENV[]` dictionnary if it isn’t already specified. For example:

```julia
ENV["EDITOR"]=raw"'C:\Program Files (x86)\Vim\vim81\gvim.exe'"

```

### Your specific problem

For your specific problem, you can just add `@edit` in front of the call to `Base.show()`:

```julia
@edit Base.show(io, mime, img)

```

On my version of Julia v1.6.1,` @edit` indicates that the code you are looking for is located in the `ImageShow.jl` package:

- `ImageShow/src/showmime.jl: line 23`

So that should be a good starting point to figuring out how to serialize your data as a PNG without using `ImageShow.jl`.

My guess is you’ll probably need to write a bit of header data before you write out the image data.

---

<div class="post-metadata">

**Author:** ![dpsanders](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dpsanders/32/3573_2.png) [@dpsanders](https://discourse.julialang.org/u/dpsanders)\
**Post date:** [May 22, 2021, 6:31pm UTC](https://discourse.julialang.org/t/how-to-write-a-show-function-for-an-image-like-type/61583/3 "2021-05-22T18:31:53Z")

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You could try using a plot recipe for the Plots.jl package.