# Images and the new color representation

**URL:** <https://discourse.julialang.org/t/images-and-the-new-color-representation/4793>\
**Category:** General Usage\
**Tags:** question, images\
**Created:** [July 11, 2017, 5:20pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793 "2017-07-11T17:20:04Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![harven](https://avatars.discourse-cdn.com/v4/letter/h/3da27b/32.png) [@harven](https://discourse.julialang.org/u/harven)\
**Post date:** [July 11, 2017, 5:20pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/1 "2017-07-11T17:20:04Z")

</div>

I can see that there are quite a few changes concerning Images.

I have a two dimensional array with triples of UInt8 as entries. How do I make it work with ImageView.imshow?  
As far as I understand, I must convert the UInt8 to the new type N0f8, but this does not seem to work.

```
julia> n0f8(UInt8(222))
ERROR: ArgumentError: FixedPointNumbers.Normed{UInt8,8} is an 8-bit type representing 256 values from 0.0 to 1.0; cannot represent 222

```

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**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [July 11, 2017, 8:18pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/2 "2017-07-11T20:18:39Z")

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If you want to just interpret a UInt8 (with a value from 0 to 255) as a `N0f8` (with a value from 0 to 1), then Julia’s built-in `reinterpret` will do what you want:

```julia
julia> reinterpret(N0f8, UInt8(222))
0.871N0f8

julia> reinterpret(N0f8, [UInt8(222), UInt8(0), UInt8(255)])
3-element Array{FixedPointNumbers.Normed{UInt8,8},1}:
 0.871N0f8
 0.0N0f8  
 1.0N0f8  

```

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<div class="post-metadata">

**Author:** ![harven](https://avatars.discourse-cdn.com/v4/letter/h/3da27b/32.png) [@harven](https://discourse.julialang.org/u/harven)\
**Post date:** [July 11, 2017, 9:15pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/3 "2017-07-11T21:15:49Z")

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Perfect!

Why does it fail on tuples? The error message is cryptic.

```
julia> reinterpret(N0f8, (0xde, 0x00, 0x0c))
ERROR: bitcast: target type not a leaf primitive type
Stacktrace:
 [1] reinterpret(::Type{FixedPointNumbers.Normed{UInt8,8}}, ::Tuple{UInt8,UInt8,UInt8}) at ./essentials.jl:155

```

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<div class="post-metadata">

**Author:** ![avik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/avik/32/17_2.png) [@avik](https://discourse.julialang.org/u/avik)\
**Post date:** [July 11, 2017, 9:19pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/4 "2017-07-11T21:19:25Z")

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> [@harven](#):
>
> Why does it fail on tuples?

because `reinterpret` does not have a method for tuples, only scalars and arrays. However, Julia’s dot broadcasting can automatically apply it to any collection

```julia
julia> reinterpret.(N0f8, (0xde, 0x00, 0x0c))
(0.871N0f8, 0.0N0f8, 0.047N0f8)

```

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<div class="post-metadata">

**Author:** ![Evizero](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/evizero/32/10118_2.png) [@Evizero](https://discourse.julialang.org/u/Evizero)\
**Post date:** [July 12, 2017, 11:42am UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/5 "2017-07-12T11:42:57Z")

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```julia
julia> A = [(0xff, 0x11, 0x33) (0x22, 0xff, 0xaa); (0x00, 0xff, 0x00) (0x00, 0x00, 0xff)]
2×2 Array{Tuple{UInt8,UInt8,UInt8},2}:
 (0xff, 0x11, 0x33) (0x22, 0xff, 0xaa)
 (0x00, 0xff, 0x00) (0x00, 0x00, 0xff)

julia> B = reinterpret(UInt8, A, (3,2,2))
3×2×2 Array{UInt8,3}:
[:, :, 1] =
 0xff 0x00
 0x11 0xff
 0x33 0x00

[:, :, 2] =
 0x22 0x00
 0xff 0x00
 0xaa 0xff

julia> C = normedview(N0f8, B)
3×2×2 Array{N0f8,3}:
[:, :, 1] =
 1.0N0f8 0.0N0f8
 0.067N0f8 1.0N0f8
 0.2N0f8 0.0N0f8

[:, :, 2] =
 0.133N0f8 0.0N0f8
 1.0N0f8 0.0N0f8
 0.667N0f8 1.0N0f8

julia> D = colorview(RGB, C)
2×2 Array{RGB{N0f8},2}:
 RGB{N0f8}(1.0,0.067,0.2) RGB{N0f8}(0.133,1.0,0.667)
 RGB{N0f8}(0.0,1.0,0.0) RGB{N0f8}(0.0,0.0,1.0)

```

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<div class="post-metadata">

**Author:** ![harven](https://avatars.discourse-cdn.com/v4/letter/h/3da27b/32.png) [@harven](https://discourse.julialang.org/u/harven)\
**Post date:** [July 13, 2017, 12:14pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/6 "2017-07-13T12:14:12Z")

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Thanks for all the answers. This was as simple as

`reinterpret(RGB{N0f8}, A)`

where `A` is the array of UInt8 triples.

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**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [July 13, 2017, 1:06pm UTC](https://discourse.julialang.org/t/images-and-the-new-color-representation/4793/7 "2017-07-13T13:06:25Z")

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Assuming you’re `using Images` (or at least `ImageCore`), a more generic solution is `colorview(RGB, normedview(A))`. You can only call `reinterpret` on `Array`s (though anything with dense storage would be implementable), whereas `colorview` works for any `AbstractArray`. `colorview` will call `reinterpret` when it’s applicable, and create a special wrapper type when not.

More detail at [Home · JuliaImages](http://juliaimages.github.io/latest/).