# Should we use N0f8 to store image?

**URL:** <https://discourse.julialang.org/t/should-we-use-n0f8-to-store-image/14315>\
**Category:** Visualization\
**Created:** [August 30, 2018, 1:00pm UTC](https://discourse.julialang.org/t/should-we-use-n0f8-to-store-image/14315 "2018-08-30T13:00:51Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![JohnnyChen94](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johnnychen94/32/29979_2.png) [@JohnnyChen94](https://discourse.julialang.org/u/JohnnyChen94)\
**Post date:** [August 30, 2018, 1:00pm UTC](https://discourse.julialang.org/t/should-we-use-n0f8-to-store-image/14315/1 "2018-08-30T13:00:51Z")

</div>

We use `N0f8` to store image data in default.

But I wonder if this does correctly.

```julia
using Images

# my custom function
function down_intensity!(img::Array{Gray{T}}, bit) where T
    gray_level = range(0, stop = 1, length= Int(2^ bit +1))
    inds = [gray_level[i] .< img .<= gray_level[i+1] 
        for i in 1:length(gray_level)-1]
    
    # This for-loop is slow
    for i in 1:length(gray_level)-1
        img[inds[i]] = fill(gray_level[i],length(findall(inds[i])))
    end
    img = Gray{T}.(img/maximum(img))
    return img
end
function down_intensity(img::Array{Gray{T}}, bit) where T
    dest_img = copy(img)
    down_intensity!(dest_img, bit)
end

graybar = Gray{Float32}.(transpose(repeat(range(0,stop=1,length=512),1,50)))

bits = 4:-1:1
imgs_builtin = [Gray{N0f8}.(Gray{Normed{UInt8, bit}}.(graybar)) for bit in bits]
imgs_custom = [down_intensity(graybar, bit) for bit in bits]

img_diffs = colorview(Gray,hcat(vcat(imgs_builtin...),vcat(imgs_custom...)))

```

The left column shows results of the builtin way, the right column shows that of my way. As you can see, the left column is not spanned uniformly; there’s more on the center, less on both sides.

 ![Unknown](https://global.discourse-cdn.com/julialang/original/3X/f/3/f30115cfa37e1fbb0591fff0c7d7115c355c497b.png)

Update:

I find some note saying pixel at `i, j` is a sensor that _integrates_ the intensity over an area spanning `i±0.5, j±0.5` (this is a good model of how a camera pixel actually works). In this opinion, `N0f8` seems reasonable.