# How to make this custom median for color images faster

**URL:** <https://discourse.julialang.org/t/how-to-make-this-custom-median-for-color-images-faster/104651>\
**Category:** Visualization\
**Tags:** question, images, juliaimages\
**Created:** [October 6, 2023, 9:21am UTC](https://discourse.julialang.org/t/how-to-make-this-custom-median-for-color-images-faster/104651 "2023-10-06T09:21:11Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rakesh](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rakesh/32/202257_2.png) [@Rakesh](https://discourse.julialang.org/u/Rakesh)\
**Post date:** [October 6, 2023, 9:21am UTC](https://discourse.julialang.org/t/how-to-make-this-custom-median-for-color-images-faster/104651/1 "2023-10-06T09:21:11Z")

</div>

I have made custom median filter for color images, but it performs slow and takes high memory compared to `OpenCV.medianBlur`. Here is code

```julia
using ImageIO
using FileIO
using ImageFiltering
using ImageCore
# using Statistics
using OpenCV
using BenchmarkTools

function median_filter(img, ksize::Tuple{Int64,Int64}=(3, 3))
    # mapwindow(median!, img, ksize)
    mapwindow(ImageFiltering.MapWindow.median_fast!, img, ksize)
end

function color_median_filter(img, ksize::Tuple{Int64,Int64}=(3, 3))
    cview_img = channelview(img)
    s::Tuple{Int64,Int64,Int64} = size(cview_img)
    filtered_image::Array{N0f8,3} = zeros(N0f8, s)
    for idx in 1:s[1]
        filtered_image[idx, :, :] = median_filter(cview_img[idx, :, :], ksize)
    end
    colorview(RGB, filtered_image)
end

noisy_img_path = "lighthouse_noisy.png"

lighthouse_noisy_cv = OpenCV.imread(noisy_img_path)
lighthouse_noisy = load(noisy_img_path)

s1 = 3
s2 = (3, 3)

```

```julia-repl
julia> @benchmark OpenCV.medianBlur($(lighthouse_noisy_cv), $(s1))
BenchmarkTools.Trial: 10000 samples with 1 evaluation.
 Range (min … max): 423.100 μs … 1.064 ms ┊ GC (min … max): 0.00% … 0.00%
 Time (median): 460.600 μs ┊ GC (median): 0.00%
 Time (mean ± σ): 476.162 μs ± 48.744 μs ┊ GC (mean ± σ): 0.00% ± 0.00%

       █▅▂▄▇▃
  ▁▂▃▃▆███████▅▄▄▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▂▁▁▂▁▁▁▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▂
  423 μs Histogram: frequency by time 663 μs <

 Memory estimate: 1.05 KiB, allocs estimate: 37.

julia> @benchmark color_median_filter($lighthouse_noisy, $s2)
BenchmarkTools.Trial: 41 samples with 1 evaluation.
 Range (min … max): 118.774 ms … 134.163 ms ┊ GC (min … max): 0.00% … 3.73%
 Time (median): 121.594 ms ┊ GC (median): 0.00%
 Time (mean ± σ): 122.864 ms ± 3.296 ms ┊ GC (mean ± σ): 0.94% ± 1.53%

      ▁ ▁█
  ▄▄▄▄█▄▄▁██▇▇▁▁▇▇▄▄▁▄▄▁▄▁▁▇▇▁▄▁▁▁▁▇▁▁▁▁▁▄▁▁▁▁▁▁▁▁▄▁▁▁▁▁▁▁▁▁▁▁▄ ▁
  119 ms Histogram: frequency by time 134 ms <

 Memory estimate: 12.37 MiB, allocs estimate: 107429.

```

* * *

Both filters remove noise from original image. Noisy image created using below code

```julia
using Noise
using TestImages
using Images

test_img = testimage("lighthouse")
save("lighthouse_noisy.png", salt_pepper(test_img))

```

### Julia version information

```julia-auto
Julia Version 1.9.3
Commit bed2cd540a (2023-08-24 14:43 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 16 × AMD Ryzen 7 PRO 5850U with Radeon Graphics
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-14.0.6 (ORCJIT, znver3)
  Threads: 1 on 16 virtual cores

```

Thanks

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<div class="post-metadata">

**Author:** ![juliohm](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/juliohm/32/215266_2.png) [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Post date:** [October 6, 2023, 9:30am UTC](https://discourse.julialang.org/t/how-to-make-this-custom-median-for-color-images-faster/104651/2 "2023-10-06T09:30:35Z")

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I believe there are packages with efficient median filters already. Try to search JuliaHub.

---

<div class="post-metadata">

**Author:** ![Rakesh](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rakesh/32/202257_2.png) [@Rakesh](https://discourse.julialang.org/u/Rakesh)\
**Post date:** [October 6, 2023, 3:47pm UTC](https://discourse.julialang.org/t/how-to-make-this-custom-median-for-color-images-faster/104651/3 "2023-10-06T15:47:00Z")

</div>

`@profview` show 62% spent in `partialsort!`

 ![canvas](https://global.discourse-cdn.com/julialang/original/3X/6/a/6aee782dd3ba43bb72b6d03b82846a5928c3d6b9.png)