specialize imrotate for 0, 90, 180, 270 degrees by johnnychen94 · Pull Request #79 · JuliaImages/ImageTransformations.jl

johnnychen94 · 2019-12-14T12:41:12Z

img = testimage("cameraman") # (512, 512)

# Before: (514, 514)
# After: (512, 512)
size(imrotate(img, pi/2))

# Before: sizes are not equal
# After: true
imrotate(imrotate(imrotate(imrotate(img, pi/2), pi/2), pi/2), pi/2) == img

# Before: sizes are not equal
# After: true
imrotate(imrotate(img, pi), pi) == img

codecov · 2019-12-14T13:59:57Z

Codecov Report

Merging #79 into master will increase coverage by 0.56%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #79      +/-   ##
==========================================
+ Coverage   88.56%   89.12%   +0.56%     
==========================================
  Files           7        7              
  Lines         271      285      +14     
==========================================
+ Hits          240      254      +14     
  Misses         31       31

Impacted Files	Coverage Δ
src/warp.jl	`100% <100%> (ø)`	⬆️

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johnnychen94 · 2019-12-16T10:02:50Z

I believe this PR is ready for review and merge

Evizero · 2019-12-16T10:41:24Z

is it type stable? was it before this PR?

timholy

This looks good except for concerns about non-inferrability. I suppose an alternative would be to write specialized functions (rotate90, rotate180, rotate270) for specific rotations.

timholy · 2019-12-18T16:04:43Z

test/warp.jl

                @test_nowarn imrotate(img, π/4, axes(img))
                @test_nowarn imrotate(img, π/4, axes(img), Constant())
-                @test isequal(channelview(imrotate(img,π/4)), channelview(imrotate(img, π/4, Linear()))) # TODO: if we remove channelview the test will break for Float
+                @test isequal(channelview(imrotate(img, π/4)), channelview(imrotate(img, π/4, Linear()))) # NaN != NaN


The meaning of this comment is unclear. Do you mean that you wanted to write == but instead have to use isequal?

johnnychen94 · 2019-12-18T21:35:28Z

Thanks for the comment, I'm already aware of the type stability issue, I'll come back and try to fix that later when I finished the upgrading of Augmentor.jl made by @Evizero (for my own research interest)

kimikage · 2019-12-20T22:44:45Z

BTW, 360 ° seems to be missing.

kimikage · 2019-12-20T23:09:31Z

src/warp.jl

+    # 2. typemax(Int16) is 32767, we choose 32760 to make sure the
+    # discretization result of pi/2 is exactly pi/2 (or 90°)
+    max_num_angles = 32760


Although the same goes for the current code, why don't you use 32768?

Well... It's like I randomly chose the first number I found that meets the requirement, and I feel this choice doesn't matter for image processing tasks.

kimikage · 2019-12-20T23:19:10Z

src/warp.jl

+    θ = round(Int, 180*floor(mod(θ, 2pi)/pi*max_num_angles)/max_num_angles)
+    tform = recenter(RotMatrix{2}(θ/180*pi), center(img))


Don't use the θ! 😱

mileslucas · 2020-03-14T05:48:34Z

src/warp.jl

+    elseif θ == 90
+        idx = StepRange.(axes(img))
+        perm_img = PermutedDimsArray(img, (2, 1))
+        return view(perm_img, idx[2], reverse(idx[1]))
+    elseif θ == 180
+        idx = map(i->1:1:length(i), axes(img))
+        return view(img, reverse(idx[1]), reverse(idx[2]))
+    elseif θ == 270
+        idx = StepRange.(axes(img))
+        perm_img = PermutedDimsArray(img, (2, 1))
+        return view(perm_img, reverse(idx[2]), idx[1])


any reason to not use some of the tools in base?

https://docs.julialang.org/en/v1/base/arrays/#Base.rot180
https://docs.julialang.org/en/v1/base/arrays/#Base.rotl90
https://docs.julialang.org/en/v1/base/arrays/#Base.rotr90

I don't think @johnnychen94 want to reallocate the memory and relocate the elements.:smile:

True, and there won't be type stability issues if we collect them and return an Array; but that would be slower than views.

I don't have a good fix in mind for this at the moment.

kimikage · 2020-03-14T06:31:50Z

BTW, I think it is better to round the rotation matrix instead of quantizing the angle.

johnnychen94 · 2020-03-14T06:33:30Z

That sounds promising to me!

mkitti · 2020-12-21T11:12:47Z

It seems a bit dangerous to specialize on an approximation for an irrational number. Maybe it would be better to have a degree based version of imrotate and specialize on multiples of 90 like the title suggests? The discretized imrotate could then map to that.

Otherwise, I would really appreciate something like this. It's absence was duly noted when attempting something AoC2020 Day 20: https://adventofcode.com/2020/day/20

mkitti · 2020-12-25T17:14:30Z

sinpi and cospi could also have some relevance here.
https://docs.julialang.org/en/v1/base/math/#Base.Math.sinpi

timholy · 2021-10-10T19:08:09Z

I'll let @johnnychen94 decide what to do here, but I put all the tests from this PR into #149 and they pass.

crop images for special rotation degrees

7badcac

do not use warp for these special degress

f208d6b

johnnychen94 changed the title ~~crop images for special rotation degrees~~ specialize imrotate for 0, 90, 180, 270 degrees Dec 16, 2019

johnnychen94 added 2 commits December 16, 2019 17:59

add one more test case

dd3b7e2

ImageTransformations v0.8.1

ca777ff

timholy reviewed Dec 18, 2019

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kimikage reviewed Dec 20, 2019

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mileslucas reviewed Mar 14, 2020

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johnnychen94 mentioned this pull request Sep 8, 2021

imrotate(img, pi/2) changes size of image #145

Closed

timholy mentioned this pull request Oct 10, 2021

Fix imrotate for Irrational θ #149

Merged

timholy added a commit that referenced this pull request Oct 10, 2021

add more tests from #79

4c7b7c2

		θ = round(Int, 180floor(mod(θ, 2pi)/pimax_num_angles)/max_num_angles)
		tform = recenter(RotMatrix{2}(θ/180*pi), center(img))

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