Image rotation

Hi All,

I can’t find an analog for Matlab “imrotate” function.
Maybe I overlooked it, or really there isn’t such thing?

Here it is in Matlab, to save you clicking:

imrotate Rotate image.
    B = imrotate(A,ANGLE) rotates image A by ANGLE degrees in a
    counterclockwise direction around its center point. To rotate the image
    clockwise, specify a negative value for ANGLE. imrotate makes the output
    image B large enough to contain the entire rotated image. imrotate uses
    nearest neighbor interpolation, setting the values of pixels in B that
    are outside the rotated image to 0 (zero).
    B = imrotate(A,ANGLE,METHOD) rotates image A, using the interpolation
    method specified by METHOD. METHOD is a string that can have one of the
    following values. The default value is enclosed in braces ({}).
         {'nearest'}  Nearest neighbor interpolation
         'bilinear'   Bilinear interpolation
         'bicubic'    Bicubic interpolation. Note: This interpolation
                      method can produce pixel values outside the original
    B = imrotate(A,ANGLE,METHOD,BBOX) rotates image A, where BBOX specifies
    the size of the output image B. BBOX is a text string that can have
    either of the following values. The default value is enclosed in braces
         {'loose'}    Make output image B large enough to contain the
                      entire rotated image. B is generally larger than A.
         'crop'       Make output image B the same size as the input image
                      A, cropping the rotated image to fit.

Use warp from ImageTransformations. But I see it’s missing a docstring…I’ll fix that and publish a new version today.

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great thank you, I’ll try.

some unrelated stuff - translating from Matlab, I struggle with couple of syntactic trivia.
First is thresholding, like here in Matlab:

>> x = [ 1 3 78 98 11];
>> y=x>60

y =

  1×5 logical array

   0   0   1   1   0

another one, how to initiate array by NaNs.

> NaN(10)
x MethodError: objects of type Float64 are not callable

certainly can write local functions, but that’s clumsy, if language allows, it would be great to know.
sorry for nuisance.

You can use dot-operators like .> in Julia for your first question:

julia> x = [1 3 78 98 11]
1×5 Array{Int64,2}:
 1  3  78  98  11

julia> y = x .> 60
1×5 BitArray{2}:
 false  false  true  true  false

julia> x[y]
2-element Array{Int64,1}:

and fill() for your second question:

julia> fill(NaN, 10, 10)

You can read the new docstring here; not merged yet because, for something really robust, there’s work to do in Interpolations.jl, and I may not get to it instantly. But it should be good enough to get you started.


thanks very much both!
I will check “warp” and let know, if it performs as expected.

Great, the transform works, however i didn’t find how to extract correctly the central part in the resulting image. So I did it manually.

As I need only a rotation about center, I wrote the following helper to cut it shorter:

# rotate image "I" around its centre by "angle" [degrees]
# returns or "full" or "central" part of the rotated image
function imrotate(I,angle,spec::String="central")

  tform = recenter(RotMatrix(angle/180*pi), center(I))
  Irot = parent(warp(I,tform))

  if (spec=="full")
  elseif (spec=="central")
    szX,szY = size(I)
    Dx = Int64(round(szX/2))
    Dy = Int64(round(szY/2))
    x0 = Int64(round(center(Irot)[1]))
    y0 = Int64(round(center(Irot)[2]))
    Ifin = Irot[x0-Dx+1:x0-Dx+szX,y0-Dy+1:y0-Dy+szY]


Unsure if I understand your intend, by try if the following code does what you intend. Basically I assume you would like to rotate around the center of the original image and not expand it’s size in any direction

using ImageTransformations, CoordinateTransformations, TestImages

img = testimage("camera")
tfm = recenter(RotMatrix(π/4), center(img))
imr = warp(img, tfm)
img_new  = imr[UnitRange.(indices(img))...]

many thanks, this is exactly a thing I was looking for!

Hey @Evizero,I was looking for something exactly like this…last line doesn’t seem to work due to
UndefVarError: indices not defined
How to correct that??

If you’re trying out old code (prior to the release of Julia 1.0), download a copy of Julia 0.7 and try it there: it will give you helpful hints about what the new names are.

In this case, use axes instead of indices.

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