Function Repository Resource:

ImageTakeAt

Source Notebook

Get a part of an image at a specified position with specified dimensions

Contributed by: AMP

ResourceFunction["ImageTakeAt"][image, center, dimensions]

takes a part of the image around the specified center position up to the requested dimensions.

ResourceFunction["ImageTakeAt"][image, center, dimensions, background]

takes a part of the image with the given dimensions, padding with background as needed.

Details

ResourceFunction["ImageTakeAt"][image, center, dimensions, background] uses ImagePad[subimage, background] to set the background color and pad the subimage.

Only for two odd-valued subimage dimensions, the image part will be exactly centered around specified center position. For an even-valued subimage dimensions, to avoid image content interpolation, the resulting subimage will be taken half a pixel upwards and/or to the left relative to the specified center.

ResourceFunction["ImageTakeAt"] currently only works for 2D images.

Examples

Basic Examples (5)

Get a test image of the moon:

In[1]:=

(* Evaluate this cell to get the example input *) CloudGet["https://www.wolframcloud.com/obj/2e54979f-7b33-4bf0-bfa9-17317a0edcea"]

Get a subimage:

In[2]:=

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Here, the size of the subimage is smaller than requested since its center was at the image’s border:

In[3]:=

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Take an image part and pad it with the specified background color to obtain the requested dimensions:

In[4]:=

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Verify that the results have the expected sizes:

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Scope (5)

Define a pattern image:

In[6]:=

$pattern = \!\(\* GraphicsBox[ TagBox[RasterBox[ RawArray["Real32",{{{1., 1., 1.}, {0.5646560788154602, 0.08474795520305634, 0.5619234442710876}, {1., 1., 1.}, { 0.03348027169704437, 0.4300873279571533, 0.7157250046730042}, {1., 1., 1.}}, {{0.8329219222068787, 0.7105229496955872, 0.7314381003379822}, {1., 1., 1.}, { 0.5976433753967285, 0.667712390422821, 0.7099030613899231}, { 1., 1., 1.}, {0.7506136298179626, 0.28365862369537354`, 0.33173638582229614`}}, {{1., 1., 1.}, {0.08899957686662674, 0.6156218647956848, 0.5254729986190796}, {1., 1., 1.}, { 0.31468233466148376`, 0.021926982328295708`, 0.45569929480552673`}, {1., 1., 1.}}, {{0.7631984949111938, 0.6360676288604736, 0.18542690575122833`}, {1., 1., 1.}, { 0.17495205998420715`, 0.8324634432792664, 0.9552257657051086}, {1., 1., 1.}, {0.5285191535949707, 0.6361931562423706, 0.3614344000816345}}, {{1., 1., 1.}, { 0.7412189245223999, 0.00879684928804636, 0.4472665786743164}, {1., 1., 1.}, {0.7703076004981995, 0.04790664464235306, 0.8185895681381226}, {1., 1., 1.}}}], {{0, 5.}, {5., 0}}, {0., 1.}, ColorFunction->RGBColor], BoxForm`ImageTag["Real32", ColorSpace -> "RGB", Interleaving -> True], Selectable->False], DefaultBaseStyle->"ImageGraphics", ImageSize->{28.25, Automatic}, ImageSizeRaw->{5., 5.}, PlotRange->{{0, 5.}, {0, 5.}}]\);$

Show the pattern image with Axes for pixel coordinates:

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$ArrayPlot[ImageData[ColorNegate@pattern], ImageSize -> 100, Frame -> True, FrameTicks -> Evaluate[{Transpose[{#, Reverse[#]}], #} &[ Range[ImageDimensions[pattern][[1]]]]], Epilog -> Text["\[Times]", center - 0.5]]$

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Take a 3×3 subimage centered at {3,3}:

In[8]:=

$odd = ResourceFunction["ImageTakeAt"][pattern, center = {3, 3}, {3, 3}]; ArrayPlot[ImageData[ColorNegate@odd], ImageSize -> 100, Frame -> True, FrameTicks -> Evaluate[{Transpose[{#, Reverse[#] + 1}], Transpose[{#, # + 1}]} &[ Range[ImageDimensions[odd][[1]]]]], Epilog -> Text["\[Times]", center - 1 - 0.5]]$

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Take a 2×2 subimage at {3,3}. It will be extracted half a pixel upwards and to the left of the specified center at {2.5, 3.5}:

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$even = ResourceFunction["ImageTakeAt"][pattern, {3, 3}, {2, 2}]; ArrayPlot[ImageData[ColorNegate@even], ImageSize -> 100, Frame -> True, FrameTicks -> Evaluate[{{Transpose[{#, Reverse[#] + 2}], None}, {Transpose[{#, # + 1}], None}} &[ Range[ImageDimensions[even][[1]]]]], Epilog -> {Text["\[Times]", center - {1, 2} - 0.5], Arrowheads[0.075], Arrow[{center - {1.5, 2.5}, center - {2, 2}}]}]$

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Take a 4×3 subimage at {3,3}. To avoid image interpolation, it will be extracted half a pixel to the left of the specified center at {2.5, 3}:

In[12]:=

$evenOdd = ResourceFunction["ImageTakeAt"][pattern, {3, 3}, {4, 3}]; ArrayPlot[ImageData[ColorNegate@evenOdd], ImageSize -> 100, Frame -> True, FrameTicks -> Evaluate[{{Transpose[{#, Reverse[#] + 0}], None}, {Transpose[{#, # + 0}], None}} &[ Range[ImageDimensions[evenOdd][[1]]]]], Epilog -> {Text["\[Times]", center - {0, 1} - 0.5], Arrowheads[0.075], Arrow[{center - {0.5, 1.5}, center - {1, 1.5}}]}]$