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I am currently trying to partition an image into several images with fixed size and no padding spanning the whole area of the original. Subsequently, I want to do an arbitrary operation on each image part and reassemble the image by overlaying the results of this operation (repeated entries could be replaced by a mean). This would mean that the image parts have variable offset and overlay with each other depending on the size of the original.

As far as I understand it the offset of ImagePartition is fixed and ImageAssemble can only work with parts that do not have any overlays.

It should be something like the following:

im = Import["ExampleData/spikey.tiff"]
(*this operation should give as many 100x100 images as are needed to cover all pixels of im possibly having considerable overlap*)
parts = ImagePartitionSpecial[im, {100, 100}]     
parts = DoArbitraryImageOperation@parts
(*this operation should assemble an image of the size im where repeated pixels should be replaced by a mean of them*)
result = ImageAssembleSpecial[parts] 

Has something like this been done before? Essentially my function only works on images of a fixed size so that I need to disassemble and reassemble the image I want to call it on. Note that setting a fixed offset of 1 would not be great as this will generate way too many parts.

Best, Max

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im = Import["ExampleData/spikey.tiff"];

The following function makes intervals with size sz that covers Range[dim]

ints[dim_, sz_] := With[{mids = Range[(1 + sz)/2, ((dim - sz + 1) + dim)/2,
 (dim - sz)/Max[Quotient[dim, sz, 1], 1]]}, Floor[Outer[Plus, mids, {1 - sz, sz - 1}/2]]]

Combining such intervals in both image dimensions we get the subimage coordinates

subImageCoords[im_, w_, h_] := Outer[List, Sequence @@ Reverse[
                                MapThread[ints, {ImageDimensions[im], {w, h}}]], 1]

assem partitions with overlay using subimages with width w and height h. Then it applies some transformation trans to all subimages, and finally combines the subimages using ImageAdd (after dividing the overlay pixels by 2).

trans = Identity;

assem[im_, w_, h_] := Module[{data, makeTermRow, makeTermCol},

  makeTermRow = Function[{image, overlay, pad},
                         data = ImageData[image];
                         data[[;; overlay[[1]]]] /= 2;
                         data[[-overlay[[2]] ;;]] /= 2;
                         ImagePad[Image[data], {{0, 0}, pad}]];

  makeTermCol = Function[{image, overlay, pad},
                         data = ImageData[image];
                         data[[All, ;; overlay[[1]]]] /= 2;
                         data[[All, -overlay[[2]] ;;]] /= 2;
                         ImagePad[Image[data], {pad, {0, 0}}]];

  With[{pos = subImageCoords[im, w, h], imDim = ImageDimensions[im]},

    With[{newImages = Map[trans[ImageTake[im, Sequence @@ #]] &, pos, {2}],
          newDim = Dimensions[pos]},

      With[{newRows = ImageAdd /@ MapThread[makeTermCol, {newImages,
         ConstantArray[ArrayReshape[{0, w - Differences[pos[[1, All, 2]]], 0}, newDim[[{2, 3}]]], newDim[[1]]],
         ConstantArray[Transpose[Transpose[pos[[1, All, 2]]] {1, -1} - {1, -imDim[[1]]}], newDim[[1]]]}, 2]},

                      ImageAdd[MapThread[makeTermRow, {newRows,
         ArrayReshape[{0, h - Differences[pos[[All, 1, 1]]], 0}, newDim[[{1, 3}]]],
         Transpose[(Transpose[pos[[All, 1, 1]]] {1, -1} - {1, -imDim[[2]]})[[{-1, 1}]]]}]]]]]]

Now modify trans and call assem[im, 100, 100]

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