I have two screenshots:

For a long screenshot picture I usually use PhotoShop to combine both images:

How do I use Mathematica to make an automated program to do this?

Is there a smarter method?The ImageCorrespondingPoints should be helpful,but I I don't know how to realize it.


The @Arnoud Buzing's answer almost solve this problem,but there are TWO difficulties still to overcome

1. First difficulty:

As the answer we can build a function to do this:

MergeImage[image1_, image2_] := 
 Module[{i1 = ImageData[image1], i2 = ImageData[image2]},
  {s1, s2} = LongestCommonSubsequencePositions[i1, i2];
  Join[Take[i1, Last@s1], Take[i2, {Last@s2 + 1, -1}]] // Image]

But when the

image1 is image2 is

Due to the common subsequence is not the Longest,the long-screenshots will be wrongly merge.

2. Second difficulty:

The MergeImage we built cannot distinguish this ordring of these screenshots automatically.Such as we can run it MergeImage[image1, image2],But not MergeImage[image2, image1].There is a image3:

If our last MergeImage can run it like this to get the right long-screenshots,the problem have been solved.

MergeImage[RandomSample[{image1, image2, image3}]]
  • 1
    $\begingroup$ Life would be easier if you first crop out the top of image2, image3 etc before attempting anything automatic. $\endgroup$ – user484 Mar 6 '16 at 15:19
  • $\begingroup$ Possibly related: mathematica.stackexchange.com/q/32612/484 $\endgroup$ – user484 Mar 6 '16 at 15:22
  • $\begingroup$ @Rahul Because the image2image3 can be different picture completely.I just use SE's screenshots to express this kind of question in here.So If you wanna crop it manually,It is a very dull works.And your case of that link have no part which is juxtaposition each other. $\endgroup$ – yode Mar 6 '16 at 15:44
  • $\begingroup$ You don't need to crop it exactly, you just need to get rid of the top bar assuming you know roughly how big it is. $\endgroup$ – user484 Mar 6 '16 at 16:56

Very roughly (using image1 and image2):

i1 = ImageData[image1];
i2 = ImageData[image2];
css = LongestCommonSubsequence[i1, i2];
s1 = SequencePosition[i1, css];
s2 = SequencePosition[i2, css];
Join[Take[i1, s1[[1,2]] ], Take[i2, {s2[[1,2]] + 1, -1}]] // Image

That seems to work for me and gives the images concatenated together.

  • $\begingroup$ i1 = ImageData[image1]; i2 = ImageData[image2]; {s3, s4} = LongestCommonSubsequencePositions[i1, i2]; Join[Take[i1, Last@s3], Take[i2, {Last@s4 + 1, -1}]] // Image $\endgroup$ – yode Mar 6 '16 at 8:47
  • $\begingroup$ I have make this problem more clear just now.If you are available,you can take a try please. $\endgroup$ – yode Mar 6 '16 at 9:40

This solves your "entangled images" case.

ClearAll[getMinRowFromImage, getBestMatch, findAllMatches, joinImages,
         findImagesSequence, getIntensity];

getIntensity[i_Image, pos_List] :=
 (* Calculates the intensity of a pixel for any image color space.*)
 First@ColorConvert[Flatten@{PixelValue[i, pos]}, ImageColorSpace[i] -> "Grayscale"]

getMinRowFromImage[i_Image] :=
 (* returns the min intensity value for an image and the row where it occurs*)
 {getIntensity[i, #[[1]]], #[[1, 2]]} &@PixelValuePositions[i, "Min"]

getBestMatch[i_List, {m_Integer, n_Integer}, lines_Integer] :=
 (* Finds the best match between i[[n]] and the last lines of i[[m]].
 Note that "Padding -> None" is what allows this to run within 
 reasonable time, calculating the correlation only by rows and 
 thus returning single column image*)
 getMinRowFromImage@ImageCorrelate[i[[n]], ImageTake[i[[m]], -lines],
                                  CorrelationDistance, Padding -> None]

findAllMatches[i_List, lines_Integer, sens_Real] :=
 (*forms all permutations {m,n} from the list of images
 calculates the best match between all pairs and 
 select those below the sensitivity parameter
 Could be done more efficiently, since we expect only one 
 valid continuation foreach image, so we don't really need to 
 calculate them all*)
 With[{permutations = Position[IdentityMatrix[Length@i], 0]},
  Select[{#, getBestMatch[i, #, lines]} & /@ permutations, #[[2, 1]] < sens &]


findImagesSequence[g_Graph] :=
 (* g is  a directed PathGraph whose wheights are the best match lines 
 for each pair. So, the Max of the distance matrix is at the 
 {head, tail} pair. We  find the (only) path that goes from head
 to tail, hence finding the right image sequence. There is a function 
 in Mma help that does the same for undirected Graphs, but I think 
 this one is better for our purpose *)
 FindShortestPath[g, Sequence @@ VertexList[g][[First@Position[#, Max@#] &
                                          [GraphDistanceMatrix@g /. ∞ -> 0]]]]

joinImages[i_List, linesToMatch_Integer, sens_Real] :=
 (* Ensambles a full image from parts consisting in same column width 
 images matching from some row onwards for a minumum of "linesToMatch".
 The sensitivity parameter seeme not really needed but perhaps useful 
 for very similar images
 Module[{matches, g, seqimg, fromline},
  (* First find the pairs matching *)
  matches = findAllMatches[i, linesToMatch, sens];

  (*Now we build up the whole sequence, from head to tail.
  Graph features are great for that*)
  g = Graph[Rule @@@ #[[All, 1]], EdgeWeight -> Flatten@#[[All, 2, 2]]] &@matches;
  seqimg = findImagesSequence[g];
  fromline = PropertyValue[{g, DirectedEdge @@ #}, EdgeWeight] & /@ 
                                                        Partition[seqimg, 2, 1];

  (*Finally assemble the whole thing*)
    MapThread[{ImageTrim[#1, {{0, #2}, {ImageDimensions[#1][[2]], 0}}]} &,
              {i[[Rest@seqimg]], fromline}]]


l = {"http://i.stack.imgur.com/IXFEq.png",
(*Resize and GrayScale for speed*)
i = ImageResize[#, 500] & /@ (ColorConvert[#, "Grayscale"] & /@ Import /@ l);

sensitivity = .1;
lnsTomatch = 150;
joinImages[i, lnsTomatch, sensitivity]

Coloring not included in this code, used here to show how the image was composed from the three snapshots. The last step (the joining of images, excluding the import part) is instantaneous in my machine.

Mathematica graphics

  • $\begingroup$ "<del>Perhaps</del> I'll add some explanations" $\endgroup$ – Aisamu Mar 14 '16 at 22:21
  • $\begingroup$ It seem that you can reach the top of another mountain just cost my a nap time. $\endgroup$ – yode Mar 14 '16 at 23:19
  • $\begingroup$ The bounty expiring soon.I must choose a answer.But some bugs are exist still in this code.It'll give some error information when I run it like this.Look forward to your explanations and consummating it. $\endgroup$ – yode Mar 15 '16 at 14:13
  • $\begingroup$ Of course I have run that sentence of ImageResize.But the error imformations is still.And after this post,I'll take a good study of Graph Theory to follow your steps. $\endgroup$ – yode Mar 15 '16 at 15:41
  • 1
    $\begingroup$ @Aisamu Done :) $\endgroup$ – Dr. belisarius Mar 17 '16 at 16:31

This answer is late but stronger,I have packed it in a custom function and name after CombineImage.And since for merge some cell phone screenshots,the height should be same.Considering some APP has bottom menu bar,this answer actually can adapt that more complicated case than my original question

CombineImage[imgs_List] := 
 Module[{bottom, top, crop, data, threshold, height, bins, sortBins, 
   seq, oderImgs, order}, {bottom, top} = 
   Min /@ Transpose[
     BlockMap[Last[BorderDimensions[ImageSubtract @@ #]] &, imgs, 2]];
  crop = ImageTake[#, {top + 1, 
       Last[ImageDimensions[First[imgs]]] - bottom}] & /@ imgs;
  data = ImageData /@ crop;
  threshold = 
   Min[ImageMeasurements[ColorConvert[#, "Grayscale"] & /@ crop, 
  height = Last[ImageDimensions[First[crop]]];
  bins = Binarize[#, threshold] & /@ crop;
  sortBins = 
     Sign[N[Mean[#]/height] & /@ 
          LongestCommonSubsequencePositions @@ 
           ImageData /@ {##} - .5] === {1, -1} &, bins]];
  order = FindPermutation[bins, sortBins]; {oderImgs, data} = 
   Permute[#, order] & /@ {imgs, data};
  seq = Developer`PartitionMap[
    LongestCommonSubsequencePositions @@ # &, ImageData /@ sortBins, 
    2, 1];
    Take[ImageData[First[oderImgs]], seq[[1, 1, 1]] + top - 1], 
    Sequence @@ 
      Take, {data[[2 ;; -2]], 
       Partition[First /@ Catenate[seq][[2 ;; -2]], 2]}], 
     seq[[-1, -1, 1]] - bottom - height - 1]]]]


I have provided four images to test in following

imgs = Import /@ {"https://i.stack.imgur.com/gmfPU.png", 

Note I use a RandomSample to show I don't care the order of image list.

Code interpretation

Get the crop images which delete the margin on top and the bottom.Note the notification bar are not very accordance

{bottom, top} = 
 Min /@ Transpose[
   BlockMap[Last[BorderDimensions[ImageSubtract @@ #]] &, imgs, 2]];
crop = ImageTake[#, {top + 1, 
     Last[ImageDimensions[First[imgs]]] - bottom}] & /@ imgs

enter image description here Calculate a threshold for binarize the image for speed.And for showing all valid information as much as possible,I will use a mean value.We cannot use Grayscale here like this anser by Dr. belisarius,which will make the imgs have little difference even the part is same tatally.

data = ImageData /@ crop;
threshold = 
  Min[ImageMeasurements[ColorConvert[#, "Grayscale"] & /@ crop, 


If the following page will continue the above page,the follow centre must be larger than $50\%height$ of the image,this is a explanatory drawing when the next page cover $90%$ of the above.The center of the next is $5.5(>50\% height)$ still.

Since this,we can sort the imgs,I will use RelationGraph to do this

height = Last[ImageDimensions[First[crop]]];
bins = Binarize[#, threshold] & /@ crop;
toImgs = Thread[bins -> imgs];
toCrop = Thread[bins -> crop];
sortImgs = 
  RelationGraph[Sign[N[Mean[#]/height] & /@ 
        LongestCommonSubsequencePositions @@ 
         ImageData /@ {##} - .5] == {1, -1} &, bins]]

enter image description here

Use LongestCommonSubsequencePositions to find the overlapping part.Note we process all of imgs which have been croped.So when we recover it,we should use toImgs and toCrop

seq = Developer`PartitionMap[LongestCommonSubsequencePositions @@ # &,
    ImageData /@ sortImgs, 2, 1];
  Take[ImageData[First[sortImgs] /. toImgs], 
   seq[[1, 1, 1]] + top - 1], 
  Sequence @@ 
    Take, {Map[ImageData, sortImgs /. toCrop][[2 ;; -2]], 
     Partition[First /@ Catenate[seq][[2 ;; -2]], 2]}], 
  Take[ImageData[Last[sortImgs] /. toImgs], 
   seq[[-1, -1, 1]] - bottom - height - 1]]]

Then we get the long combine image.And I also give clor image for comparison enter image description here


Since this is an iphone screenshot, we know the exact pixel dimensions of the toolbar and so no fancy sequence matching need be done:

MergeImage[image1_, image2_] := Module[{i1, i2, i3},
  i1 = ImageData[image1][[;; 228]];
  i2 = ImageData[image1][[228 ;;]];
  i3 = ImageData[image2][[228 ;;]];
  Join[i1, i2, i3] // Image]

enter image description here

  • $\begingroup$ Thanks a lot for your answer,but maybe you misunderstand this topic.1.The screenshot from XiaoMi cell-phone(base in Andriod).2.Maybe ImageTake+ImageAssemble Can do what you have done.3.We have image1image2 and image3.And we want get a long screenshot by they,but they have some repeated part each other(you can look these picture carefully). $\endgroup$ – yode Mar 14 '16 at 7:53

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