6 Replies Latest reply on Nov 7, 2018 7:11 AM by diarmaidu763947

    Find midpoint of irregular shaped area


      Hi everyone

      can anyone help me with this problem?

      I have several of these irregular shaped areas. Now I would need to calculate the midpoint of the areas in question.

      Does anyone have a tutorial or similar how I could do that?

      the picture below is an example:


      Thanks a lot


        • 1. Re: Find midpoint of irregular shaped area
          Test Screen Name Most Valuable Participant

          That sounds like something for a specialist tool, not a photo editor. You also need to consider that "midpoint" is ambiguous:

          * centre of gravity (if this were a solid of uniform density)

          * centre of the smallest containing rectangle aligned with grid

          * centre of the smallest containing circle

          * point at the centre of the longest line between two points on the outside boundary

          * average of a large number of x,y sample points randomly or uniformly arranged inside the shape

          * or many more...

          1 person found this helpful
          • 2. Re: Find midpoint of irregular shaped area
            Trevor.Dennis Adobe Community Professional

            Hi Michael


            I'm wondering what criteria you would use to decide on the midpoint?  I keep coming back to it being half way between the extremities when considering the object as a rectangle.  If you were to select the area and copy to a new layer.  Using Free Transform would place the centre handle at that half way point.  Making a copy and reducing it in size, will cause it to reduce around that same centre handle.


            I don't think this can be what you are looking for, so it would help — me at least — to know what criteria you want to use.

            • 3. Re: Find midpoint of irregular shaped area
              davescm Adobe Community Professional

              If you want to find the centre of gravity - which would normally be considered the midpoint of an irregular shape, you can do it in Photoshop although it is a little awkward.


              1. Draw around your shape with the pen tool to create a shape and fill it with a solid color. Then turn off your image layer.

              2. Use Select color range to make a selection of your color and in the histogram, expanded view, ensure Cache level is 1 (if not click the triangle at the top right of the histogram). Then read the number of pixels (in my case 4836668)

              3. Calculate half that number of pixels - so for me 2418334

              4. Add a white rectangle shape just above the irregular shape layer and position the edge approximately halfway down.

              5. Press Ctrl+D to Deselect and select color range again

              6.Read the number of pixels in the histogram - remember you must be at cache level 1 so click the warning triangle if not.

              7. Move the white rectangle up/down and repeat steps 5 & 6 until you have as close as possible half the pixels as calculated in 3.

              8. Drag a guide from the ruler an position it on the edge

              9. Move the rectangle so it's vertical edge is across the shape and repeat steps 4-8


              10. Your guides are in the centre of gravity so you can now turn off the shape layers and turn the image back on


              Like I said - it is a bit awkward - but it does work.


              I hope that helps



              2 people found this helpful
              • 4. Re: Find midpoint of irregular shaped area
                c.pfaffenbichler Level 9

                Good one.

                It should be possible to script something on the basis of that approach bit it might not be exactly speedy.

                • 5. Re: Find midpoint of irregular shaped area
                  c.pfaffenbichler Level 9

                  The below Script intends to mark that point for a black area on white with two guides (no guarantees, though).


                  // mark »center« on black are on white.

                  // based on paul riggott’s code for raw image assessment;

                  // 2018, use it at your own risk;

                  #target photoshop

                  File.prototype.readByte = function() {

                  return this.read(1).charCodeAt(0);


                  if (app.documents.length > 0) {

                  var originalRulerUnits = app.preferences.rulerUnits;

                  app.preferences.rulerUnits = Units.PIXELS;

                  var myDocument = app.activeDocument;

                  var theDup = myDocument.duplicate ("dup", true);

                  theDup.changeMode (ChangeMode.GRAYSCALE);


                  theDup.selection.load(theDup.channels[0], SelectionType.REPLACE, true);


                  var theBounds = theDup.selection.bounds;


                  theDup.changeMode (ChangeMode.LAB);

                  var theResult = somethingSomething();

                  theDup.close (SaveOptions.DONOTSAVECHANGES);

                  activeDocument = myDocument;

                  myDocument.guides.add(Direction.VERTICAL, theResult[4] + theBounds[0]);

                  myDocument.guides.add(Direction.HORIZONTAL, theResult[5] + theBounds[1]);

                  app.preferences.rulerUnits = originalRulerUnits;



                  function convertByteToSignedByte(num){

                  var dec = (num | (num % 256))-128

                  return dec;


                  function convertByteToLum( num){

                  var dec = Math.round((num/256)*100);

                  return dec;


                  // get arrays of sums of non-white pixels per line and column;

                  function somethingSomething (){

                  if(!documents.length) return;

                  if(activeDocument.mode != DocumentMode.LAB) {

                      alert("Please convert this document to Lab mode\r Then re-run this script");



                  var Name = decodeURI(app.activeDocument.name).replace(/\.[^\.]+$/, '');


                  var Path = activeDocument.path;

                  }catch(e){var Path = '~/Desktop';}

                  var rawFile = new File(Path +"/"+Name +".raw");


                  var len = 0;

                  var W = activeDocument.width.as('px');



                  rawFile.encoding = 'BINARY';


                  // result arrays;

                  var theLines = new Array;

                  var theColumns = new Array;

                  for (var y = 0; y < W; y++) {theColumns.push(0)};

                  var theLine = 0;

                  ////// work through //////


                  var theL = 100-(convertByteToLum(rawFile.readByte()));

                  var theA = convertByteToSignedByte(rawFile.readByte());

                  var theB = convertByteToSignedByte(rawFile.readByte());


                  theColumns[CountW] = theColumns[CountW]+theL/100;

                  // new line;

                  if(len % W == 0){


                  theLine = 0;





                  theLine = theLine + (theL/100);



                  // remove raw file;



                  var theSum = 0;

                  var theSumColumn = 0;

                  for (var x = 0; x < theLines.length; x++) {theSum = theSum + theLines[x]};

                  for (var x = 0; x < theColumns.length; x++) {theSumColumn = theSumColumn + theColumns[x]};

                  var resultHor = midValue (theLines, theSum);

                  var resultVer = midValue (theColumns, theSumColumn);


                  activeDocument.guides.add(Direction.VERTICAL, resultVer);

                  activeDocument.guides.add(Direction.HORIZONTAL, resultHor);

                  // return results;

                  return [theLines, theSum, theColumns, theSumColumn, resultVer, resultHor]


                  function saveAsRaw(file) {

                  var desc1 = new ActionDescriptor();

                  var desc2 = new ActionDescriptor();

                  desc2.putString( charIDToTypeID('FlCr'), "8BIM" );

                  desc2.putBoolean( charIDToTypeID('ChnI'), true );

                  desc1.putObject( charIDToTypeID('As  '), charIDToTypeID('Rw  '), desc2 );

                  desc1.putPath( charIDToTypeID('In  '), new File( file ) );

                  desc1.putBoolean( charIDToTypeID('Cpy '), true );

                  executeAction( charIDToTypeID('save'), desc1, DialogModes.NO );



                  function midValue (theArray, theSum) {

                  var theX = 0;

                  var theHalf = theSum/2;

                  for (var n = 0; n < theArray.length; n++) {

                  theX = theX + theArray[n];

                  if (theX == theHalf) {return n+1};

                  if (theX > theHalf) {

                  var thePercentage = theX/theSum;

                  var theDiff = 0.5 + ( ( (theSum - theX) / theSum) - ( (theX - theArray[n]) / theSum) ) * 0.5 / (theArray[n] / theSum);

                  return n+theDiff};



                  2 people found this helpful
                  • 6. Re: Find midpoint of irregular shaped area
                    diarmaidu763947 Level 1


                    1. Select Shape

                    2. Copy Shape

                    3. Paste Shape in place

                    4. Select copy

                    5. OBJECT-PATH-AVERAGE-BOTH_OK


                    How to Find the Center of a Star in Adobe Illustrator - YouTube

                    1 person found this helpful