Draw line between black pixel : coordinates of selected pixels ?

Question

Hi
I want to build a script which can check a Photoshop file and :
- find black pixel
- for each black pixel, look for another black pixel within maximum distance of 5 pixels
- then draw a line between the two black pixels.
I wrote this script below (my first script ...), but it's VERY slow (and my final image is VERY big), I think because I test the colour for each pixel of the image.
So another solution would be to first select black pixel with magic wand, then the script save all coordinates of selected pixels, then my script wil test only this pixels (less than 1% of the pixels are black in my image).
Is it possible with JavaScript ?
Thank you for your response !
Marc
function main(){
var startRulerUnits = app.preferences.rulerUnits;
app.preferences.rulerUnits = Units.PIXELS;
var myHeight = app.activeDocument.height;
var myWidth = app.activeDocument.width;
// Find black pixel
for(var i=5; i<myWidth; i++) {
  for(var j=5; j<myHeight; j++) {
   activeDocument.colorSamplers.removeAll()
   var sampler = activeDocument.colorSamplers.add([new UnitValue (i, 'px'), new UnitValue (j, 'px')]);
   if (sampler.color.rgb.hexValue === "000000") {
// For each black pixel, search another black pixel below left up to 5 pixels
    for (var m=i-5; m<i; m++) {
     for (var n=j+1; n<j+5; n++) {
      activeDocument.colorSamplers.removeAll()
      var test = activeDocument.colorSamplers.add([new UnitValue (m, 'px'), new UnitValue (n, 'px')]);
      if (test.color.rgb.hexValue === "000000") {
// Then draw a black line between the two black pixels
       var FillColour = new SolidColor;
       FillColour.rgb.hexValue = '000000';
       var ad=activeDocument;
       ad.selection.select([[m,n],[i,j],[m,n+1],[i,j+1]], SelectionType.REPLACE, 0, true);
       ad.selection.fill(FillColour);
       ad.selection.deselect()
// For each black pixel, search another black pixel below right up to 5 pixels
     for (var m=i+1; m<i+5; m++) {
      for (var n=j; n<j+5; n++) {
       activeDocument.colorSamplers.removeAll()
       var test = activeDocument.colorSamplers.add([new UnitValue (m, 'px'), new UnitValue (n, 'px')]);
       if (test.color.rgb.hexValue === "000000") {
// Then draw a black line between the two black pixels
        var FillColour = new SolidColor;
        FillColour.rgb.hexValue = '000000';
        var ad=activeDocument;
        ad.selection.select([[i,j],[m,n],[m,n+1],[i,j+1]], SelectionType.REPLACE, 0, true);
        ad.selection.fill(FillColour);
        ad.selection.deselect()
main();

Answer 1

The first alert should have shown the first pathPoint.anchors for all the subPaths in the path.
The xyArray is just something I added for the alerts. The array 'myPathInfo' should have all the info extracted from the path.
myPathInfo.length will tell you how many subPaths are in the Path.
myPathInfo[index].entireSubPath.length will tell you how many pathPoints are in that subPath
myPathInfo[index].entireSubPath[index].anchor will tell you the position of that pathPoint.
The indexes start with zero.
The bounding box of the entire subPath can be hard to work out just from the pathPoints. Unless all the point are corner points the path may extend beyond the anchors. One think you can do is create a new path from just one of the subPaths, convert by to a selection, and then get the bounds from the selection. You can make a new path from a subPath using the 'myPathInfo' array from above.
app.activeDocument.pathItems.add("myPath1", [myPathInfo[0]]);
That line will make a new path from the first subPath. Change the index to use a different subPath.
Some other info that may help.
app.activeDocument.histogram[0] will tell you how may black pixels are in the document. But its no help determining where they are. If that returns 0 there are no black pixels.
If you don't have any luck working with converting the original color range selection into a path and need to go back to searching with the colorSampler it may help to use a grid approach. For example make a square selection, the size depending on how scattered the black pixels are, say 25x25px. Then use color range to select black. With an active selection it will only select pixels in that selected area( if any). You could then check to see if there is a selection. If not make another same size square to the right edge of the last area. If there is a selection, the solid property will tell you if more than one black pixel was selected( unless they are right next to each other ). If solid == true the selection bounds will tell you where the pixel is. If false you have to then search that square. But if there are areas where there are no black pixels checking a square range of pixels at once should be quite a bit faster than checking every pixel. And checking the historgram first will let you know if you should bother searching to start with.