matchColours.jsx

// enable double clicking
#target photoshop
app.bringToFront();

var doc = activeDocument,
    docName = activeDocument.name;

// Save the current preferences
var startRulerUnits = app.preferences.rulerUnits,
    startTypeUnits = app.preferences.typeUnits,
    startDisplayDialogs = app.displayDialogs;

// Set Adobe Photoshop CC 2015 to use pixels and display no dialogs
app.preferences.rulerUnits = Units.PIXELS;
app.preferences.typeUnits = TypeUnits.PIXELS;
app.displayDialogs = DialogModes.NO;

var outputFile = '~/Desktop/Lab_' + docName.slice(0, -4) + '.csv', //output
    sampler = doc.colorSamplers.add([0, 0]),
    lumRange = (100 / 6),
    lum1 = [],
    lum2 = [],
    lum3 = [],
    lum4 = [],
    lum5 = [],
    lum6 = [],
    blnk = [,,,,];

initFile(outputFile);
doc.convertProfile("Lab Color", Intent.RELATIVECOLORIMETRIC, true, true );
if(doc.width > 30){
    doc.resizeImage(null,UnitValue(30,"px"), null, ResampleMethod.NEARESTNEIGHBOR);
}

for (var y = 0; y < doc.height; ++y) {
    for (var x = 0; x < doc.width; ++x) {        

        sampler.move([x, y]);
        var color = sampler.color,
            l = (color.lab.l).toFixed(2),
            a = (color.lab.a).toFixed(0),
            b = (color.lab.b).toFixed(0);
        
        if(l <= lumRange){
            lum1 = [l,a,b];
            writeToFile(outputFile, lum1);
            $.writeln(lum1);         //debug
            $.writeln('**********'); //debug
        } else if (l > lumRange   && l <= lumRange*2){
            lum2 = [l,a,b];
            writeToFile(outputFile, blnk+lum2);            
            $.writeln(lum2);         //debug            
            $.writeln('**********'); //debug           
        } else if (l > lumRange*2 && l <= lumRange*3){
            lum3 = [l,a,b];
            writeToFile(outputFile, blnk+blnk+lum3);            
            $.writeln(lum3);         //debug
            $.writeln('**********'); //debug
        } else if (l > lumRange*3 && l <= lumRange*4){
            lum4 = [l,a,b];
            writeToFile(outputFile, blnk+blnk+blnk+lum4);            
            $.writeln(lum4);         //debug
            $.writeln('**********'); //debug           
        } else if (l > lumRange*4 && l <= lumRange*5){
            lum5 = [l,a,b];
            writeToFile(outputFile, blnk+blnk+blnk+blnk+lum5);            
            $.writeln(lum5);         //debug
            $.writeln('**********'); //debug           
        } else {
            lum6 = [l,a,b];
            writeToFile(outputFile, blnk+blnk+blnk+blnk+blnk+lum6);            
            $.writeln(lum6);         //debug
            $.writeln('**********'); //debug
        }
        
        //writeToFile(outputFile, lum1.concat(lum2, lum3, lum4, lum5, lum6));
        
        //lum1 = [,,,]; lum2 = [,,,]; lum3 = [,,,];
        //lum4 = [,,,]; lum5 = [,,,]; lum6 = [,,,];
    }
}

function writeToFile(fileName, text){
    var csvFile = new File(fileName);
    csvFile.open("a");
    csvFile.writeln(text);
    csvFile.close();
}

function initFile(fileName){
    var csvFile = new File(fileName);
    csvFile.open("w");   
    csvFile.writeln(docName + "\nL1,a,b,L2,a,b,L3,a,b,L4,a,b,L5,a,b,L6,a,b");
    csvFile.close();
}

//clean up
doc.activeHistoryState = doc.historyStates[0];
app.purge(PurgeTarget.HISTORYCACHES);  

alert("Complete");

Desired Output

Test file pixel values expressed from left to right and top to bottom