How does one force an image to a defined color palette?

Question

I'm trying to limit the colors displayed in an RGB image but I'm not sure how to go about doing. I have a palette of 454 colors (so indexed color is not an option) and I would like to force my image to that color space. This may seem like an odd request, but there's actually a (theoretically) logical reason for it: in a nutshell, I have a swatch palette that corresponds to colors of a particular brand of thread and I want to fit the image's colors to the nearest thread color. While I might be able to do that by eye, I have 454 choices to choose from (laborious!) and I'd prefer to automate the process by letting Photoshop's adaptive color conversion algorithms do their magic.
Or am I overlooking something obvious?
I appreciate any suggestions or assistance!

Answer 1

Charles,
I went ahead and cobbled together a script from other's code to generate a directory full of 100x100 72dpi jpg swatches from a CSV list of names, R, G, and B values. I fed the 454-file directory to MacOSaix and I'm letting it do it's thing. Thanks for the suggestion!
I doubt it will be of any value to anyone, but here's the script, just in case:
#target Photoshop
function main() {
     if (isOSX()) {
          var csvFile = File.openDialog('Select a CSV File', function (f) { return (f instanceof Folder) || f.name.match(/\.csv$/i);} );
     } else {
          var csvFile = File.openDialog('Select a CSV File','comma-separated-values(*.csv):*.csv;');
     if (csvFile != null) {
          fileArray = readInCSV(csvFile);
          var columns = fileArray[0].length;
          //alert('CSV file has ' + columns + ' columns…');
          var rows = fileArray.length;
          //alert('CSV file has ' + rows + ' rows…');
          if (columns == 4 && rows > 0) {
               generateSwatches(csvFile);
          } else {
               var mess = 'Incorrect CSV File?';
               isOSX ? saySomething(mess) : alert(mess);
     } else {
          var mess = 'Ooops!!!';
          isOSX ? saySomething(mess) : alert(mess);
main();
function generateSwatches(csvFile,directory) {
     var docRef = app.documents.add();
     with (docRef) {    
//         for (var i = unusedSwatches.length-1; i >= 0; i--) {
//              unusedSwatches[i].remove();
           var directory=csvFile.path;
          for (var a = 0; a < fileArray.length; a++) {
               var filename = fileArray[a][0] +".jpg"; // First Column is name for file                     
               r = parseFloat(fileArray[a][1]); // Second Column is Red
               g = parseFloat(fileArray[a][2]); // Third Column is Green
               b = parseFloat(fileArray[a][3]); // Forth Column is Blue
               if (r >= 0 && r <= 255 && g >= 0 && g <= 255 && b >= 0 && b <= 255) {
                    SaveJPEG(filename, directory, r, g, b);
               } else {
                    var mess = 'Color values are out of range?';
                    isOSX ? saySomething(mess) : alert(mess);
function readInCSV(fileObj) {
     var fileArray = new Array();
     fileObj.open('r');
     fileObj.seek(0, 0);
     while(!fileObj.eof) {
          var thisLine = fileObj.readln();
          var csvArray = thisLine.split(',');
          fileArray.push(csvArray);
     fileObj.close();
     return fileArray;
function saySomething(stringObj) {
     var speakThis = 'say "' + stringObj + '" using "Fred"';
     app.doScript(speakThis, 1095978087); // AppleScript
function isOSX() {
  return $.os.match(/Macintosh/i);
function SaveJPEG(filename, directory, r, g, b){
      // create doc
   app.preferences.rulerUnits = Units.PIXELS
   var doc = app.documents.add(100, 100, 72, filename,);
    // define your fill color
   var color = new SolidColor();
   color.rgb.red = r;
   color.rgb.green = g;
   color.rgb.blue = b;
   var imagefile = new File(directory+"/"+filename);
   jpgSaveOptions = new JPEGSaveOptions();
   jpgSaveOptions.embedColorProfile = true;
   jpgSaveOptions.formatOptions = FormatOptions.STANDARDBASELINE;
   jpgSaveOptions.matte = MatteType.NONE;
   jpgSaveOptions.quality = 12; //JPEG quailty (1-12)
      // fill layer
   doc.selection.selectAll();
   doc.selection.fill(color);
    activeDocument.saveAs(imagefile, jpgSaveOptions, true ,Extension.LOWERCASE);
   // close document
   doc.close(SaveOptions.DONOTSAVECHANGES);
(Is this overkill and wildly unnecessary? Of course it is.)