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Question

Convert CIE Lch to CIE Lab

Forum|Forum|10 months ago
June 18, 2025
1 reply
255 views

With the help of Grok, I wrote a small script to convert CIE Lch to CIE Lab and store the result in the Swatches palette. Adobe has never wanted to support CIE Lch in any of their applications. Yet, I find it invaluable, especially for teaching color concepts.

The code is available here :
Convert CIE Lch to CIE Lab (with Debug code 2025 06 18).zip

I left the debug information in the file in case it helps anyone.
You don't have to remove it to execute the script.

Scripting

m1b

Community Expert

Thanks for sharing @Roger Breton!

Some minor notes: It's fine to leave debugging code in—sometimes it's very helpful!—but it's best to comment it out with // so that it doesn't actually try to run. Also most of your "debugging" code (writelns) were surely helpful during *initial development* but will never be needed again, so those could be discarded if you wanted.

Also, would you mind editing your post to include the actual script, since it isn't long in the listing? You can use the </> button in the forum editor, which formats the code like this:

... code here ...

That will make it so much easier for people to access your script, even if your one drive account goes stale, and also doesn't involve deciding whether it's safe to open a zip file from someone on the internet. 🙂

Anyway, thanks again—great contribution!

- Mark

Roger BretonAuthor

Legend

</>

// LchColorPicker.jsx

// Create a dialog for CIE Lch color input and conversion to Lab

try {

// Get the active document

var doc = app.activeDocument;

$.writeln("Active document accessed successfully.");

// Function to convert Lch to Lab

function lchToLab(l, c, h) {

var h_rad = (h * Math.PI) / 180;

var a = c * Math.cos(h_rad);

var b = c * Math.sin(h_rad);

return [l, a, b];

}

// Function to validate input values

function validateInputs(l, c, h) {

if (isNaN(l) || l < 0 || l > 100) {

alert("L value must be between 0 and 100.");

return false;

}

if (isNaN(c) || c < 0) {

alert("Chroma value must be non-negative.");

return false;

}

if (isNaN(h) || h < 0 || h > 360) {

alert("Hue value must be between 0 and 360 degrees.");

return false;

}

return true;

}

// Create dialog window

var dialog = new Window("dialog", "Convert CIE Lch to CIE Lab");

dialog.orientation = "column";

dialog.alignChildren = "left";

$.writeln("Dialog created.");

// Add input fields for L, c, h

var lGroup = dialog.add("group");

lGroup.add("statictext", undefined, "L (0-100): ");

var lInput = lGroup.add("edittext", undefined, "50");

lInput.characters = 3;

var cGroup = dialog.add("group");

cGroup.add("statictext", undefined, "Chroma (0-99): ");

var cInput = cGroup.add("edittext", undefined, "30");

cInput.characters = 2;

var hGroup = dialog.add("group");

hGroup.add("statictext", undefined, "Hue (0-360): ");

var hInput = hGroup.add("edittext", undefined, "45");

hInput.characters = 3;

// Add buttons

var buttonGroup = dialog.add("group");

var okButton = buttonGroup.add("button", undefined, "OK", {name: "ok"});

var cancelButton = buttonGroup.add("button", undefined, "Cancel", {name: "cancel"});

$.writeln("Dialog components added.");

// Variables to store input values and dialog result

var inputValues = null;

var dialogResult = 0;

// OK button functionality

okButton.onClick = function() {

try {

var l = parseFloat(lInput.text);

var c = parseFloat(cInput.text);

var h = parseFloat(hInput.text);

$.writeln("OK clicked. L: " + l + ", c: " + c + ", h: " + h);

if (!validateInputs(l, c, h)) {

return;

}

inputValues = { l: l, c: c, h: h };

$.writeln("Input values stored: L=" + l + ", c=" + c + ", h=" + h);

dialogResult = 1; // Explicitly set OK result

dialog.close(1); // Pass 1 to close

$.writeln("Dialog close called with result 1.");

} catch (e) {

$.writeln("Error in OK button: " + e);

alert("Error in OK button: " + e);

}

};

// Cancel button functionality

cancelButton.onClick = function() {

$.writeln("Cancel clicked.");

dialogResult = 2;

dialog.close(2);

$.writeln("Dialog close called with result 2.");

};

// Show the dialog

$.writeln("Showing dialog...");

var result = dialog.show();

$.writeln("Dialog.show returned: " + result + ", dialogResult: " + dialogResult);

if (dialogResult == 1 && inputValues != null) {

$.writeln("Processing color with L: " + inputValues.l + ", c: " + inputValues.c + ", h: " + inputValues.h);

var l = inputValues.l;

var c = inputValues.c;

var h = inputValues.h;

var labValues = lchToLab(l, c, h);

var labL = labValues[0];

var labA = labValues[1];

var labB = labValues[2];

// Create new Lab color

var newColor = doc.colors.add({

name: "Lch_L" + l.toFixed(0) + "_c" + c.toFixed(0) + "_h" + h.toFixed(0),

model: ColorModel.PROCESS,

space: ColorSpace.LAB,

colorValue: [labL, labA, labB]

});

$.writeln("Color created: " + newColor.name);

// Apply color to selected item if applicable

if (doc.selection.length > 0) {

var selectedItem = doc.selection[0];

if (selectedItem.fillColor != undefined) {

selectedItem.fillColor = newColor;

$.writeln("Color applied to selected item.");

} else {

$.writeln("Selected item does not support fill color.");

}

} else {

$.writeln("No item selected.");

}

// Show confirmation

alert("Color added to Swatches palette:\n" +

"L: " + labL.toFixed(2) + "\n" +

"a: " + labA.toFixed(2) + "\n" +

"b: " + labB.toFixed(2));

} else {

$.writeln("Dialog cancelled or no valid input (dialogResult: " + dialogResult + ").");

}

} catch (e) {

alert("Script error: " + e + "\nLine: " + e.line);

$.writeln("Error: " + e + ", Line: " + e.line);

}

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