Script to convert CIE Lab to CIE Lch?

[Roger Breton]

Looking for a way to work around InDesign limited color management capability.

Suppose I have some object selected on the page, the script would have to be able to extract the CIE Lab values out of the selected object, convert to Chroma and Hue angle, and paste the values in a new text frame. Doable? Easily?

[James Gifford—NitroPress]

I have no solution here but if there is one, there are a couple of color folks who will provide it.

I'm just curious how extracting/calculating this fairly esoteric color value... and then just pasting in text values, is of use. For some manual entry at a later point? Seems as if any color value calculator could do that...

[Roger Breton · Accepted solution]

Well, here's a simple script that displays an alert with the CIE Chroma and CIE Hue angle information.
InDesign HSB is useless because it is based on RGB. 
I am not by any means a JavaScript specialist.

The code is quite simple:

// Roger Breton / March 18 2024

// Get the active document

var doc = app.activeDocument;

// Check if there's a selection

if (doc.selection.length > 0) {

    // Get the first selected item

    var selectedItem = doc.selection[0];

    // Check if the selected item has a fill color

    if (selectedItem.fillColor !== undefined) {

        // Retrieve the fill color

        var fillColor = selectedItem.fillColor;

        var fillModel = selectedItem.fillColor.model.toString(); // SPOT

        var fillColorSpace = selectedItem.fillColor.space.toString(); // LAB

        var l_value = selectedItem.fillColor.colorValue[0];

        var a_value = selectedItem.fillColor.colorValue[1];

        var b_value = selectedItem.fillColor.colorValue[2];

        var l_float = parseFloat(l_value);

        var a_float = parseFloat(a_value);

        var b_float = parseFloat(b_value);

        // Calculate CIE Chroma (C)

        var chroma = Math.sqrt(Math.pow(a_value, 2) + Math.pow(b_value, 2));

        // Calculate Hue Angle (H) in radians

        var hue_radians = Math.atan2(b_value, a_value);

        // Convert Hue Angle to degrees

        var hue_degrees = (hue_radians * 180) / Math.PI;

        if (hue_degrees < 0) {

            hue_degrees += 360; // Make it positive

        }

        // Print the fill color details

        alert("Fill Color:\n\n" +

              "Color Model: " + fillModel + "\n" +

              "Color Space: " + fillColorSpace + "\n" +

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

              "A : " + a_value.toFixed(2) + "\n" +

              "B : " + b_value.toFixed(2) + "\n" +

              "Chroma : " + chroma.toFixed(2) + "\n" +

              "Hue Angle : " + hue_degrees.toFixed(2) + " degrees");

    } else {

        alert("The selected item does not have a fill color.");

    }

} else {

    alert("No item is currently selected.");

}

[Roger Breton]

It's difficult to directly interpret the a and b values of a Lab color.
The Hue angle is much more intuitive. 
Suppose I have two blue colors. If I know one has a hue angle of 257 and the other has a hue angle of 290 degrees then I can visualize abstractly the difference in appearance of those two colors. One (290) is more "purple" than the other, you see? 

[rob day]

Hi @Roger Breton A conversion to HSB would be the only option. InDesign’s HSB is not device independent, it’s color managed via the assigned RGB profile, so its apperance would change depending on the RGB profile assignment.