Color picker - Lab format: use roundoff optional #13603 by ruthiesun · Pull Request #42986 · microsoft/PowerToys

ruthiesun · 2025-10-27T04:24:59Z

Summary of the Pull Request

The default CIELab format rounds the values to two decimal places, which is a degree of precision that isn't always needed. This PR adds an optional formatting character (i) to the three CIELab format parameters, which rounds the value to the nearest integer.

PR Checklist

Detailed Description of the Pull Request / Additional comments

In the case where a or b get rounded to -0 (e.g. -0.0001 rounds to -0), the negative sign gets removed. However, I noticed during testing that the default format (rounding to two decimal places) retains the negative sign in these situations (see third screenshot). I can a) revert to keeping the -0 for the new rounding behavior, b) change -0 to 0 for other rounded values, or c) leave it as-is. Also open to suggestions.

I can update the docs as well, if we're happy with the approach.

Validation Steps Performed

Settings: Can change the default CIELab format to display rounded values
Settings: Can create a custom format with rounded CIELab values
Color Picker: Rounded values are displayed when hovering and as a saved color

ruthiesun · 2025-10-27T04:30:19Z

@microsoft-github-policy-service agree

niels9001 · 2026-02-24T09:09:30Z

/azp run

azure-pipelines · 2026-02-24T09:09:40Z

Azure Pipelines successfully started running 1 pipeline(s).

…lab-format

vanzue · 2026-02-25T06:06:34Z

/azp run

azure-pipelines · 2026-02-25T06:06:43Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Adds an optional integer-rounding formatter for CIELab components in Color Picker formats, and updates the Settings UI help so users can discover/use the new formatter.

Changes:

Extends ColorFormatHelper to support an i format suffix for %Lc/%Ca/%Cb to round CIELab values to whole numbers.
Updates the Settings UI Color Format Editor to show the new CIELab-specific formatter option.
Updates localized help strings to describe CIELab formatting options.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/settings-ui/Settings.UI/Strings/en-us/Resources.resw	Updates help text and adds a new localized description for integer rounding.
src/settings-ui/Settings.UI/SettingsXAML/Controls/ColorFormatEditor.xaml.cs	Populates a new CIELab formatter list (adds `i`) and renames the RGBA formatter list control.
src/settings-ui/Settings.UI/SettingsXAML/Controls/ColorFormatEditor.xaml	Adds UI elements to display the CIELab formatter list and adjusts helpline text blocks accordingly.
src/common/ManagedCommon/ColorFormatHelper.cs	Implements the `i` formatter behavior for CIELab output via a shared formatting helper.

Copilot · 2026-02-25T06:14:26Z

src/common/ManagedCommon/ColorFormatHelper.cs

+                case 'i':
+                    double roundedColorPercentValue = Math.Round(colorPercentValue);
+                    if (roundedColorPercentValue == 0)
+                    {


Math.Round(colorPercentValue) uses midpoint rounding-to-even by default. For a user-facing “rounded to nearest integer” option this can be surprising for *.5 values (e.g., 74.5 -> 74). Consider explicitly choosing a midpoint mode (commonly AwayFromZero) so rounding matches typical expectations.

Should be ok in this scenario

Copilot · 2026-02-25T06:14:27Z

src/common/ManagedCommon/ColorFormatHelper.cs

+        private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)
+        {
+            switch (paramFormat)
+            {


The new i formatter for %Lc/%Ca/%Cb is behavior-changing but doesn’t appear to have unit coverage. There are existing ColorPicker unit tests for default format output; please add tests that assert integer rounding (and edge cases like negative values near 0) to prevent regressions.

Copilot · 2026-02-25T06:14:27Z

src/common/ManagedCommon/ColorFormatHelper.cs

+        private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)
+        {
+            switch (paramFormat)
+            {
+                case 'i':
+                    double roundedColorPercentValue = Math.Round(colorPercentValue);
+                    if (roundedColorPercentValue == 0)
+                    {
+                        // convert -0 to 0
+                        roundedColorPercentValue = 0.0;
+                    }
+
+                    return roundedColorPercentValue.ToString(CultureInfo.InvariantCulture);
+                default:
+                    return Math.Round(colorPercentValue, defaultDecimalDigits).ToString(CultureInfo.InvariantCulture);
+            }
+        }
+


ColorPercentFormatted is now used for CIELab L/a/b values but doesn’t actually apply a percent transformation (no *100, no % sign). Consider renaming the helper to reflect what it does (round/format a double) to avoid confusing future callers.

Suggested change

private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)

{

switch (paramFormat)

{

case 'i':

double roundedColorPercentValue = Math.Round(colorPercentValue);

if (roundedColorPercentValue == 0)

{

// convert -0 to 0

roundedColorPercentValue = 0.0;

}

return roundedColorPercentValue.ToString(CultureInfo.InvariantCulture);

default:

return Math.Round(colorPercentValue, defaultDecimalDigits).ToString(CultureInfo.InvariantCulture);

}

}

/// <summary>

/// Formats a color component value according to the specified format.

/// This helper performs rounding only and does not apply any percent transformation

/// (no multiplication by 100 and no percent sign is added).

/// </summary>

private static string FormatColorComponent(double value, char paramFormat, int defaultDecimalDigits)

{

switch (paramFormat)

{

case 'i':

double roundedValue = Math.Round(value);

if (roundedValue == 0)

{

// convert -0 to 0

roundedValue = 0.0;

}

return roundedValue.ToString(CultureInfo.InvariantCulture);

default:

return Math.Round(value, defaultDecimalDigits).ToString(CultureInfo.InvariantCulture);

}

}

/// <summary>

/// Formats a color value that was historically treated as a "percent" value.

/// This method does not apply a percent transformation; it simply rounds and formats

/// the provided value. Use <see cref="FormatColorComponent"/> for new code.

/// </summary>

[Obsolete("ColorPercentFormatted does not apply a percent transformation. Use FormatColorComponent instead.")]

private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)

{

return FormatColorComponent(colorPercentValue, paramFormat, defaultDecimalDigits);

}

Copilot · 2026-02-25T06:14:27Z

src/settings-ui/Settings.UI/Strings/en-us/Resources.resw

+    <value>rounded to the nearest integer</value>
+  </data>
+  <data name="ColorFormatEditorHelpline4.Text" xml:space="preserve">
    <value>Example:  %ReX means red value in hex uppercase two digits format.</value>


The updated help text introduces a Lab-specific formatter (i), but the only example shown is still %ReX (RGB). Consider adding a Lab example (e.g., how to use i with %Lc/%Ca/%Cb) and/or stating the default (two decimal places) when no formatter is provided, so the new option is discoverable.

Suggested change

<value>Example: %ReX means red value in hex uppercase two digits format.</value>

<value>Example: %ReX means red value in hex uppercase two digits format. %Li means lightness value formatted as an integer using the Lab-specific 'i' formatter. When no formatter is provided (for example, %L, %Ca or %Cb), the value is shown with two decimal places by default.</value>

vanzue

Verified locally

drms · 2026-02-28T20:23:11Z

Looking forward to the implementation released in next PT version. Thanks

Color picker - Lab format: use roundoff optional microsoft#13603

733de04

niels9001 added the In for .97 label Jan 8, 2026

niels9001 added 0.98 and removed In for .97 labels Feb 24, 2026

vanzue added 2 commits February 25, 2026 13:41

Fix XAML formatting in ColorFormatEditor

fc76dd3

Merge remote-tracking branch 'origin/main' into ruthiesun/rounded-cie…

64977a7

…lab-format

vanzue requested a review from Copilot February 25, 2026 06:08

Copilot started reviewing on behalf of vanzue February 25, 2026 06:09 View session

Copilot AI reviewed Feb 25, 2026

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vanzue approved these changes Feb 25, 2026

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vanzue enabled auto-merge (squash) February 25, 2026 06:48

niels9001 self-requested a review February 27, 2026 22:12

niels9001 approved these changes Feb 27, 2026

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vanzue merged commit 3e1b07f into microsoft:main Feb 27, 2026
15 checks passed

zateutsch added this to the PowerToys 0.98 milestone Mar 4, 2026

zateutsch added the Product-Color Picker All things around the Color Picker utility label Mar 5, 2026

-        private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)
-        {
-            switch (paramFormat)
-            {
-                case 'i':
-                    double roundedColorPercentValue = Math.Round(colorPercentValue);
-                    if (roundedColorPercentValue == 0)
-                    {
-                        // convert -0 to 0
-                        roundedColorPercentValue = 0.0;
-                    }
-                    return roundedColorPercentValue.ToString(CultureInfo.InvariantCulture);
-                default:
-                    return Math.Round(colorPercentValue, defaultDecimalDigits).ToString(CultureInfo.InvariantCulture);
-            }
-        }
+        /// <summary>
+        /// Formats a color component value according to the specified format.
+        /// This helper performs rounding only and does not apply any percent transformation
+        /// (no multiplication by 100 and no percent sign is added).
+        /// </summary>
+        private static string FormatColorComponent(double value, char paramFormat, int defaultDecimalDigits)
+        {
+            switch (paramFormat)
+            {
+                case 'i':
+                    double roundedValue = Math.Round(value);
+                    if (roundedValue == 0)
+                    {
+                        // convert -0 to 0
+                        roundedValue = 0.0;
+                    }
+                    return roundedValue.ToString(CultureInfo.InvariantCulture);
+                default:
+                    return Math.Round(value, defaultDecimalDigits).ToString(CultureInfo.InvariantCulture);
+            }
+        }
+        /// <summary>
+        /// Formats a color value that was historically treated as a "percent" value.
+        /// This method does not apply a percent transformation; it simply rounds and formats
+        /// the provided value. Use <see cref="FormatColorComponent"/> for new code.
+        /// </summary>
+        [Obsolete("ColorPercentFormatted does not apply a percent transformation. Use FormatColorComponent instead.")]
+        private static string ColorPercentFormatted(double colorPercentValue, char paramFormat, int defaultDecimalDigits)
+        {
+            return FormatColorComponent(colorPercentValue, paramFormat, defaultDecimalDigits);
+        }

	<value>Example: %ReX means red value in hex uppercase two digits format.</value>
	<value>Example: %ReX means red value in hex uppercase two digits format. %Li means lightness value formatted as an integer using the Lab-specific 'i' formatter. When no formatter is provided (for example, %L, %Ca or %Cb), the value is shown with two decimal places by default.</value>

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ruthiesun commented Oct 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary of the Pull Request

PR Checklist

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ruthiesun commented Oct 27, 2025

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ruthiesun commented Oct 27, 2025 •

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