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Commit 244daaed authored by Daniel Solomon's avatar Daniel Solomon
Browse files

Change Display White Balance to track the Planckian locus 

Currently when DWB adjusts the display's white point it uses standard
Illuminant D to convert CCT to CIE xy coordinates. This causes a slight
green tint, detectable by some users. Change this behavior to calculate
CIE xy based on the Planckian locus.

Bug: 128712066
Test:
a. Manual, by overriding target DWB CCT and observing resulting target
xy coordinates
b. atest FrameworksServicesTests:ColorDisplayServiceTest, making sure
there are no new failures (existing failures tracked in a separate bug)

Change-Id: I6fa336ee694730df45d5eacceb442aa556b5718e
parent 40e9a201

graphics/java/android/graphics/ColorSpace.java

+39 −0
Original line number Diff line number Diff line
@@ -1808,6 +1808,45 @@ public abstract class ColorSpace { 
        return mul3x3(inverse3x3(matrix), mul3x3Diag(LMS, matrix));

    }



    /**

     * <p>Computes the chromaticity coordinates of a specified correlated color

     * temperature (CCT) on the Planckian locus. The specified CCT must be

     * greater than 0. A meaningful CCT range is [1667, 25000].</p>

     *

     * <p>The transform is computed using the methods in Kang et

     * al., <i>Design of Advanced Color - Temperature Control System for HDTV

     * Applications</i>, Journal of Korean Physical Society 41, 865-871

     * (2002).</p>

     *

     * @param cct The correlated color temperature, in Kelvin

     * @return Corresponding XYZ values

     * @throws IllegalArgumentException If cct is invalid

     *

     * @hide

     */

    @NonNull

    @Size(3)

    public static float[] cctToXyz(@IntRange(from = 1) int cct) {

        if (cct < 1) {

            throw new IllegalArgumentException("Temperature must be greater than 0");

        }



        final float icct = 1e3f / cct;

        final float icct2 = icct * icct;

        final float x = cct <= 4000.0f ?

            0.179910f + 0.8776956f * icct - 0.2343589f * icct2 - 0.2661239f * icct2 * icct :

            0.240390f + 0.2226347f * icct + 2.1070379f * icct2 - 3.0258469f * icct2 * icct;



        final float x2 = x * x;

        final float y = cct <= 2222.0f ?

            -0.20219683f + 2.18555832f * x - 1.34811020f * x2 - 1.1063814f * x2 * x :

            cct <= 4000.0f ?

            -0.16748867f + 2.09137015f * x - 1.37418593f * x2 - 0.9549476f * x2 * x :

            -0.37001483f + 3.75112997f * x - 5.8733867f * x2 + 3.0817580f * x2 * x;



        return xyYToXyz(new float[] {x, y});

    }



    /**

     * <p>Computes the chromaticity coordinates of a CIE series D illuminant

     * from the specified correlated color temperature (CCT). The specified CCT

services/core/java/com/android/server/display/color/ColorDisplayService.java

+1 −1
Original line number Diff line number Diff line
@@ -1417,7 +1417,7 @@ public final class ColorDisplayService extends SystemService { 
                mCurrentColorTemperature = cct;



                // Adapt the display's nominal white point to match the requested CCT value

                mCurrentColorTemperatureXYZ = ColorSpace.cctToIlluminantdXyz(cct);

                mCurrentColorTemperatureXYZ = ColorSpace.cctToXyz(cct);



                mChromaticAdaptationMatrix =

                        ColorSpace.chromaticAdaptation(ColorSpace.Adaptation.BRADFORD,