RGB不能直接轉(zhuǎn)成LAB呈础，需要先轉(zhuǎn)成XYZ量窘，然后在從XYZ轉(zhuǎn)成LAB荐捻。
RGB和XYZ和LAB可以理解為同一類(lèi)顏色空間潘明。
/**
* Convert RGB components to its CIE Lab representative components.
*
* <ul>
* <li>outLab[0] is L [0 ...1)</li>
* <li>outLab[1] is a [-128...127)</li>
* <li>outLab[2] is b [-128...127)</li>
* </ul>
*
* @param r red component value [0..255]
* @param g green component value [0..255]
* @param b blue component value [0..255]
* @param outLab 3-element array which holds the resulting LAB components
*/
public static void RGBToLAB(@IntRange(from = 0x0, to = 0xFF) int r,
@IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b,
@NonNull double[] outLab) {
//outLab就是要輸出的內(nèi)存地址
RGBToXYZ(r, g, b, outLab);
// outLab now contains XYZ
XYZToLAB(outLab[0], outLab[1], outLab[2], outLab);
// outLab now contains LAB representation
}
RGB的數(shù)值范圍都是0~255
這一步就是將RGB歸一化為XYZ：
0 ~ 255歸一化為0 ~ 1
就是i/255（i= [0,255]）
/**
* Convert RGB components to it's CIE XYZ representative components.
*
*
* <p>The resulting XYZ representation will use the D65 illuminant and the CIE
* 2° Standard Observer (1931).</p>
*
* <ul>
* <li>outXyz[0] is X [0 ...95.047)</li>
* <li>outXyz[1] is Y [0...100)</li>
* <li>outXyz[2] is Z [0...108.883)</li>
* </ul>
*
* @param r red component value [0..255]
* @param g green component value [0..255]
* @param b blue component value [0..255]
* @param outXyz 3-element array which holds the resulting XYZ components
*/
public static void RGBToXYZ(@IntRange(from = 0x0, to = 0xFF) int r,
@IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b,
@NonNull double[] outXyz) {
// 要保證RGB三通道不為空
if (outXyz.length != 3) {
throw new IllegalArgumentException("outXyz must have a length of 3.");
}
//下面的可以理解為固定值辐棒，有固有算法
double sr = r / 255.0;
sr = sr < 0.04045 ? sr / 12.92 : Math.pow((sr + 0.055) / 1.055, 2.4);
double sg = g / 255.0;
sg = sg < 0.04045 ? sg / 12.92 : Math.pow((sg + 0.055) / 1.055, 2.4);
double sb = b / 255.0;
sb = sb < 0.04045 ? sb / 12.92 : Math.pow((sb + 0.055) / 1.055, 2.4);
//分別寫(xiě)入RGB三通道內(nèi)存地址
outXyz[0] = 100 * (sr * 0.4124 + sg * 0.3576 + sb * 0.1805);
outXyz[1] = 100 * (sr * 0.2126 + sg * 0.7152 + sb * 0.0722);
outXyz[2] = 100 * (sr * 0.0193 + sg * 0.1192 + sb * 0.9505);
}
然后再?gòu)腦YZ轉(zhuǎn)成LAB病曾，因?yàn)槭侵苯訉?xiě)進(jìn)內(nèi)存的，所以不需要通過(guò)返回值傳遞漾根，而是直接通過(guò)內(nèi)存地址拿值
private static final double XYZ_WHITE_REFERENCE_X = 95.047;
private static final double XYZ_WHITE_REFERENCE_Y = 100;
private static final double XYZ_WHITE_REFERENCE_Z = 108.883;
/**
* Converts a color from CIE XYZ to CIE Lab representation.
*
* <p>This method expects the XYZ representation to use the D65 illuminant and the CIE
* 2° Standard Observer (1931).</p>
*
* <ul>
* <li>outLab[0] is L [0 ...1)</li>
* <li>outLab[1] is a [-128...127)</li>
* <li>outLab[2] is b [-128...127)</li>
* </ul>
*
* @param x X component value [0...95.047)
* @param y Y component value [0...100)
* @param z Z component value [0...108.883)
* @param outLab 3-element array which holds the resulting Lab components
*/
public static void XYZToLAB(@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_X) double x,
@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Y) double y,
@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Z) double z,
@NonNull double[] outLab) {
if (outLab.length != 3) {
throw new IllegalArgumentException("outLab must have a length of 3.");
}
//歸一化組件
x = pivotXyzComponent(x / XYZ_WHITE_REFERENCE_X);
y = pivotXyzComponent(y / XYZ_WHITE_REFERENCE_Y);
z = pivotXyzComponent(z / XYZ_WHITE_REFERENCE_Z);
//寫(xiě)RGB到內(nèi)存地址
outLab[0] = Math.max(0, 116 * y - 16);
outLab[1] = 500 * (x - y);
outLab[2] = 200 * (y - z);
}
csdn上這篇也不錯(cuò)
http://blog.csdn.net/scarecrow_wiscom/article/details/9795715
