a 轴和 b 轴上的 Lab-image 值均超出范围

Question

我把一张彩色图转成Lab-color space，当我显示Lab-image的值时，发现a轴和b轴的像素值是大于128！！而 a 轴和 b 轴上的值应该范围从 -128 到 +128

请问为什么a轴和b轴的值超出范围？

代码:

Log.D(TAG, "main", "labImg.size(): " + labImg.size());
    Log.D(TAG, "main", "dst.dump() \n" + labImg.dump());
    Log.D(TAG, "main", "Luminance:dst.get(0, 9)[0]: " + labImg.get(0, 9)[0]);
    Log.D(TAG, "main", "a-axis:dst.get(0, 9)[1]: " + labImg.get(0, 9)[1]);
    Log.D(TAG, "main", "b-axis:dst.get(0, 9)[2]: " + labImg.get(0, 9)[2]);

输出:

[82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20;
82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20, 82, 207, 20]
3: Debug: MainClass -> main: Luminance:dst.get(0, 9)[0]: 82.0
4: Debug: MainClass -> main: a-axis:dst.get(0, 9)[1]: 207.0
5: Debug: MainClass -> main: b-axis:dst.get(0, 9)[2]: 20.0

Answer 1

L*a*b* 8 位图像的转换结果自动缩放：

RGB <-> CIE Lab* (CV_BGR2Lab, CV_RGB2Lab, CV_Lab2BGR, CV_Lab2RGB).
...
This outputs 0 <= L <= 100, -127 <= a <= 127, -127 <= b <= 127. The values are then converted to the destination data type:

8-bit images
L <- L*255/100, a <- a + 128, b <- b + 128

http://docs.opencv.org/java/2.4.9/org/opencv/imgproc/Imgproc.html#cvtColor(org.opencv.core.Mat,%20org.opencv.core.Mat,%20int)

a 轴和 b 轴上的 Lab-image 值均超出范围

Lab-image values on both of a and b axises exceeds the range

java

opencv

colors

image-processing

javacv