(PECL imagick 2.0.0)
ImagickPixel::getColorValue — Gets the normalized value of the provided color channel
本函数还未编写文档，仅有参数列表。
Retrieves the value of the color channel specified, as a floating-point number between 0 and 1.
The channel to check, specified as one of the Imagick channel constants.
The value of the channel, as a normalized floating-point number, throwing ImagickPixelException on error.