This method uses the lighness channel of the Lab colorspace to do the black and white conversion.
Warning: This method changes the color mode of your image to Lab. Be sure to change the mode back to RGB. Otherwise some enhancements, such as toning, may not work
This method takes advantage of the lightness channel of the. The first step is to convert the image from RGB to Lab color. Then isolate the lightness channel and discard the a and b channels. The final step is to convert back to RGB.
This is a color chart with the six primary and secondary colors, along with their RGB values. For an explanation of this chart see RGB Theory.
Here's the color chart converte with this method along with its grayscale values:
This conversion forms the first step in the Gorman Method.