Monochrome vs Color (de)Saturation results ?

[bbodine9]

Can someone explain the difference of what I am viewing when using the Monochrome transformation vs moving the color saturation slider all the way to the left and then viewing a different Monochrome result? I am trying to see which will be closer to desaturate in Photoshop as I am trying to replicate a technique which I hope to share later. Thanks!

[jsachs]

By default, Monochrome selects a color filter that effectively extracts the luminance channel from the image - this is a weighted average of the red, green and blue channels that reflects the eye's relative sensitivity to each color.

If you set the filter color in Monochrome to white, the result image is the average of the RGB channels.

Saturation, on the other hand works in either HSV or HSL color space and effectively extract the V or L channel from the image.

I don't know what Photoshop does.