Photo posterize

[Marrle photo]

In photo, how do I separate the colors of a photo - for example I want to break out the photo into 6 steps of color and I need to see just the red how is this done ? 

Thanks 

[DWright]

To posterise the photo from the Layer menu choose New Adjustment Layer and select Posterise Adjustment then ins the Posterise setting window adjust the posterise levels slider to 6, this can also be done by clicking on the adjustment icon at the bottom of the layer window and selecting Posterise from the adjustment list.