Photoshop and Corel Photo-Paint have slightly different ways of doing this, but with the same end result. One thing to remember is that for both these programs the white areas apply any effects at full strength and the black, none at all. Grey areas are somewhere between.  

Photoshop. Select all/copy/paste as new layer, click the New Layer Mask icon at the bottom of layers palette. A mask thumbnail will appear to the right of the layer thumbnail. (to view this mask alt+ click the layer thumbnail). Now apply a graduation - or whatever. To view the image again click the layer thumb. Now with the mask layer highlighted apply the desired effect. Finally merge down into the main image.

Corel Photo-Paint. First click the Paint On Mask Tool at the top. Apply your black and white tone, then click the mask tool again. Next make your adjustments or apply any filters, then simply remove. .....the mask (Mask/Remove).

Above, Photp-Paint paint-on mask mode button. Below, Photoshops layer mask.

Below left, the graduated mask through which the effects can be applied, for example lightening in the middle and pixelate on the right.