added info on working with masks and rasters

_subsections/chapter04.org

@@ -44,6 +44,25 @@ while you can certainly delete parts of an image and putting something else in i
 1. select the area you want to hide
 2. ALT/OPT + mask button
 
+** compatibility with non raster layer
+
+1. place an image on top of a background
+   - Photoshop->Settings->General->Always Create Smart Objects When Placing
+   - the image is going to be selected as a mask
+
+2. go to the backround layer, select subject the subject
+   - note that "select subject will be highlighed"
+   - [[../_share/media/img/photoshop-beg-piximperfect/lesson4-1.png]]
+
+3. return to the imposed layer and create a negative mask
+   - alt+mask button on layers
+
+4. at this point you can blend the layers if  you like
+   - double click top layer, you'll open to blending options
+   - move the sliders in underlying layer to get what you want
+     - if you hold down the ALT key, and hover over the slider, you can split and drag it
+
+
 * Playlist
 
 #+ATTR_HTML: :class playlist