I have been working on this for a day and can't get the effect I am looking for. Hopefully I can articulate clearly. The picture should help.
Given the image in Fig. 1 (the image doesn't really matter, it's the effect I am trying to produce) I want to produce highlighted areas - like a diffused spotlight effect - in the general areas indicated by the ovals in Fig. 2.
In Fig. 3 I have created 2 rectangles, applied and positioned 'auto vector mask' (I am still confused about creating masks from 'scratch') to each, set 'blend mode' to multiply, opacity 50%.
In Fig. 4 I have created the larger, center highlight in a similar same manner (the other highlights are hidden here for clarity).
Fig. 5 is the result of all the highlights/masks/objects turned on / visible.
The problem is that I cannot increase/improve the contrast of the center highlight, presumably because it is on top of the 'solid' area of the objects (rectangles) beneath it. I have tried leaving space between the top and bottom rectangles and positioning a middle rectangle with the larger highlight between them (so there is no object underneath, which improves the contrast) but then it does not blend well with the other 2 elements.
That's it in a nutshell. I hope it makes sense!
Instead of using masked objects, draw the ellipses over the area you want to highlight, fill them with white, add a gaussian blur (I used a setting of 30), and then apply the Overlay blend mode. To increase the intensity of the highlights, simply clone the ellipses. You can fine tune the effect of the clones by decreasing or increasing their opacity.
Thanks all. These technique are certainly simpler then what I was doing. I should have inquired sooner!