photoshop help

[David]

I want to modify an image to simulate higher resolution in the center to show how normal vision works. The best way I think is to fill the image with black pixels that start near the center and increase in density the further you go from the center. But the remaining pixels outside the center are not darkened, and there is no grey or white added to the image. The pixels outside the center just have more and more black pixels overlayed. How would I do this?

I'm using CS5. I'm using the radial gradient tool, with black and white colors, and have tried all the different modes on a blank canvas and existing picture and none of them seem to do it. They all either add white or they darken the image outside the center instead of overlaying black.

[Sypheren]

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