Gri: `mask' command

Gri Commands 1: Introduction 2: Simple example 3: Fancy example 4: Running Gri 5: Programming Gri 6: General Issues 7: X-Y Plots 8: Contour Plots 9: Image Plots 10: Examples 11: Handling Data 12: Gri Commands 13: Gri Extras 14: Evolution of Gri 15: Installing Gri 16: Gri Bugs 17: System Tools 18: Acknowledgments 19: License 20: Newsgroup 21: Concept Index | ## 12.24: The ``mask`' Command
    `mask the image [to {uservalue .u.}|{imagevalue .i.}]'
Examine both the image and the mask pixel by pixel. For any pixels which have a mask value of 1 (which indicates an invalid region of the image), change the image value. If no ``to`' phrase is present, change the image value to 0 in pixel units. If the ``to uservalue .u.`' phrase is present, change the pixel to hold the imagevalue that corresponds to this uservalue (see ``set image range`' command for a discussion of this correspondance). If the ``to imagevalue .i.`', change the pixel to hold that imagevalue (in range 0 to 255 inclusive for 8-bit images).