GPL The GNU General Public License is a form of copyright that is commonly applied to software that the authors wish to distribute for the common good. Paraphrased, it says that the software may be altered and re-distributed as desired but that the original code must also be distributed. For more details on the GPL, see the complete form . Also known as the illumination function . The concept originated in the early 1970s at Xerox's PARC laboratory.
Intermediate values represent increasingly light shades of gray.
A range of accurately known shades of gray printed out for use in calibrating those shades on a display or printer. See aliased response , gridding correction function , cell-averaging , dirty image , and uniform weighting . With judicious choice of C , a high degree of aliasing suppression is possible. See spheroidal function . Since the image plane taper induced by the gridding convolution usually is very severe, the dirty image normally is corrected by pointwise division by the Fourier transform of the convolution function.