The invention provides, in some aspects, methods and apparatus for signal and/or image processing which perform convolution-based filtering utilizing a graphics processing unit (GPU, also called "graphics card") to compute multiple output pixels at once. This has the advantage of saving memory bandwidth, while leveraging the GPUs vector multiplication and dot product units during the calculation. Related aspects of the invention provide such methods and apparatus in which multiple output pixels are computed simultaneously by using render targets with more than one channel, e.g., an RGBA render target, or multiple render targets, or a combination thereof. By way of non-limiting example, methods and apparatus according to the invention implement convolution on a GPU by executing the steps of defining input image I(x,y) as input texture of size N.sub.x.times.N.sub.y; defining an RGBA render target (output) of size N.sub.x/4.times.N.sub.y; and, for each RGBA output pixel aggregating o(x,y) by (i) reading all input pixels I(x*4+i,y), with i=-4,0,4, and computing o(x,y) for the all four components of the output tuple.