On Wed, May 30, 2012 at 12:29 AM, Alexander Mikhailov <avm...@yahoo.com> wrote: > I'm playing with some image processing, and not sure how to do > a rather basic thing. > > It actually even applicable to 1D arrays. Suppose we have a > picture, a 2D array of floating point brightness values in the > range from 0 to 1. Suppose we want to superimpose another > array on top of that, with some function for how to merge > brightness from two sources in the same place. For 1D, an > example could be "merge i. 5 with 2 * i. 4 where the second > array is shifted 3 values from the beginning of the first one > and merging values are averaged". I.e. > > 0 1 2 3 4 "merge with shift 3 and averaging" 0 2 4 6 > -> > 0 1 2 1.5 3 4 6
Here you are combining a five element list with a four element list and producing a seven element list. If this were image manipulation, you would be combining layers of different sizes and getting a new layer which was a different size from either of the original sizes. I have never seen any image manipulation application which works like this. So the first step, I think, would be to specify more precisely what it is you want to accomplish. If you just want (average color with transparency) you would need to define a transparent color. The easiest way to implement transparency is to use 0 for transparent, and use an offset when representing other colors so that they are all positive values. In other words if your color range was 0-255, you could add 1 to non-transparent colors (and then subtract 1 when you want to extract their values). If you use this approach, here's averaging two layers, with transparency: (layer1 + layer 2) % layer1 +&* layer2 or layer1 (+ % +&*) layer2 Or, here's averaging a list of n layers (with transparency): (+/ % +/@:*) layers > This could be useful for image manipulations, in 2D case. > > What would be a good way to do that? For example, merge i. 5 5 > with 3 * i. 3 4 shifting the second array 4 _1 from the first > and, say, averaging values on the same places? > > Am I missing some known J patterns? I need to understand what you mean by "merge" before I can comment on that. -- Raul ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
