Re: How to downsample a image matrix using left and right

*To*: mathgroup at smc.vnet.net*Subject*: [mg100888] Re: How to downsample a image matrix using left and right*From*: Ray Koopman <koopman at sfu.ca>*Date*: Wed, 17 Jun 2009 04:45:02 -0400 (EDT)*References*: <h19i7r$p7g$1@smc.vnet.net>

On Jun 16, 6:51 pm, tenveer <ten.v... at gmail.com> wrote: > HI all > > i am just stuck with a unique problem ... > > What i want is to downsample a matrix (image matrix) using two left > and right matrices.... > e.g if i have a 100 by 100 image matrix X what i want is to downsample > X to 25 by 25 matrix Y using two downsampling matrices U and V which > are on left and right respectively i.e Y=U*X*V > > than what will the contents of the U and V matrices. > > Any help will be appreciated If you just want to take means then you can use U = Flatten /@ (IdentityMatrix[25] /. {1 -> {.25,.25,.25,.25}, 0 -> {0,0,0,0}}) and V = Transpose@U. However, you can also get U.X.Transpose@U as Nest[ Transpose[Mean/@Partition[#,4]]&, X, 2].