How to skew an image in Torch

Question

I'm trying to skew an image for input into an NN, but I can't seem to figure out how to do it. There aren't too many libraries which seem to provide what I'm looking for.

Preferably it would work on the type torch.FloatTensor

edit: Actually, the function image.warp looks promising, but the warp_test.lua is not particularly helpful. I am just looking to skew the image in x by a varying amount

Answer 1

Here is a simplistic version:

require 'torch'
require 'image'

local function skew(input, factor)
  local w, h  = input:size(3), input:size(2)
  local y     = torch.range(0, h - 1):view(h, 1):expand(h, w)
  local x     = torch.range(0, w - 1):view(1, w):expand(h, w)
  local field = torch.Tensor(2, h, w)
  field[1]    = y
  field[2]    = torch.add(x, factor or 0, y)
  return image.warp(input, field, "bilinear", false, "pad", 0)
end

local output = skew(image.lena(), 0.25)