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SpatialGlimpse.lua
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SpatialGlimpse.lua
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------------------------------------------------------------------------
--[[ SpatialGlimpse ]]--
-- Ref A.: http://papers.nips.cc/paper/5542-recurrent-models-of-visual-attention.pdf
-- a glimpse is the concatenation of down-scaled cropped images of
-- increasing scale around a given location in a given image.
-- input is a pair of Tensors: {image, location}
-- locations are x,y coordinates of the center of cropped patches.
-- Coordinates are between -1,-1 (top-left) and 1,1 (bottom right)
-- output is a batch of glimpses taken in image at location (x,y)
-- glimpse size is {height, width}, or width only if square-shaped
-- depth is number of patches to crop per glimpse (one patch per scale)
-- Each successive patch is scale x size of the previous patch
------------------------------------------------------------------------
local SpatialGlimpse, parent = torch.class("nn.SpatialGlimpse", "nn.Module")
function SpatialGlimpse:__init(size, depth, scale)
nn.require('nnx')
if torch.type(size)=='table' then
self.height = size[1]
self.width = size[2]
else
self.width = size
self.height = size
end
self.depth = depth or 3
self.scale = scale or 2
assert(torch.type(self.width) == 'number')
assert(torch.type(self.height) == 'number')
assert(torch.type(self.depth) == 'number')
assert(torch.type(self.scale) == 'number')
parent.__init(self)
self.gradInput = {torch.Tensor(), torch.Tensor()}
if self.scale == 2 then
self.module = nn.SpatialAveragePooling(2,2,2,2)
else
self.module = nn.SpatialReSampling{oheight=self.height,owidth=self.width}
end
self.modules = {self.module}
end
-- a bandwidth limited sensor which focuses on a location.
-- locations index the x,y coord of the center of the output glimpse
function SpatialGlimpse:updateOutput(inputTable)
nn.require('nnx')
assert(torch.type(inputTable) == 'table')
assert(#inputTable >= 2)
local input, location = unpack(inputTable)
input, location = self:toBatch(input, 3), self:toBatch(location, 1)
assert(input:dim() == 4 and location:dim() == 2)
self.output:resize(input:size(1), self.depth, input:size(2), self.height, self.width)
self._crop = self._crop or self.output.new()
self._pad = self._pad or input.new()
for sampleIdx=1,self.output:size(1) do
local outputSample = self.output[sampleIdx]
local inputSample = input[sampleIdx]
local yx = location[sampleIdx]
-- (-1,-1) top left corner, (1,1) bottom right corner of image
local y, x = yx:select(1,1), yx:select(1,2)
-- (0,0), (1,1)
y, x = (y+1)/2, (x+1)/2
-- for each depth of glimpse : pad, crop, downscale
local glimpseWidth = math.floor(self.width)
local glimpseHeight = math.floor(self.height)
for depth=1,self.depth do
local dst = outputSample[depth]
if depth > 1 then
glimpseWidth = math.floor(glimpseWidth*self.scale)
glimpseHeight = math.floor(glimpseHeight*self.scale)
end
-- add zero padding (glimpse could be partially out of bounds)
local padWidth = math.floor((glimpseWidth-1)/2)
local padHeight = math.floor((glimpseHeight-1)/2)
self._pad:resize(input:size(2), input:size(3)+padHeight*2, input:size(4)+padWidth*2):zero()
local center = self._pad:narrow(2,padHeight+1,input:size(3)):narrow(3,padWidth+1,input:size(4))
center:copy(inputSample)
-- crop it
local h, w = self._pad:size(2)-glimpseHeight, self._pad:size(3)-glimpseWidth
local y, x = math.floor(math.min(h,math.max(0,y*h))), math.floor(math.min(w,math.max(0,x*w)))
if depth == 1 then
dst:copy(self._pad:narrow(2,y+1,glimpseHeight):narrow(3,x+1,glimpseWidth))
else
self._crop:resize(input:size(2), glimpseHeight, glimpseWidth)
self._crop:copy(self._pad:narrow(2,y+1,glimpseHeight):narrow(3,x+1,glimpseWidth))
if torch.type(self.module) == 'nn.SpatialAveragePooling' then
local poolWidth = glimpseWidth/self.width
assert(poolWidth % 2 == 0)
local poolHeight = glimpseHeight/self.height
assert(poolHeight % 2 == 0)
self.module.kW = poolWidth
self.module.kH = poolHeight
self.module.dW = poolWidth
self.module.dH = poolHeight
end
dst:copy(self.module:updateOutput(self._crop))
end
end
end
self.output:resize(input:size(1), self.depth*input:size(2), self.height, self.width)
self.output = self:fromBatch(self.output, 1)
return self.output
end
function SpatialGlimpse:updateGradInput(inputTable, gradOutput)
local input, location = unpack(inputTable)
if #self.gradInput ~= 2 then
self.gradInput = {input.new(), input.new()}
end
local gradInput, gradLocation = unpack(self.gradInput)
input, location = self:toBatch(input, 3), self:toBatch(location, 1)
gradOutput = self:toBatch(gradOutput, 3)
gradInput:resizeAs(input):zero()
gradLocation:resizeAs(location):zero() -- no backprop through location
gradOutput = gradOutput:view(input:size(1), self.depth, input:size(2), self.height, self.width)
for sampleIdx=1,gradOutput:size(1) do
local gradOutputSample = gradOutput[sampleIdx]
local gradInputSample = gradInput[sampleIdx]
local yx = location[sampleIdx] -- height, width
-- (-1,-1) top left corner, (1,1) bottom right corner of image
local y, x = yx:select(1,1), yx:select(1,2)
-- (0,0), (1,1)
y, x = (y+1)/2, (x+1)/2
-- for each depth of glimpse : pad, crop, downscale
local glimpseWidth = math.floor(self.width)
local glimpseHeight = math.floor(self.height)
for depth=1,self.depth do
local src = gradOutputSample[depth]
if depth > 1 then
glimpseWidth = math.floor(glimpseWidth*self.scale)
glimpseHeight = math.floor(glimpseHeight*self.scale)
end
-- add zero padding (glimpse could be partially out of bounds)
local padWidth = math.floor((glimpseWidth-1)/2)
local padHeight = math.floor((glimpseHeight-1)/2)
self._pad:resize(input:size(2), input:size(3)+padHeight*2, input:size(4)+padWidth*2):zero()
local h, w = self._pad:size(2)-glimpseHeight, self._pad:size(3)-glimpseWidth
local y, x = math.floor(math.min(h,math.max(0,y*h))), math.floor(math.min(w,math.max(0,x*w)))
local pad = self._pad:narrow(2, y+1, glimpseHeight):narrow(3, x+1, glimpseWidth)
-- upscale glimpse for different depths
if depth == 1 then
pad:copy(src)
else
self._crop:resize(input:size(2), glimpseHeight, glimpseWidth)
if torch.type(self.module) == 'nn.SpatialAveragePooling' then
local poolWidth = glimpseWidth/self.width
assert(poolWidth % 2 == 0)
local poolHeight = glimpseHeight/self.height
assert(poolHeight % 2 == 0)
self.module.kW = poolWidth
self.module.kH = poolHeight
self.module.dW = poolWidth
self.module.dH = poolHeight
end
pad:copy(self.module:updateGradInput(self._crop, src))
end
-- copy into gradInput tensor (excluding padding)
gradInputSample:add(self._pad:narrow(2, padHeight+1, input:size(3)):narrow(3, padWidth+1, input:size(4)))
end
end
self.gradInput[1] = self:fromBatch(gradInput, 1)
self.gradInput[2] = self:fromBatch(gradLocation, 1)
return self.gradInput
end