[julia-users] Bilinear interpolation of image

[Cristóvão Duarte Sousa]

Hi,

I would like to get the interpolated value at a non-integer point of an 
image.
Using Images.jl and Grid.jl I've tried doing

using Images, TestImages, Grid
img = convert(Image{Gray},testimage("mandrill"))  # for example

img_bi = CoordInterpGrid((1:size(img,1), 1:size(img,2)), img.data, BCnearest
, InterpLinear)
img_bi[12.34, 56.78]

which doesn't work due to img.data being 
an Array{Gray{UfixedBase{Uint8,8}},2} .

On the other hand, this

img_bi = CoordInterpGrid((1:size(img,1), 1:size(img,2)), convert(Matrix{
Float64}, img.data), BCnearest, InterpLinear)

works.
However I'd like to avoid the conversion.

Is there a nice way to do it, or must I implement the bilinear 
interpolation myself?

Thanks,
Cristóvão