DataAugmentation
"""
WarpAffine(σ = 0.1) <: ProjectiveTransform
A three-point affine warp calculated by randomly moving 3 corners
of an item. Similar to a random translation, shear and rotation.
"""
struct
WarpAffine
<:
ProjectiveTransform
σ
end
getrandstate
(
::
WarpAffine
)
=
abs
(
rand
(
Int
)
)
function
getprojection
(
tfm
::
WarpAffine
,
bounds
::
Bounds
{
2
}
;
randstate
=
getrandstate
(
tfm
)
)
T
=
Float32
rng
=
Random
.
seed!
(
Random
.
MersenneTwister
(
)
,
randstate
)
scale
=
sqrt
(
prod
(
length
.
(
bounds
.
rs
)
)
)
srcps
=
shuffle
(
rng
,
SVector
{
2
,
T
}
.
(
corners
(
bounds
)
)
)
[
1
:
3
]
offsets
=
rand
(
rng
,
SVector
{
2
,
T
}
,
3
)
offsets
=
map
(
v
->
(
v
.*
(
2
one
(
T
)
)
.-
one
(
T
)
)
.*
convert
(
T
,
scale
*
tfm
.
σ
)
,
offsets
)
return
threepointwarpaffine
(
srcps
,
srcps
.+
offsets
)
endAdapted from
"""
threepointwarpaffine(srcps, dstps)
Calculate an affine [`CoordinateTransformations.LinearMap`](#)
from 3 source points to 3 destination points.
Adapted from [CoordinateTransformations.jl#30](https://github.com/JuliaGeometry/CoordinateTransformations.jl/issues/30#issuecomment-610337378).
"""
function
threepointwarpaffine
(
srcps
::
T
,
dstps
::
T
)
where
{
V
,
T
<:
AbstractArray
{
<:
SVector
{
2
,
V
}
}
}
X
=
vcat
(
hcat
(
dstps
...
)
,
ones
(
1
,
3
)
)
'
Y
=
hcat
(
srcps
...
)
'
c
=
(
X
\
Y
)
'
A
=
SMatrix
{
2
,
2
,
V
}
(
c
[
:
,
1
:
2
]
)
b
=
SVector
{
2
,
V
}
(
c
[
:
,
3
]
)
return
AffineMap
(
A
,
b
)
end
function
corners
(
bounds
::
Bounds
)
(
Tuple
(
x
)
for
x
in
ImageTransformations
.
CornerIterator
(
CartesianIndices
(
bounds
.
rs
)
)
)
end