|---|
| [ View source on GitHub](https://github.com/tensorflow/tensorflow/blob/v2.21.0/tensorflow/python/ops/array_ops.py#L6234-L6358) |
Extract `patches` from `images`.
tf.image.extract_patches(
images, sizes, strides, rates, padding, name=None
)
This op collects patches from the input image, as if applying a
convolution. All extracted patches are stacked in the depth (last) dimension
of the output.
Specifically, the op extracts patches of shape `sizes` which are `strides`
apart in the input image. The output is subsampled using the `rates` argument,
in the same manner as "atrous" or "dilated" convolutions.
The result is a 4D tensor which is indexed by batch, row, and column.
`output[i, x, y]` contains a flattened patch of size `sizes[1], sizes[2]`
which is taken from the input starting at
`images[i, x*strides[1], y*strides[2]]`.
Each output patch can be reshaped to `sizes[1], sizes[2], depth`, where
`depth` is `images.shape[3]`.
The output elements are taken from the input at intervals given by the `rate`
argument, as in dilated convolutions.
The `padding` argument has no effect on the size of each patch, it determines
how many patches are extracted. If `VALID`, only patches which are fully
contained in the input image are included. If `SAME`, all patches whose
starting point is inside the input are included, and areas outside the input
default to zero.
#### Example:
n = 10
# images is a 1 x 10 x 10 x 1 array that contains the numbers 1 through 100
images = [[[[x * n + y + 1] for y in range(n)] for x in range(n)]]
# We generate two outputs as follows:
# 1. 3x3 patches with stride length 5
# 2. Same as above, but the rate is increased to 2
tf.image.extract_patches(images=images,
sizes=[1, 3, 3, 1],
strides=[1, 5, 5, 1],
rates=[1, 1, 1, 1],
padding='VALID')
# Yields:
[[[[ 1 2 3 11 12 13 21 22 23]
[ 6 7 8 16 17 18 26 27 28]]
[[51 52 53 61 62 63 71 72 73]
[56 57 58 66 67 68 76 77 78]]]]
If we mark the pixels in the input image which are taken for the output with
`*`, we see the pattern:
* * * 4 5 * * * 9 10
* * * 14 15 * * * 19 20
* * * 24 25 * * * 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
* * * 54 55 * * * 59 60
* * * 64 65 * * * 69 70
* * * 74 75 * * * 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
tf.image.extract_patches(images=images,
sizes=[1, 3, 3, 1],
strides=[1, 5, 5, 1],
rates=[1, 2, 2, 1],
padding='VALID')
# Yields:
[[[[ 1 3 5 21 23 25 41 43 45]
[ 6 8 10 26 28 30 46 48 50]]
[[ 51 53 55 71 73 75 91 93 95]
[ 56 58 60 76 78 80 96 98 100]]]]
We can again draw the effect, this time using the symbols `*`, `x`, `+` and
`o` to distinguish the patches:
* 2 * 4 * x 7 x 9 x
11 12 13 14 15 16 17 18 19 20
* 22 * 24 * x 27 x 29 x
31 32 33 34 35 36 37 38 39 40
* 42 * 44 * x 47 x 49 x
+ 52 + 54 + o 57 o 59 o
61 62 63 64 65 66 67 68 69 70
+ 72 + 74 + o 77 o 79 o
81 82 83 84 85 86 87 88 89 90
+ 92 + 94 + o 97 o 99 o
| ## Args ||
|---|---|
| `images` | A 4-D Tensor with shape `[batch, in_rows, in_cols, depth]`. |
| `sizes` | The size of the extracted patches. Must be `[1, size_rows, size_cols, 1]`. |
| `strides` | A 1-D Tensor of length 4. How far the centers of two consecutive patches are in the images. Must be: `[1, stride_rows, stride_cols, 1]`. |
| `rates` | A 1-D Tensor of length 4. Must be: `[1, rate_rows, rate_cols, 1]`. This is the input stride, specifying how far two consecutive patch samples are in the input. Equivalent to extracting patches with `patch_sizes_eff = patch_sizes + (patch_sizes - 1) * (rates - 1)`, followed by subsampling them spatially by a factor of `rates`. This is equivalent to `rate` in dilated (a.k.a. Atrous) convolutions. |
| `padding` | The type of padding algorithm to use. |
| `name` | A name for the operation (optional). |
| ## Returns ||
|---|---|
| A 4-D Tensor of the same type as the input. ||