utils.py

# Copyright 2020 The Flax Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
    This code is created with reference to torchvision/utils.py.

    Modify: torch.tensor -> jax.numpy.DeviceArray

    If you want to know about this file in detail, please visit the original code:
        https://github.com/pytorch/vision/blob/master/torchvision/utils.py
"""
import math
from PIL import Image

import jax
import jax.numpy as jnp


def save_image(ndarray, fp, nrow=8, padding=2, pad_value=0.0, format=None):
    """Make a grid of images and Save it into an image file.
  Args:
    ndarray (array_like): 4D mini-batch images of shape (B x H x W x C)
    fp - A filename(string) or file object
    nrow (int, optional): Number of images displayed in each row of the grid.
      The final grid size is ``(B / nrow, nrow)``. Default: ``8``.
    padding (int, optional): amount of padding. Default: ``2``.
    scale_each (bool, optional): If ``True``, scale each image in the batch of
      images separately rather than the (min, max) over all images. Default: ``False``.
    pad_value (float, optional): Value for the padded pixels. Default: ``0``.
    format(Optional):  If omitted, the format to use is determined from the filename extension.
      If a file object was used instead of a filename, this parameter should always be used.
  """
    if not (isinstance(ndarray, jnp.ndarray) or
        (isinstance(ndarray, list) and all(isinstance(t, jnp.ndarray) for t in ndarray))):
        raise TypeError('array_like of tensors expected, got {}'.format(type(ndarray)))

    ndarray = jnp.asarray(ndarray)

    if ndarray.ndim == 4 and ndarray.shape[-1] == 1:  # single-channel images
        ndarray = jnp.concatenate((ndarray, ndarray, ndarray), -1)

    # make the mini-batch of images into a grid
    nmaps = ndarray.shape[0]
    xmaps = min(nrow, nmaps)
    ymaps = int(math.ceil(float(nmaps) / xmaps))
    height, width = int(ndarray.shape[1] + padding), int(ndarray.shape[2] + padding)
    num_channels = ndarray.shape[3]
    grid = jnp.full((height * ymaps + padding, width * xmaps + padding, num_channels), pad_value).astype(jnp.float32)
    k = 0
    for y in range(ymaps):
      for x in range(xmaps):
        if k >= nmaps:
          break
        grid = jax.ops.index_update(
          grid, jax.ops.index[y * height + padding:(y + 1) * height,
                              x * width + padding:(x + 1) * width],
          ndarray[k])
        k = k + 1

    # Add 0.5 after unnormalizing to [0, 255] to round to nearest integer
    ndarr = jnp.clip(grid * 255.0 + 0.5, 0, 255).astype(jnp.uint8)
    im = Image.fromarray(ndarr.copy())
    im.save(fp, format=format)