A utility function for TensorFlow that maps a grayscale image to a matplotlib colormap for use with TensorBoard image summaries.

colorize.py

#!/usr/bin/env python
# -*- coding:UTF-8 -*-

# File Name : colorize.py
# Purpose :
# Creation Date : 21-12-2017
# Created By : Jeasine Ma [jeasinema[at]gmail[dot]com]

# ref: https://gist.github.com/jimfleming/c1adfdb0f526465c99409cc143dea97b

import matplotlib
import matplotlib.cm
import cv2
import numpy as np


def colorize(value, factor=1, vmin=None, vmax=None):
    """
    A utility function for TensorFlow that maps a grayscale image to a matplotlib
    colormap for use with TensorBoard image summaries.
    By default it will normalize the input value to the range 0..1 before mapping
    to a grayscale colormap.
    Arguments:
      - value: 2D Tensor of shape [height, width] or 3D Tensor of shape
        [height, width, 1].
      - factor: resize factor, scalar
      - vmin: the minimum value of the range used for normalization.
        (Default: value minimum)
      - vmax: the maximum value of the range used for normalization.
        (Default: value maximum)
    Example usage:
    ```
    output = tf.random_uniform(shape=[256, 256, 1])
    output_color = colorize(output, vmin=0.0, vmax=1.0, cmap='viridis')
    tf.summary.image('output', output_color)
    ```
    Returns a 3D tensor of shape [height, width, 3].
    """

    # normalize
    value = np.sum(value, axis=-1)
    vmin = np.min(value) if vmin is None else vmin
    vmax = np.max(value) if vmax is None else vmax
    value = (value - vmin) / (vmax - vmin)  # vmin..vmax

    value = (value * 255).astype(np.uint8)
    value = cv2.applyColorMap(value, cv2.COLORMAP_PARULA) # or cv2.COLORMAP_JET
    value = cv2.cvtColor(value, cv2.COLOR_BGR2RGB)
    x, y, _ = value.shape
    value = cv2.resize(value, (y * factor, x * factor))

    return value


def colorize_seg(value, factor=1, color='viridis'):
    """
    Arguments:
      - value: 2D Tensor of shape [height, width] or 3D Tensor of shape
        [height, width, 1]., with discrete value, like segmentation gt mask
      - factor: resize factor, scalar
      - color: name of color map, i.e. viridis, jet, plasma
 
    Returns a 3D tensor of shape [height, width, 3].
    """

    # normalize
    n_max, n_min = np.max(value), np.min(value)
    value = (value - n_min)/(n_max-n_min)
    cmap = cm.get_cmap(color)
    value = cmap(value)*255.
    x, y, _ = value.shape
    value = cv2.resize(value, (y * factor, x * factor))

    return value[..., :3]


def tf_colorize(value, factor=1, vmin=None, vmax=None, cmap=None):
    """
    A utility function for TensorFlow that maps a grayscale image to a matplotlib
    colormap for use with TensorBoard image summaries.
    By default it will normalize the input value to the range 0..1 before mapping
    to a grayscale colormap.
    Arguments:
      - value: 2D Tensor of shape [height, width] or 3D Tensor of shape
        [height, width, 1].
      - factor: resize factor, scalar
      - vmin: the minimum value of the range used for normalization.
        (Default: value minimum)
      - vmax: the maximum value of the range used for normalization.
        (Default: value maximum)
      - cmap: a valid cmap named for use with matplotlib's `get_cmap`.
        (Default: 'gray')
    Example usage:
    ```
    output = tf.random_uniform(shape=[256, 256, 1])
    output_color = colorize(output, vmin=0.0, vmax=1.0, cmap='viridis')
    tf.summary.image('output', output_color)
    ```
    Returns a 3D tensor of shape [height, width, 3].
    """
    import tensorflow as tf

    # normalize
    vmin = tf.reduce_min(value) if vmin is None else vmin
    vmax = tf.reduce_max(value) if vmax is None else vmax
    value = (value - vmin) / (vmax - vmin)  # vmin..vmax

    # squeeze last dim if it exists
    value = tf.squeeze(value)

    # quantize
    indices = tf.to_int32(tf.round(value * 255))

    # gather
    cm = matplotlib.cm.get_cmap(cmap if cmap is not None else 'gray')
    colors = tf.constant(cm.colors, dtype=tf.float32)
    value = tf.gather(colors, indices)

    return value