.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "auto_examples/color_exposure/plot_rgb_to_hsv.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_auto_examples_color_exposure_plot_rgb_to_hsv.py>`
        to download the full example code or to run this example in your browser via Binder

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_auto_examples_color_exposure_plot_rgb_to_hsv.py:


==========
RGB to HSV
==========

This example illustrates how RGB to HSV (Hue, Saturation, Value) conversion
[1]_ can be used to facilitate segmentation processes.

Usually, objects in images have distinct colors (hues) and luminosities, so
that these features can be used to separate different areas of the image.
In the RGB representation the hue and the luminosity are expressed as a linear
combination of the R,G,B channels, whereas they correspond to single channels
of the HSV image (the Hue and the Value channels). A simple segmentation of the
image can then be effectively performed by a mere thresholding of the HSV
channels.

.. [1] https://en.wikipedia.org/wiki/HSL_and_HSV

.. GENERATED FROM PYTHON SOURCE LINES 20-26

.. code-block:: Python


    import matplotlib.pyplot as plt

    from skimage import data
    from skimage.color import rgb2hsv








.. GENERATED FROM PYTHON SOURCE LINES 27-28

We first load the RGB image and extract the Hue and Value channels:

.. GENERATED FROM PYTHON SOURCE LINES 28-48

.. code-block:: Python


    rgb_img = data.coffee()
    hsv_img = rgb2hsv(rgb_img)
    hue_img = hsv_img[:, :, 0]
    value_img = hsv_img[:, :, 2]

    fig, (ax0, ax1, ax2) = plt.subplots(ncols=3, figsize=(8, 2))

    ax0.imshow(rgb_img)
    ax0.set_title("RGB image")
    ax0.axis('off')
    ax1.imshow(hue_img, cmap='hsv')
    ax1.set_title("Hue channel")
    ax1.axis('off')
    ax2.imshow(value_img)
    ax2.set_title("Value channel")
    ax2.axis('off')

    fig.tight_layout()




.. image-sg:: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_001.png
   :alt: RGB image, Hue channel, Value channel
   :srcset: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 49-51

We then set a threshold on the Hue channel to separate the cup from the
background:

.. GENERATED FROM PYTHON SOURCE LINES 51-67

.. code-block:: Python


    hue_threshold = 0.04
    binary_img = hue_img > hue_threshold

    fig, (ax0, ax1) = plt.subplots(ncols=2, figsize=(8, 3))

    ax0.hist(hue_img.ravel(), 512)
    ax0.set_title("Histogram of the Hue channel with threshold")
    ax0.axvline(x=hue_threshold, color='r', linestyle='dashed', linewidth=2)
    ax0.set_xbound(0, 0.12)
    ax1.imshow(binary_img)
    ax1.set_title("Hue-thresholded image")
    ax1.axis('off')

    fig.tight_layout()




.. image-sg:: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_002.png
   :alt: Histogram of the Hue channel with threshold, Hue-thresholded image
   :srcset: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_002.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 68-70

We finally perform an additional thresholding on the Value channel to partly
remove the shadow of the cup:

.. GENERATED FROM PYTHON SOURCE LINES 70-82

.. code-block:: Python


    fig, ax0 = plt.subplots(figsize=(4, 3))

    value_threshold = 0.10
    binary_img = (hue_img > hue_threshold) | (value_img < value_threshold)

    ax0.imshow(binary_img)
    ax0.set_title("Hue and value thresholded image")
    ax0.axis('off')

    fig.tight_layout()
    plt.show()



.. image-sg:: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_003.png
   :alt: Hue and value thresholded image
   :srcset: /auto_examples/color_exposure/images/sphx_glr_plot_rgb_to_hsv_003.png
   :class: sphx-glr-single-img






.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 1.372 seconds)


.. _sphx_glr_download_auto_examples_color_exposure_plot_rgb_to_hsv.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: binder-badge

      .. image:: images/binder_badge_logo.svg
        :target: https://mybinder.org/v2/gh/scikit-image/scikit-image/v0.23.2?filepath=notebooks/auto_examples/color_exposure/plot_rgb_to_hsv.ipynb
        :alt: Launch binder
        :width: 150 px

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_rgb_to_hsv.ipynb <plot_rgb_to_hsv.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_rgb_to_hsv.py <plot_rgb_to_hsv.py>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_