How to remove axis, legends, and white padding

ghz 3months ago ⋅ 39 views

I would like to apply colormap to an image, and write the resulting image, without using axes, labels, titles, or anything automatically added by matplotlib. Here is what I did:

def make_image(inputname,outputname):
    data = mpimg.imread(inputname)[:,:,0]
    fig = plt.imshow(data)
    fig.set_cmap('hot')
    fig.axes.get_xaxis().set_visible(False)
    fig.axes.get_yaxis().set_visible(False)
    plt.savefig(outputname)

It successfully removes the axis of the figure, but the figure saved, presents a white padding, and a frame around the actual image.

How can I remove them (at least the white padding)?

Answers

To save the image without any padding or additional frame in matplotlib, you can use the bbox_inches='tight' option in the plt.savefig() call and pad_inches=0 to remove the padding.

Also, to make sure that only the image is saved (without any axes, labels, or titles), it's better to use plt.axis('off') to fully hide axes, and plt.gcf().set_size_inches to control the figure size.

Here's how you can modify your code:

import matplotlib.pyplot as plt
import matplotlib.image as mpimg

def make_image(inputname, outputname):
    data = mpimg.imread(inputname)[:, :, 0]  # Read the image and take the first channel
    plt.imshow(data, cmap='hot')  # Apply colormap
    plt.axis('off')  # Hide axes
    plt.gcf().set_size_inches((data.shape[1] / 100.0, data.shape[0] / 100.0))  # Set figure size based on image dimensions
    plt.subplots_adjust(left=0, right=1, top=1, bottom=0)  # Remove padding between image and edges
    plt.savefig(outputname, bbox_inches='tight', pad_inches=0)  # Save without padding
    plt.close()  # Close the figure to free memory

Explanation:

  • plt.axis('off'): This hides all axes, labels, and ticks.
  • plt.gcf().set_size_inches(): Adjusts the size of the figure to match the dimensions of the image.
  • plt.subplots_adjust(): Sets the margins to zero to prevent any padding.
  • bbox_inches='tight', pad_inches=0: Ensures the saved image has no extra padding or borders.

This will save the image without the white padding and frame.

#python