matplotlib show many images in single pdf page

Question

Given an image of unknown size as input, the following python script shows it 8 times in a single pdf page:

pdf = PdfPages( './test.pdf' )
gs = gridspec.GridSpec(2, 4)

ax1 = plt.subplot(gs[0])
ax1.imshow( _img )

ax2 = plt.subplot(gs[1])
ax2.imshow( _img )

ax3 = plt.subplot(gs[2])
ax3.imshow( _img )

# so on so forth...

ax8 = plt.subplot(gs[7])
ax8.imshow( _img )

pdf.savefig()
pdf.close()

The input image can have different size (unknown a priori). I tried using the function gs.update(wspace=xxx, hspace=xxx) to change the spacing between the images, hoping that matplotlib would automagically resize and redistribute the images to have least white space possible. However, as you can see below, it didn't work as I expected.

Is there a better way to go to achieve the following?

1. Have images saved with max resolution possible
2. Have less white space possible

Ideally I would like the 8 images to completely will the page size of the pdf (with minimum amount of margin needed).

Answer 1

You were on the right path: hspace and wspace control the spaces between the images. You can also control the margins on the figure with top, bottom, left and right:

import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec
import matplotlib.image as mimage
from matplotlib.backends.backend_pdf import PdfPages

_img = mimage.imread('test.jpg')

pdf = PdfPages( 'test.pdf' )
gs = gridspec.GridSpec(2, 4, top=1., bottom=0., right=1., left=0., hspace=0.,
        wspace=0.)

for g in gs:
    ax = plt.subplot(g)
    ax.imshow(_img)
    ax.set_xticks([])
    ax.set_yticks([])
#    ax.set_aspect('auto')

pdf.savefig()
pdf.close()

Result:

If you want your images to really cover all the available space, then you can set the aspect ratio to auto:

ax.set_aspect('auto')

Result: