How to combine gridspec with plt.subplots() to eliminate space between rows of subplots

The aspect ratio of an imshow plot is automatically set such that pixels in the image are squared. This setting is stronger than any of the subplots_adjust or gridspec settings for spacing. Or in other words you cannot directly control the spacing between subplots if those subplots have their aspect set to "equal".

First obvious solution is to set the image aspect to automatic ax.set_aspect("auto"). This solves the problem of subplot spacing, but distorts the images.

The other option is to adjust the figure margins and the figure size such that the spacing between the subplots is as desired.

Let’s say figh and figw are the figure height and width in inch, and s the subplot width in inch. The margins are bottom, top, left and right (relative to figure size) and the spacings hspace in vertical and wspace in horizontal direction (relative to subplot size). The number of rows is denoted n and the number of columns m. The aspect is the ratio between subplot (image) height and width (aspect = image height / image width).

Then the dimensions can be set via

fig, axes = plt.subplots(nrows=n, ncols=m, figsize=(figwidth, figheight))
plt.subplots_adjust(top=top, bottom=bottom, left=left, right=right, 
                        wspace=wspace, hspace=hspace)

The respective values can be calculated according to:

Or, if the margins are the same:

An example:

import matplotlib.pyplot as plt

image = plt.imread("https://i.stack.imgur.com/9qe6z.png")
aspect = image.shape[0]/float(image.shape[1])
print aspect
n = 2 # number of rows
m = 4 # numberof columns
bottom = 0.1; left=0.05
top=1.-bottom; right = 1.-left
fisasp = (1-bottom-(1-top))/float( 1-left-(1-right) )
#widthspace, relative to subplot size
wspace=0.15  # set to zero for no spacing
hspace=wspace/float(aspect)
#fix the figure height
figheight= 3 # inch
figwidth = (m + (m-1)*wspace)/float((n+(n-1)*hspace)*aspect)*figheight*fisasp

fig, axes = plt.subplots(nrows=n, ncols=m, figsize=(figwidth, figheight))
plt.subplots_adjust(top=top, bottom=bottom, left=left, right=right, 
                    wspace=wspace, hspace=hspace)

for ax in axes.flatten():
    ax.imshow(image)
    ax.set_title("title",fontsize=10)
    ax.axis('off')

plt.show()