plot several image files in matplotlib subplots - matplotlib

Question

I would like to create a matrix subplot and display each BMP files, from a directory, in a different subplot, but I cannot find the appropriate solution for my problem, could somebody helping me?.
This the code that I have:
import os, sys
from PIL import Image
import matplotlib.pyplot as plt
from glob import glob
bmps = glob('*trace*.bmp')
fig, axes = plt.subplots(3, 3)
for arch in bmps:
i = Image.open(arch)
iar = np.array(i)
for i in range(3):
for j in range(3):
axes[i, j].plot(iar)
plt.subplots_adjust(wspace=0, hspace=0)
plt.show()
I am having the following error after executing:

Answer 1

natively matplotlib only supports PNG images, see http://matplotlib.org/users/image_tutorial.html
then the way is always read the image - plot the image
read image
img1 = mpimg.imread('stinkbug1.png')
img2 = mpimg.imread('stinkbug2.png')
plot image (2 subplots)
plt.figure(1)
plt.subplot(211)
plt.imshow(img1)
plt.subplot(212)
plt.imshow(img2)
plt.show()
follow the tutorial on http://matplotlib.org/users/image_tutorial.html (because of the import libraries)
here is a thread on plotting bmps with matplotlib: Why bmp image displayed as wrong color with plt.imshow of matplotlib on IPython-notebook?

Answer 2

The bmp has three color channels, plus the height and width, giving it a shape of (h,w,3). I believe plotting the image gives you an error because the plot only accepts two dimensions. You could grayscale the image, which would produce a matrix of only two dimensions (h,w).
Without knowing the dimensions of the images, you could do something like this:
for idx, arch in enumerate(bmps):
i = idx % 3 # Get subplot row
j = idx // 3 # Get subplot column
image = Image.open(arch)
iar_shp = np.array(image).shape # Get h,w dimensions
image = image.convert('L') # convert to grayscale
# Load grayscale matrix, reshape to dimensions of color bmp
iar = np.array(image.getdata()).reshape(iar_shp[0], iar_shp[1])
axes[i, j].plot(iar)
plt.subplots_adjust(wspace=0, hspace=0)
plt.show()