从matplotlib savefig删除空格

Question

I'm trying to read in a series of .bmp images and do some linear contrast adjustment based on a tip I got. These images are small, 112x112, and I want to them to come out looking exactly the same except contrast-adjusted. I've tried doing it with matplotlib, but no matter what I do I get white space around the border of the images. Here's the code I'm using:

# Open image and convert to array
oldImage = Image.open(f)
imageArray = np.array(oldImage)

# Preprocessing
vrange = stats.mquantiles(imageArray.flatten(),prob=[0.01,0.99])

# Plot and save
fig = plt.figure()
fig.set_size_inches(1,1)
fig.set_dpi(112)
plt.imshow(imageArray,cmap="gray",interpolation="Nearest",vmin=vrange[0],vmax=vrange[1]);
plt.axis('off')
plt.savefig(f[:-4] + "_adjusted.png", bbox_inches='tight')

Any tips for how to remove the padding? I've done some googling but nothing I've found has worked so far.

Answer 1

You can do thresholding without matplotlib:

import os
from PIL import Image
import numpy as np
import scipy.stats.mstats as mstats

f = os.path.expanduser('~/tmp/image.png')
name, ext = os.path.splitext(f)
out = name+"_adjusted.png"

oldImage = Image.open(f).convert('L')
imageArray = np.array(oldImage)

vmin, vmax = mstats.mquantiles(imageArray.flatten(), prob=[0.01,0.99])

np.clip(imageArray, vmin, vmax, out=imageArray)
imageArray = (imageArray-vmin)*255/(vmax-vmin)
img = Image.fromarray(imageArray.astype('uint8'), 'L')
img.save(out)

This way, you do not have to define a figure size in inches, and a DPI and so forth. You just convert the PIL Image to a numpy array, do some math, and convert back to a PIL Image.

Answer 2

在plt.savefig()之前添加以下行：

plt.subplots_adjust(0,0,1,1,0,0)