I need to visualize a 2D numpy array. I am using pyplot for this. Here's the code:
import cv2 as cv
import numpy as np
from matplotlib import pyplot
img = pyplot.imshow( radiance_val )
#radiance_val is a 2D numpy array of size = ( 512, 512 )
#filled with np.float32 values
pyplot.show()
I am getting the output as expected.
Now my question is, is there any way of converting "img" in the above code from pyplot type to numpy type. I need this so that I can load the visualization as opencv image and perform further processing on it. Im am using python 2.7, 32 bit.
Kindly help
Thank you
EDIT 1: after Thorsten Kranz's solution
import numpy as np
import cv2 as cv
import matplotlib.pyplot as plt
import PIL
from cStringIO import StringIO
frame1 = plt.gca()
frame1.axes.get_xaxis().set_visible(False)
frame1.axes.get_yaxis().set_visible(False)
plt.imshow(np.random.random((10,10)))
buffer_ = StringIO()
plt.savefig( buffer_, format = "png", bbox_inches = 'tight', pad_inches = 0 )
buffer_.seek(0)
image = PIL.Image.open( buffer_ )
ar = np.asarray(image)
cv.imshow( 'a', ar )
cv.waitKey(0)
cv.destroyAllWindows()
Here I am getting a runtime error from MS VC++ runtime library after the program terminates. My better guess is that it is because of the open "buffer_". But I am getting the required output.
EDIT 2: closing the buffer using
buffer_.close()
did not solve the runtime error
FINAL EDIT : SOLUTION
Unless you really need the marker ticks and such,
im._rgba_cache
gives you direct access to the MxNx4 numpy
array that is the color mapped data.
If you just want the color mapped data, you can by pass imshow
entirely and directly color-map the data your self (see guide for picking your color map)
my_cm = maplotlib.cm.get_cmap('Reds')
normed_data = (data - np.min(data)) / (np.max(data) - np.min(data))
mapped_data = my_cm(normed_data)
which will give you back a MxNx4 array mapped between 0
and 1
,
mapped_datau8 = (255 * my_cm(normed_data)).astype('uint8')
or
mapped_data = my_cm(normed_data, bytes=True)
will convert it to unsigned ints.
matplotlib
includes a range of normalization code, see here.
get_cmap
doc and colormap gallery
edit: fixed oversight pointed out at https://stackoverflow.com/a/14880947/380231
Ar you sure you want to convert the return value of the method or the whole plot?
For the latter, you should try:
savefig
See sample below:
import numpy as np
import matplotlib.pyplot as plt
import PIL
from cStringIO import StringIO
plt.imshow(np.random.random((20,20)))
buffer_ = StringIO()
plt.savefig(buffer_, format = "png")
buffer_.seek(0)
image = PIL.Image.open(buffer_)
ar = np.asarray(image)
buffer_.close()
Look into savefig
-*args
and **kwargs
for more options, e.g., dpi, background color, transparency, padding etc.
If you jsut want the color coded image, without axes, labels, etc., I'd still do the same, just use
plt.subplots_adjust(0,0,1,1)
to extend the axes over the whole figure. Take care of the aspect
of you plot, otherwise mpl might shrink your axes again.
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