plot 2D graph

import numpy as np
import matplotlib.pyplot as plt

filename=input("name of the file:")
data = np.genfromtxt(filename, unpack=True, delimiter='\t')
dataname=filename[:-4]

x=data[0,2:]
y=data[1:,0]
xmin=x[0]
xmax=x[-1]
ymin=y[0]
ymax=y[-1]
values = data[1:,2:]
values2=np.rot90(values.T)
values3=(values2-np.min(values2))/(np.max(values2)-np.min(values2))

fig = plt.figure(figsize=(8,8))
ax = fig.gca()
ax.set_xlim(xmin, xmax)
ax.set_ylim(ymin, ymax)
ax.imshow(values3, cmap='jet', extent=[xmin, xmax, ymin, ymax],vmin=0,vmax=0.6)
ax.set_xlabel('emission wavelength [nm]')
ax.set_ylabel('excitation wavelength [nm]')
plt.title('PLE map for ' + dataname)
plt.savefig(dataname+'.png',dpi=150)
plt.show()