Merge pull request #1597 from larrybradley/psf-docs

Show data and model with residual image in PSF docs

docs/psf.rst

@@ -268,6 +268,7 @@ and plot it:
 
     import matplotlib.pyplot as plt
     import numpy as np
+    from astropy.visualization import simple_norm
     from photutils.datasets import make_noise_image, make_test_psf_data
     from photutils.detection import DAOStarFinder
     from photutils.psf import IntegratedGaussianPRF, PSFPhotometry
@@ -291,9 +292,16 @@ and plot it:
     phot = psfphot(data, error=error)
 
     resid = psfphot.make_residual_image(data, (25, 25))
-    plt.imshow(resid, origin='lower')
-    plt.title('Residual Image')
-    plt.colorbar()
+
+    fig, ax = plt.subplots(nrows=1, ncols=3, figsize=(15, 5))
+    norm = simple_norm(data, 'sqrt', percent=99)
+    ax[0].imshow(data, origin='lower', norm=norm)
+    ax[1].imshow(data - resid, origin='lower', norm=norm)
+    im = ax[2].imshow(resid, origin='lower')
+    ax[0].set_title('Data')
+    ax[1].set_title('Model')
+    ax[2].set_title('Residual Image')
+    plt.tight_layout()
 
 The residual image looks like noise, indicating good fits to the
 sources.