Fix the figure size in style sheet reference

It's better to override absolute sizes in the style sheet. Otherwise,
larger figure images are scaled down due to the limited available width
in the html theme. If not, we still don't get a size relation, but we
also have different magnifications due to the image scaling.

Notes:

- The width (7.4 -> 740px, assuming 100 dpi) is chosen to fit in the
  HTML without scaling.
- The size is chosen to approximately keep the aspect ratio as before.
- The images are now significantly smaller than previously (all former
  images were downscaled). We'll have to verify that the images still
  look good given a lot of information and not much space. If not, we
  need to add a factor.
- All themes use figure.dpi=100, except "classic", which uses 80. Not
  correcting for that is intentional. IMHO "classic" should come out
  smaller to highlight the change in dpi.

Author: timhoffm

examples/style_sheets/style_sheets_reference.py

@@ -109,26 +109,19 @@ def plot_figure(style_label=""):
     # across the different figures.
     prng = np.random.RandomState(96917002)
 
-    # Tweak the figure size to be better suited for a row of numerous plots:
-    # double the width and halve the height. NB: use relative changes because
-    # some styles may have a figure size different from the default one.
-    (fig_width, fig_height) = plt.rcParams['figure.figsize']
-    fig_size = [fig_width * 2, fig_height / 1.75]
-
     fig, axs = plt.subplots(ncols=6, nrows=1, num=style_label,
-                            figsize=fig_size, constrained_layout=True)
+                            figsize=(14.8, 2.7), constrained_layout=True)
 
     # make a suptitle, in the same style for all subfigures,
-    # except those with dark backgrounds, which get a lighter
-    # color:
-    col = np.array([19, 6, 84])/256
-    back = mcolors.rgb_to_hsv(
+    # except those with dark backgrounds, which get a lighter color:
+    background_color = mcolors.rgb_to_hsv(
         mcolors.to_rgb(plt.rcParams['figure.facecolor']))[2]
-    if back < 0.5:
-        col = [0.8, 0.8, 1]
-    fig.suptitle(style_label, x=0.01, fontsize=14, ha='left',
-                 color=col, fontfamily='DejaVu Sans',
-                 fontweight='normal')
+    if background_color < 0.5:
+        title_color = [0.8, 0.8, 1]
+    else:
+        title_color = np.array([19, 6, 84]) / 256
+    fig.suptitle(style_label, x=0.01, ha='left', color=title_color,
+                 fontsize=14, fontfamily='DejaVu Sans', fontweight='normal')
 
     plot_scatter(axs[0], prng)
     plot_image_and_patch(axs[1], prng)