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Sam Skillman committed 4688ae1

Adding cookbook on saving images with different background colors.

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source/cookbook/image_background_colors.py

+from yt.mods import *
+
+# This shows how to save ImageArray objects, such as those returned from 
+# volume renderings, to pngs with varying backgrounds.
+
+# Lets make a fake "rendering" that has 4 channels and looks like a linear
+# gradient from the bottom to top.
+im = np.zeros([64,128,4])
+for i in xrange(im.shape[0]):
+    for k in xrange(im.shape[2]):
+        im[i,:,k] = np.linspace(0.,10.*k, im.shape[1])
+im_arr = ImageArray(im)
+
+# in this case you would have gotten im_arr from something like:
+# im_arr = cam.snapshot() 
+
+# To save it with the default settings, we can just use write_png, where it 
+# rescales the image and uses a black background.
+im_arr.write_png('standard.png')
+ 
+# write_png accepts a background keyword argument that defaults to 'black'.
+# Other choices include:
+# black (0.,0.,0.,1.)
+# white (1.,1.,1.,1.)
+# None  (0.,0.,0.,0.) <-- Transparent!
+# any rgba list/array: [r,g,b,a], bounded by 0..1
+im_arr.write_png('black_bg.png', background='black')
+im_arr.write_png('white_bg.png', background='white')
+im_arr.write_png('green_bg.png', background=[0.,1.,0.,1.])
+im_arr.write_png('transparent_bg.png', background=None)
+
+
+
+
+
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