Extend invert methods

changelogs/master/20191027_improve_invert.md

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+# Improve Invert #469
+
+* Improved performance of `imgaug.augmenters.arithmetic.invert()` and
+  `imgaug.augmenters.arithmetic.Invert` for `uint8` images.
+* Added function `imgaug.augmenters.arithmetic.invert_()`, an in-place version
+  of `imgaug.augmenters.arithmetic.invert()`.
+* Added parameters `threshold` and `invert_above_threshold` to
+  `imgaug.augmenters.arithmetic.invert()`
+* Added parameters `threshold` and `invert_above_threshold` to
+  `imgaug.augmenters.arithmetic.Invert`.
+* Added function `imgaug.augmenters.arithmetic.solarize()`, a wrapper around
+  `solarize_()`.
+* Added function `imgaug.augmenters.arithmetic.solarize_()`, a wrapper around
+  `invert_()`.
+* Added augmenter `imgaug.augmenters.Solarize`, a wrapper around `Invert`.

checks/check_solarize.py

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+from __future__ import print_function, division, absolute_import
+import imgaug as ia
+import imgaug.augmenters as iaa
+import timeit
+
+
+def main():
+    for size in [64, 128, 256, 512, 1024]:
+        for threshold in [64, 128, 192]:
+            time_iaa = timeit.timeit(
+                "iaa.solarize(image, %d)" % (threshold,),
+                number=1000,
+                setup=(
+                    "import imgaug as ia; "
+                    "import imgaug.augmenters as iaa; "
+                    "image = ia.quokka_square((%d, %d))" % (size, size))
+            )
+            time_pil = timeit.timeit(
+                "np.asarray("
+                "PIL.ImageOps.solarize(PIL.Image.fromarray(image), %d)"
+                ")" % (threshold,),
+                number=1000,
+                setup=(
+                    "import numpy as np; "
+                    "import PIL.Image; "
+                    "import PIL.ImageOps; "
+                    "import imgaug as ia; "
+                    "image = ia.quokka_square((%d, %d))" % (size, size))
+            )
+            print("[size=%04d, thresh=%03d] iaa=%.4f pil=%.4f" % (
+                size, threshold, time_iaa, time_pil))
+
+    image = ia.quokka_square((128, 128))
+    images_aug = iaa.Solarize(1.0)(images=[image] * (5*5))
+    ia.imshow(ia.draw_grid(images_aug))
+
+
+if __name__ == "__main__":
+    main()