Speed up style composition.

The speed up is achieved by have a special case for palettes that have
two entries with the first entry 0 and for conditions where no mask is
required.

Slightly speed up source comparison

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Default to not caching source in notebooks ([#1776](../../pull/1776))
 - Automatically set the JUPYTER_PROXY value ([#1781](../../pull/1781))
 - Add a general channelNames property to tile sources ([#1783](../../pull/1783))
+- Speed up compositing styles ([#1784](../../pull/1784))
 
 ### Changes
 

docs/tilesource_options.rst

@@ -111,7 +111,7 @@ A band definition is an object which can contain the following keys:
 
     - ``band``: the band numpy image in a band stage.
 
-    - ``mask``: a mask numpy image to use when applying the band.
+    - ``mask``: a mask numpy image to use when applying the band.  None for no mask (this is the equivalent of the mask being all True).
 
     - ``palette``: the normalized palette for a band.
 

large_image/tilesource/base.py

@@ -1070,9 +1070,11 @@ def _applyStyle(  # noqa
             if sc.nodata is not None:
                 sc.mask = sc.band != float(sc.nodata)
             else:
-                sc.mask = np.full(image.shape[:2], True)
+                sc.mask = None
             sc.band = (sc.band - sc.min) / delta
             if not sc.clamp:
+                if sc.mask is None:
+                    sc.mask = np.full(image.shape[:2], True)
                 sc.mask = sc.mask & (sc.band >= 0) & (sc.band <= 1)
             sc.band = self._applyStyleFunction(sc.band, sc, 'band')
             # To implement anything other multiply or lighten, we should mimic
@@ -1097,25 +1099,27 @@ def _applyStyle(  # noqa
                     if not channel or np.any(
                             sc.palette[:, channel] != sc.palette[:, channel - 1]):
                         if not sc.discrete:
-                            clrs = np.interp(sc.band, sc.palettebase, sc.palette[:, channel])
+                            if len(sc.palette) == 2 and sc.palette[0, channel] == 0:
+                                clrs = sc.band * sc.palette[1, channel]
+                            else:
+                                clrs = np.interp(sc.band, sc.palettebase, sc.palette[:, channel])
                         else:
                             clrs = sc.palette[
                                 np.floor(sc.band * len(sc.palette)).astype(int).clip(
                                     0, len(sc.palette) - 1), channel]
                 if sc.composite == 'multiply':
                     if eidx:
-                        sc.output[:sc.mask.shape[0], :sc.mask.shape[1], channel] = np.multiply(
-                            sc.output[:sc.mask.shape[0], :sc.mask.shape[1], channel],
-                            np.where(sc.mask, clrs / 255, 1))
+                        sc.output[:clrs.shape[0], :clrs.shape[1], channel] = np.multiply(
+                            sc.output[:clrs.shape[0], :clrs.shape[1], channel],
+                            (clrs / 255) if sc.mask is None else np.where(sc.mask, clrs / 255, 1))
                 else:
                     if not eidx:
-                        sc.output[:sc.mask.shape[0],
-                                  :sc.mask.shape[1],
-                                  channel] = np.where(sc.mask, clrs, 0)
+                        sc.output[:clrs.shape[0], :clrs.shape[1], channel] = (
+                            clrs if sc.mask is None else np.where(sc.mask, clrs, 0))
                     else:
-                        sc.output[:sc.mask.shape[0], :sc.mask.shape[1], channel] = np.maximum(
-                            sc.output[:sc.mask.shape[0], :sc.mask.shape[1], channel],
-                            np.where(sc.mask, clrs, 0))
+                        sc.output[:clrs.shape[0], :clrs.shape[1], channel] = np.maximum(
+                            sc.output[:clrs.shape[0], :clrs.shape[1], channel],
+                            clrs if sc.mask is None else np.where(sc.mask, clrs, 0))
             sc.output = self._applyStyleFunction(sc.output, sc, 'postband')
         if hasattr(sc, 'styleIndex'):
             del sc.styleIndex

test/lisource_compare.py

@@ -146,7 +146,6 @@ def source_compare(sourcePath, opts):  # noqa
     canread = large_image.canReadList(sourcePath, availableSources=sublist)
     if opts.can_read and not len([cr for cr in canread if cr[1]]):
         return None
-    large_image.cache_util.cachesClear()
     slen = max([len(source) for source, _ in canread] + [10])
     sys.stdout.write('Source' + ' ' * (slen - 6))
     sys.stdout.write('  Width Height')
@@ -208,7 +207,8 @@ def source_compare(sourcePath, opts):  # noqa
                     '_geospatial_source', None):
                 continue
             result = results['styles'][-1]['sources'][source] = {}
-            large_image.cache_util.cachesClear()
+            if couldread:
+                large_image.cache_util.cachesClear()
             try:
                 t = time.time()
                 ts = large_image.tilesource.AvailableTileSources[source](sourcePath, **kwargs)