From 45cf3100de637ed7e53ebb565fbb840ae1534255 Mon Sep 17 00:00:00 2001
From: KIU Shueng Chuan <nixchuan@gmail.com>
Date: Tue, 13 Apr 2021 03:35:17 +0800
Subject: [PATCH] no need to form a 1d 32-bit lut for array indexing

you can index (y, x) into a lookup table of shape (nentry, 3) or
(nentry, 4) and get an output of shape (y, x, 3) or (y, x, 4)
---
 pyqtgraph/graphicsItems/ImageItem.py          | 22 ++++++-------------
 .../tests/test_ImageItemFormat.py             |  2 +-
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/pyqtgraph/graphicsItems/ImageItem.py b/pyqtgraph/graphicsItems/ImageItem.py
index 681ec1de..f084b093 100644
--- a/pyqtgraph/graphicsItems/ImageItem.py
+++ b/pyqtgraph/graphicsItems/ImageItem.py
@@ -420,7 +420,6 @@ class ImageItem(GraphicsObject):
         # into a single lut for better performance
         scale = None
         levels = self.levels
-        augmented_alpha = False
 
         while True:
             if image.dtype not in (self._xp.ubyte, self._xp.uint16):
@@ -464,18 +463,14 @@ class ImageItem(GraphicsObject):
             # apply the effective lut early for the following types:
             if image.dtype == self._xp.uint16 and (image.ndim == 2 or image.shape[2] == 1):
                 # 1) uint16 mono
-                if lut.ndim == 2:
-                    if lut.shape[1] == 3:   # rgb
-                        # convert rgb lut to rgba so that it is 32-bits
-                        lut = numpy.column_stack([lut, numpy.full(lut.shape[0], 255, dtype=numpy.uint8)])
-                        augmented_alpha = True
-                    if lut.shape[1] == 4:   # rgba
-                        lut = lut.view(numpy.uint32)
-                image = lut.ravel()[image]
+                # before lookup, remove any pesky trailing dimensions
+                if image.ndim == 3 and image.shape[-1] == 1:
+                    image = image.reshape(image.shape[:-1])
+                if lut.ndim == 2 and lut.shape[-1] == 1:
+                    lut = lut.ravel()
+                image = lut[image]
                 lut = None
                 # now both levels and lut are None
-                if image.dtype == numpy.uint32:
-                    image = image.view(numpy.uint8).reshape(image.shape + (4,))
             elif image.ndim == 3 and image.shape[2] == 3:
                 # 2) {uint8, uint16} rgb
                 # for rgb images, the lut will be 1d
@@ -526,10 +521,7 @@ class ImageItem(GraphicsObject):
                 elif image.shape[2] == 3:
                     fmt = QtGui.QImage.Format.Format_RGB888
                 elif image.shape[2] == 4:
-                    if augmented_alpha:
-                        fmt = QtGui.QImage.Format.Format_RGBX8888
-                    else:
-                        fmt = QtGui.QImage.Format.Format_RGBA8888
+                    fmt = QtGui.QImage.Format.Format_RGBA8888
             elif is_indexed8:
                 # levels and/or lut --> lut-only
                 fmt = QtGui.QImage.Format.Format_Indexed8
diff --git a/pyqtgraph/graphicsItems/tests/test_ImageItemFormat.py b/pyqtgraph/graphicsItems/tests/test_ImageItemFormat.py
index 0838c115..09409f36 100644
--- a/pyqtgraph/graphicsItems/tests/test_ImageItemFormat.py
+++ b/pyqtgraph/graphicsItems/tests/test_ImageItemFormat.py
@@ -69,7 +69,7 @@ def test_uint16():
     levels = None
     check_format((h, w), dtype, levels, lut_mono1, Format.Format_Grayscale8)
     check_format((h, w), dtype, levels, lut_mono2, Format.Format_Grayscale8)
-    check_format((h, w), dtype, levels, lut_rgb, Format.Format_RGBX8888)
+    check_format((h, w), dtype, levels, lut_rgb, Format.Format_RGB888)
     check_format((h, w), dtype, levels, lut_rgba, Format.Format_RGBA8888)
 
     levels = [lo, hi]