Store images in memory without alpha

docs/CONTRIBUTING.md

@@ -50,7 +50,7 @@ For image shape and channels, please use `utils.ImageShape` and `utils.ColorChan
 
 ### Image color format and channels
 
-To avoid image shape mismatch issues, and to keep code simpler, we standardize the image color format to BGRA. This should always be done early in the pipeline, so whatever functionality takes care of obtaining an image should also ensure its color format. You can do so with `cv2.cvtColor` (ie: `cv2.cvtColor(image, cv2.COLOR_RGBA2BGRA)` or `cv2.cvtColor(image, cv2.COLOR_BGR2BGRA)`).
+To avoid image shape mismatch issues, reduce memory usage, and to keep code simpler, we standardize the image color format to BGR. This should always be done early in the pipeline, so whatever functionality takes care of obtaining an image should also ensure its color format. You can do so with `cv2.cvtColor` (ie: `cv2.cvtColor(image, cv2.COLOR_RGB2BGR)` or `cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)`). Split Images' transparency is handled by first extracting a binary mask into `AutoSplitImage.mask`.
 
 ### Split-specific setting overrides
 

src/AutoSplit.py

@@ -1087,7 +1087,7 @@ def __update_split_image(self, specific_image: AutoSplitImage | None = None):
             text = "\nor\n".join(self.split_image.texts)
             self.current_split_image.setText(f"Looking for OCR text:\n{text}")
         elif is_valid_image(self.split_image.byte_array):
-            set_preview_image(self.current_split_image, self.split_image.byte_array)
+            set_preview_image(self.current_split_image, self.split_image.get_preview_image())
 
         self.current_image_file_label.setText(self.split_image.filename)
         self.table_current_image_threshold_label.setText(

src/AutoSplitImage.py

@@ -16,7 +16,7 @@
     get_comparison_method_by_index,
 )
 from utils import (
-    BGR_CHANNEL_COUNT,
+    BGRA_CHANNEL_COUNT,
     MAXBYTE,
     TESSERACT_PATH,
     ColorChannel,
@@ -187,16 +187,31 @@ def __read_image_bytes(self, path: str):
                 interpolation=cv2.INTER_NEAREST,
             )
 
-            # Mask based on adaptively resized, nearest neighbor interpolated split image
+            # Mask based on adaptively resized, nearest neighbor interpolated split image.
+            # This must happen before dropping the alpha channel below.
             self.mask = cv2.inRange(image, MASK_LOWER_BOUND, MASK_UPPER_BOUND)
+            image = cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
         else:
             image = cv2.resize(image, COMPARISON_RESIZE, interpolation=cv2.INTER_NEAREST)
-            # Add Alpha channel if missing
-            if image.shape[ImageShape.Channels] == BGR_CHANNEL_COUNT:
-                image = cv2.cvtColor(image, cv2.COLOR_BGR2BGRA)
+            # Captures are standardized to BGR, so drop the alpha channel if present
+            if image.shape[ImageShape.Channels] == BGRA_CHANNEL_COUNT:
+                image = cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
 
         self.byte_array = image
 
+    def get_preview_image(self):
+        """
+        The comparison `byte_array` is stored as BGR, but the preview should
+        show the user the transparency. Re-attach the mask as the alpha channel.
+        """
+        if self.byte_array is None:
+            return None
+        if self.mask is None:
+            return self.byte_array
+        preview = cv2.cvtColor(self.byte_array, cv2.COLOR_BGR2BGRA)
+        preview[:, :, ColorChannel.Alpha] = self.mask
+        return preview
+
     def check_flag(self, flag: int):
         return self.flags & flag == flag
 

src/capture_method/BitBltCaptureMethod.py

@@ -5,6 +5,7 @@
 import ctypes
 from typing import TYPE_CHECKING, override
 
+import cv2
 import numpy as np
 import pywintypes
 import win32con
@@ -84,7 +85,8 @@ def get_frame(self) -> MatLike | None:
         try_delete_dc(compatible_dc)
         win32gui.ReleaseDC(hwnd, window_dc)
         win32gui.DeleteObject(bitmap.GetHandle())
-        return image
+        # The OS hands us a native BGRA buffer; drop the unused alpha
+        return None if image is None else cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
 
     @override
     def recover_window(self, captured_window_title: str):

src/capture_method/CaptureMethodBase.py

@@ -33,7 +33,7 @@ def get_frame(self) -> MatLike | None:  # noqa: PLR6301
         Captures an image of the region for a window matching the given
         parameters of the bounding box.
 
-        @return: The image of the region in the window in BGRA format
+        @return: The image of the region in the window in BGR format
         """
         return None
 

src/capture_method/DesktopDuplicationCaptureMethod.py

@@ -71,4 +71,4 @@ def get_frame(self):
         screenshot = self._desktop_duplication.screenshot((left, top, right, bottom))
         if screenshot is None:
             return None
-        return cv2.cvtColor(screenshot, cv2.COLOR_RGB2BGRA)
+        return cv2.cvtColor(screenshot, cv2.COLOR_RGB2BGR)

src/capture_method/ScrotCaptureMethod.py

@@ -34,7 +34,7 @@ def _scrot_screenshot(x: int, y: int, width: int, height: int):
                 "-z",
                 screenshot_file,
             ))
-            return imread(screenshot_file, cv2.IMREAD_COLOR_RGB)
+            return imread(screenshot_file, cv2.IMREAD_COLOR_BGR)
         except subprocess.CalledProcessError:
             # This can happen when trying to capture a region OOB
             # scrot is rude and prints directly to TTY, no stderr :/
@@ -75,7 +75,8 @@ def get_frame(self):
         )
         if not is_valid_image(image):
             return None
-        return cv2.cvtColor(image, cv2.COLOR_RGB2BGRA)
+        # `imread` with `IMREAD_COLOR_BGR` already gives us BGR
+        return image
 
     @override
     def recover_window(self, captured_window_title: str):

src/capture_method/VideoCaptureDeviceCaptureMethod.py

@@ -143,7 +143,8 @@ def get_frame(self):
             y : y + selection["height"],
             x : x + selection["width"],
         ]
-        self.last_converted_frame = cv2.cvtColor(image, cv2.COLOR_BGR2BGRA)
+        # `cv2.VideoCapture` frames are already BGR
+        self.last_converted_frame = image
         return self.last_converted_frame
 
     @override

src/capture_method/WindowsGraphicsCaptureMethod.py

@@ -7,6 +7,7 @@
 import asyncio
 from typing import TYPE_CHECKING, cast, override
 
+import cv2
 import numpy as np
 import win32api
 import win32gui
@@ -161,6 +162,8 @@ def get_frame(self) -> MatLike | None:
             selection["y"] : selection["y"] + selection["height"],
             selection["x"] : selection["x"] + selection["width"],
         ]
+        # The OS hands us a native BGRA buffer; drop the unused alpha
+        image = cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
         self.last_converted_frame = image
         return image
 

src/capture_method/XcbCaptureMethod.py

@@ -68,7 +68,7 @@ def get_frame(self):
         image = np.array(image)
         if not is_valid_image(image):
             return None
-        return cv2.cvtColor(image, cv2.COLOR_RGB2BGRA)
+        return cv2.cvtColor(image, cv2.COLOR_RGB2BGR)
 
     @override
     def recover_window(self, captured_window_title: str):

src/compare.py

@@ -7,6 +7,7 @@
 import numpy as np
 
 from utils import (
+    BGR_CHANNEL_COUNT,
     BGRA_CHANNEL_COUNT,
     MAXBYTE,
     ColorChannel,
@@ -22,7 +23,7 @@
 CHANNELS = (ColorChannel.Red.value, ColorChannel.Green.value, ColorChannel.Blue.value)
 HISTOGRAM_SIZE = (8, 8, 8)
 RANGES = (0, MAXRANGE, 0, MAXRANGE, 0, MAXRANGE)
-MASK_SIZE_MULTIPLIER = ColorChannel.Alpha * MAXBYTE * MAXBYTE
+MASK_SIZE_MULTIPLIER = BGR_CHANNEL_COUNT * MAXBYTE * MAXBYTE
 MAX_VALUE = 1.0
 CV2_PHASH_SIZE = 8
 

src/region_selection.py

@@ -13,7 +13,7 @@
 import error_messages
 from capture_method import Region
 from utils import (
-    BGR_CHANNEL_COUNT,
+    BGRA_CHANNEL_COUNT,
     MAXBYTE,
     ImageShape,
     auto_split_directory,
@@ -219,9 +219,9 @@ def align_region(autosplit: AutoSplit):
         return
 
     template = imread(template_filename, cv2.IMREAD_UNCHANGED)
-    # Add alpha channel to template if it's missing.
-    if template.shape[ImageShape.Channels] == BGR_CHANNEL_COUNT:
-        template = cv2.cvtColor(template, cv2.COLOR_BGR2BGRA)
+    # Captures are standardized to BGR, so drop the template's alpha channel if present
+    if template.shape[ImageShape.Channels] == BGRA_CHANNEL_COUNT:
+        template = cv2.cvtColor(template, cv2.COLOR_BGRA2BGR)
 
     # Validate template is a valid image file
     if not is_valid_image(template):