Add an OpenCV backend. (#103)

* Add an OpenCV backend.

On conda-forge because all Pillow and OpenCV are built with with
jpegturbo i can't really mesure any difference with the 3 different jpeg
encoders (simplejpeg installed from pip)

* Update

* importorskip

.github/workflows/ci.yml

@@ -75,7 +75,7 @@ jobs:
         shell: bash
         run: |
             python -m pip install --upgrade pip
-            pip install -U jupyter_packaging pytest simplejpeg pillow
+            pip install -U jupyter_packaging pytest simplejpeg pillow opencv-python-headless
             pip install .
             rm -rf ./jupyter_rfb ./build ./egg-info
       - name: Test with pytest

jupyter_rfb/_jpg.py

@@ -99,12 +99,35 @@ def _encode(self, array, quality):
         return f.getvalue()
 
 
+class OpenCVJpegEncoder(JpegEncoder):
+    """A JPEG encoder using the OpenCV library."""
+
+    def __init__(self):
+        import cv2
+
+        self.cv2 = cv2
+
+    def _encode(self, array, quality):
+        if len(array.shape) == 3 and array.shape[2] == 3:
+            # Convert RGB to BGR if needed (assume input is RGB)
+            array = self.cv2.cvtColor(array, self.cv2.COLOR_RGB2BGR)
+
+        # Encode with the specified quality
+        encode_param = [self.cv2.IMWRITE_JPEG_QUALITY, quality]
+        success, encoded_image = self.cv2.imencode(".jpg", array, encode_param)
+        if not success:
+            raise RuntimeError("OpenCV failed to encode image")
+
+        return encoded_image.tobytes()
+
+
 def select_encoder():
     """Select an encoder."""
 
     for cls in [
         SimpleJpegEncoder,  # simplejpeg is fast and lean
         PillowJpegEncoder,  # pillow is commonly available
+        OpenCVJpegEncoder,  # opencv is readily installed in conda environments
     ]:
         try:
             return cls()

tests/test_jpg.py

@@ -1,13 +1,15 @@
 """Test jpg module."""
 
 import numpy as np
+import pytest
 from pytest import raises
 
 from jupyter_rfb._jpg import (
     array2jpg,
     select_encoder,
     SimpleJpegEncoder,
     PillowJpegEncoder,
+    OpenCVJpegEncoder,
 )
 
 
@@ -28,18 +30,28 @@ def test_array2jpg():
 
 def test_simplejpeg_jpeg_encoder():
     """Test the simplejpeg encoder."""
+    pytest.importorskip("simplejpeg")
     encoder = SimpleJpegEncoder()
     _perform_checks(encoder)
     _perform_error_checks(encoder)
 
 
 def test_pillow_jpeg_encoder():
     """Test the pillow encoder."""
+    pytest.importorskip("PIL")
     encoder = PillowJpegEncoder()
     _perform_checks(encoder)
     _perform_error_checks(encoder)
 
 
+def test_opencv_jpeg_encoder():
+    """Test the opencv encoder."""
+    pytest.importorskip("cv2")
+    encoder = OpenCVJpegEncoder()
+    _perform_checks(encoder)
+    _perform_error_checks(encoder)
+
+
 def _perform_checks(encoder):
     # RGB
     im = get_random_im(100, 100, 3)
@@ -111,9 +123,11 @@ def test_select_encoder():
     # Sabotage
     simple_init = SimpleJpegEncoder.__init__
     pillow_init = PillowJpegEncoder.__init__
+    cv2_init = OpenCVJpegEncoder.__init__
     try:
         SimpleJpegEncoder.__init__ = lambda self: raise_importerror()
         PillowJpegEncoder.__init__ = lambda self: raise_importerror()
+        OpenCVJpegEncoder.__init__ = lambda self: raise_importerror()
 
         encoder = select_encoder()
         assert not isinstance(encoder, (SimpleJpegEncoder, PillowJpegEncoder))
@@ -125,3 +139,4 @@ def test_select_encoder():
     finally:
         SimpleJpegEncoder.__init__ = simple_init
         PillowJpegEncoder.__init__ = pillow_init
+        OpenCVJpegEncoder.__init__ = cv2_init