--convert-to-jpeg initial version working

osxphotos/imageconverter.py

@@ -0,0 +1,116 @@
+""" ImageConverter class
+    Convert an image to JPEG using CoreImage -- 
+    for example, RAW to JPEG """
+
+# reference: https://stackoverflow.com/questions/59330149/coreimage-ciimage-write-jpg-is-shifting-colors-macos/59334308#59334308
+
+import logging
+import pathlib
+
+import Metal
+import Quartz
+from Cocoa import NSURL
+from Foundation import NSDictionary
+from py import path
+
+# needed to capture system-level stderr
+from wurlitzer import pipes
+
+
+class ImageConverter:
+    """ Convert images to jpeg.  This class is a singleton
+        which will re-use the Core Image CIContext to avoid
+        creating a new context for every conversion. """
+
+    def __new__(cls, *args, **kwargs):
+        """ create new object or return instance of already created singleton """
+        if not hasattr(cls, "instance") or not cls.instance:
+            cls.instance = super().__new__(cls)
+
+        return cls.instance
+
+    def __init__(self):
+        """ return existing singleton or create a new one """
+
+        if hasattr(self, "context"):
+            return
+
+        """ initialize CIContext """
+        context_options = NSDictionary.dictionaryWithDictionary_(
+            {
+                "workingColorSpace": Quartz.CoreGraphics.kCGColorSpaceExtendedSRGB,
+                "workingFormat": Quartz.kCIFormatRGBAh,
+            }
+        )
+        mtldevice = Metal.MTLCreateSystemDefaultDevice()
+        self.context = Quartz.CIContext.contextWithMTLDevice_options_(
+            mtldevice, context_options
+        )
+
+    def write_jpeg(self, input_path, output_path, compression_quality=1.0):
+        """ convert image to jpeg and write image to output_path
+
+        Args:
+            input_path: path to input image (e.g. '/path/to/import/file.CR2') as str or pathlib.Path
+            output_path: path to exported jpeg (e.g. '/path/to/export/file.jpeg') as str or pathlib.Path
+            compression_quality: JPEG compression quality, float in range 0.0 to 1.0; default is 1.0 (best quality)
+
+        Return:
+            True if conversion successful, else False
+
+        Raises:
+            ValueError if compression quality not in range 0.0 to 1.0
+            FileNotFoundError if input_path doesn't exist
+        """
+
+        # accept input_path or output_path as pathlib.Path
+        if not isinstance(input_path, str):
+            input_path = str(input_path)
+
+        if not isinstance(output_path, str):
+            output_path = str(output_path)
+
+        if not pathlib.Path(input_path).is_file():
+            raise FileNotFoundError(f"could not find {input_path}")
+
+        if not (0.0 <= compression_quality <= 1.0):
+            raise ValueError(
+                "illegal value for compression_quality: {compression_quality}"
+            )
+
+        input_url = NSURL.fileURLWithPath_(input_path)
+        output_url = NSURL.fileURLWithPath_(output_path)
+
+        with pipes() as (out, err):
+            # capture stdout and stderr from system calls
+            # otherwise, Quartz.CIImage.imageWithContentsOfURL_
+            # prints to stderr something like:
+            # 2020-09-20 20:55:25.538 python[73042:5650492] Creating client/daemon connection: B8FE995E-3F27-47F4-9FA8-559C615FD774
+            # 2020-09-20 20:55:25.652 python[73042:5650492] Got the query meta data reply for: com.apple.MobileAsset.RawCamera.Camera, response: 0
+            input_image = Quartz.CIImage.imageWithContentsOfURL_(input_url)
+
+        if input_image is None:
+            logging.debug(f"Could not create CIImage for {input_path}")
+            return False
+
+        output_colorspace = (
+            input_image.colorSpace()
+            if input_image.colorSpace()
+            else Quartz.CGColorSpaceCreateWithName(
+                Quartz.CoreGraphics.kCGColorSpaceSRGB
+            )
+        )
+        output_options = NSDictionary.dictionaryWithDictionary_(
+            {"kCGImageDestinationLossyCompressionQuality": compression_quality}
+        )
+        _, error = self.context.writeJPEGRepresentationOfImage_toURL_colorSpace_options_error_(
+            input_image, output_url, output_colorspace, output_options, None
+        )
+        if not error:
+            return True
+        else:
+            logging.debug(
+                "Error converting file {input_path} to jpeg at {output_path}: {error}"
+            )
+            return False
+