improve color picking strategy

src/ngio/ngff_meta/fractal_image_meta.py

@@ -7,6 +7,7 @@
 """
 
 from collections.abc import Collection
+from difflib import SequenceMatcher
 from enum import Enum
 from typing import Any, TypeVar
 
@@ -49,15 +50,50 @@ class NgioColors(str, Enum):
     cyan = "00FFFF"
     gray = "808080"
     green = "00FF00"
-    random = "random"
 
-    def random_pick(self) -> "NgioColors":
-        """Pick a random color."""
-        available_colors = [color for color in NgioColors if color != "random"]
-        return available_colors[np.random.randint(0, len(available_colors))]
+    @staticmethod
+    def semi_random_pick(channel_name: str | None = None) -> "NgioColors":
+        """Try to fuzzy match the color to the channel name.
 
-
-def valid_hex_color(v: str) -> str:
+        - If a channel name is given will try to match the channel name to the color.
+        - If name has the paatern 'channel_x' cyclic rotate over a list of colors
+            [cyan, magenta, yellow, green]
+        - If no channel name is given will return a random color.
+        """
+        available_colors = NgioColors._member_names_
+
+        if channel_name is None:
+            # Purely random color
+            color_str = available_colors[np.random.randint(0, len(available_colors))]
+            return NgioColors.__members__[color_str]
+
+        if channel_name.startswith("channel_"):
+            # Rotate over a list of colors
+            defaults_colors = [
+                NgioColors.cyan,
+                NgioColors.magenta,
+                NgioColors.yellow,
+                NgioColors.green,
+            ]
+
+            try:
+                index = int(channel_name.split("_")[-1]) % len(defaults_colors)
+                return defaults_colors[index]
+            except ValueError:
+                # If the name of the channel is something like
+                # channel_dapi this will fail an proceed to the
+                # standard fuzzy match
+                pass
+
+        similarity = {}
+        for color in available_colors:
+            # try to match the color to the channel name
+            similarity[color] = SequenceMatcher(None, channel_name, color).ratio()
+        color_str = max(similarity, key=similarity.get)
+        return NgioColors.__members__[color_str]
+
+
+def valid_hex_color(v: str) -> bool:
     """Validate a hexadecimal color.
 
     Check that `color` is made of exactly six elements which are letters
@@ -70,15 +106,12 @@ def valid_hex_color(v: str) -> str:
      - Tommaso Comparin <[email protected]>
     """
     if len(v) != 6:
-        raise ValueError(f'color must have length 6 (given: "{v}")')
+        return False
     allowed_characters = "abcdefABCDEF0123456789"
     for character in v:
         if character not in allowed_characters:
-            raise ValueError(
-                "color must only include characters from "
-                f'"{allowed_characters}" (given: "{v}")'
-            )
-    return v
+            return False
+    return True
 
 
 class ChannelVisualisation(BaseWithExtraFields):
@@ -95,15 +128,15 @@ class ChannelVisualisation(BaseWithExtraFields):
         active(bool): Whether the channel is active.
     """
 
-    color: str | NgioColors = NgioColors.random
+    color: str | NgioColors | None = Field(default=None, validate_default=True)
     min: int | float = 0
     max: int | float = 65535
     start: int | float = 0
     end: int | float = 65535
     active: bool = True
 
-    @classmethod
     @field_validator("color", mode="after")
+    @classmethod
     def validate_color(cls, value: str | NgioColors) -> str:
         """Color validator.
 
@@ -112,18 +145,22 @@ def validate_color(cls, value: str | NgioColors) -> str:
          - A color name.
          - A NgioColors element.
         """
-        if value in NgioColors:
-            value = NgioColors(value)
-            if value == NgioColors.random:
-                value = value.random_pick()
+        if value is None:
+            return NgioColors.semi_random_pick().value
+        if isinstance(value, str) and valid_hex_color(value):
+            return value
+        elif isinstance(value, str):
+            value_lower = value.lower()
+            return NgioColors.semi_random_pick(value_lower).value
+        elif isinstance(value, NgioColors):
             return value.value
-
-        return valid_hex_color(value)
+        else:
+            raise ValueError("Invalid color value.")
 
     @classmethod
     def lazy_init(
         cls,
-        color: str = "random",
+        color: str | NgioColors | None = None,
         start: int | float | None = None,
         end: int | float | None = None,
         data_type: Any = np.uint16,
@@ -138,7 +175,7 @@ def lazy_init(
         """
         start = start if start is not None else np.iinfo(data_type).min
         end = end if end is not None else np.iinfo(data_type).max
-        return cls(
+        return ChannelVisualisation(
             color=color,
             min=np.iinfo(data_type).min,
             max=np.iinfo(data_type).max,
@@ -166,7 +203,7 @@ def lazy_init(
         cls,
         label: str,
         wavelength_id: str | None = None,
-        color: str = "random",
+        color: str | NgioColors | None = None,
         start: int | float | None = None,
         end: int | float | None = None,
         data_type: Any = np.uint16,
@@ -177,10 +214,16 @@ def lazy_init(
             label(str): The label of the channel.
             wavelength_id(str | None): The wavelength ID of the channel.
             color(str): The color of the channel in hexadecimal format or a color name.
+                If None, the color will be picked based on the label.
             start(int | float | None): The start value of the channel.
             end(int | float | None): The end value of the channel.
             data_type(Any): The data type of the channel.
         """
+        if color is None:
+            # If no color is provided, try to pick a color based on the label
+            # See the NgioColors.semi_random_pick method for more details.
+            color = label
+
         channel_visualization = ChannelVisualisation.lazy_init(
             color=color, start=start, end=end, data_type=data_type
         )

src/ngio/ngff_meta/utils.py

@@ -157,7 +157,9 @@ def create_image_metadata(
             )
 
     if channel_visualization is None:
-        channel_visualization = [ChannelVisualisation() for _ in channel_labels]
+        channel_visualization = [
+            ChannelVisualisation(color=label) for label in channel_labels
+        ]
     else:
         if len(channel_visualization) != len(channel_labels):
             raise ValueError(