[Feature] Command-line script for viewing PNG metadata (#4587)

## What type of PR is this? (check all applicable)

- [X] Feature

## Have you discussed this change with the InvokeAI team?
- [X] No, because it is trivial

      
## Have you updated all relevant documentation?
- [X] Yes -- added a new page listing all the command-line scripts and
their most useful options.

## Description

InvokeAI version 2.3 had a script called `invokeai-metadata` that
accepted a list of png images and printed out JSON-formatted embedded
metadata. I used to use the script for sorting and tagging images
outside of the InvokeAI Web UI framework, and I think people might still
find it useful.

This script stopped working in 3.0 and I didn't notice that until just
now. This PR restores it to a functional state.

## Related Tickets & Documents

None

docs/features/index.md

@@ -51,6 +51,9 @@ Prevent InvokeAI from displaying unwanted racy images.
 ### * [Controlling Logging](LOGGING.md)
 Control how InvokeAI logs status messages.
 
+### * [Command-line Utilities](UTILITIES.md)
+A list of the command-line utilities available with InvokeAI.
+
 <!-- OUT OF DATE
 ### * [Miscellaneous](OTHER.md)
 Run InvokeAI on Google Colab, generate images with repeating patterns,

docs/index.md

@@ -147,6 +147,7 @@ Mac and Linux machines, and runs on GPU cards with as little as 4 GB of RAM.
 
 ### InvokeAI Configuration
 - [Guide to InvokeAI Runtime Settings](features/CONFIGURATION.md)
+- [Database Maintenance and other Command Line Utilities](features/UTILITIES.md)
 
 ## :octicons-log-16: Important Changes Since Version 2.3
 

invokeai/backend/image_util/invoke_metadata.py

@@ -0,0 +1,46 @@
+# Copyright (c) 2023 Lincoln D. Stein and the InvokeAI Development Team
+
+"""Very simple functions to fetch and print metadata from InvokeAI-generated images."""
+
+import json
+import sys
+from pathlib import Path
+from typing import Any, Dict
+
+from PIL import Image
+
+
+def get_invokeai_metadata(image_path: Path) -> Dict[str, Any]:
+    """
+    Retrieve "invokeai_metadata" field from png image.
+
+    :param image_path: Path to the image to read metadata from.
+    May raise:
+      OSError -- image path not found
+      KeyError -- image doesn't contain the metadata field
+    """
+    image: Image = Image.open(image_path)
+    return json.loads(image.text["invokeai_metadata"])
+
+
+def print_invokeai_metadata(image_path: Path):
+    """Pretty-print the metadata."""
+    try:
+        metadata = get_invokeai_metadata(image_path)
+        print(f"{image_path}:\n{json.dumps(metadata, sort_keys=True, indent=4)}")
+    except OSError:
+        print(f"{image_path}:\nNo file found.")
+    except KeyError:
+        print(f"{image_path}:\nNo metadata found.")
+    print()
+
+
+def main():
+    """Run the command-line utility."""
+    image_paths = sys.argv[1:]
+    if not image_paths:
+        print(f"Usage: {Path(sys.argv[0]).name} image1 image2 image3 ...")
+        print("\nPretty-print InvokeAI image metadata from the listed png files.")
+        sys.exit(-1)
+    for img in image_paths:
+        print_invokeai_metadata(img)

pyproject.toml

@@ -142,7 +142,7 @@ dependencies = [
 "invokeai-model-install" = "invokeai.frontend.install.model_install:main"
 "invokeai-migrate3" = "invokeai.backend.install.migrate_to_3:main"
 "invokeai-update" = "invokeai.frontend.install.invokeai_update:main"
-"invokeai-metadata" = "invokeai.frontend.CLI.sd_metadata:print_metadata"
+"invokeai-metadata" = "invokeai.backend.image_util.invoke_metadata:main"
 "invokeai-node-cli" = "invokeai.app.cli_app:invoke_cli"
 "invokeai-node-web" = "invokeai.app.api_app:invoke_api"
 "invokeai-import-images" = "invokeai.frontend.install.import_images:main"