[Mohamed Emad (TheGeekyM)]

Summary

ImageConverter now calls the shared llm_caption helper in converters/_llm_caption.py instead of its own private copy, _get_llm_description. PptxConverter already uses that helper. The private method and the imports only it needed are deleted. Behaviour stays the same: errors from the client still propagate, and a None caption still leaves the description out.

Motivation

There were two copies of the image-captioning request code. ImageConverter._get_llm_description and llm_caption in _llm_caption.py were the same line for line. Both used the same default prompt ("Write a detailed caption for this image."), resolved the content type the same way (mimetype, then mimetypes.guess_type on the extension, then application/octet-stream), saved and restored the stream position around the base64 read, and sent the same OpenAI-style message. PptxConverter (_pptx_converter.py:186) already called llm_caption. Only the image converter still had its own copy.

The duplication was already known. tests/test_module_misc.py had a TODO saying the LLM parameter test "may only use one test after the llm caption method duplicate has been removed", with a link to #1254.

Keeping two copies means any change to the request has to be made twice: the default prompt, how content types are handled, the message format, or support for a different client. If someone misses one, images and PPTX slides start getting different captions. This affects anyone who passes llm_client/llm_model to MarkItDown, and it is the main thing standing in the way of the larger goal of unifying the vision-caption code paths.

What changed

• packages/markitdown/src/markitdown/converters/_image_converter.py
  • Imports llm_caption from ._llm_caption and calls it in convert() with the same arguments as before: stream, stream info, client, model, prompt=kwargs.get("llm_prompt").
  • Deletes _get_llm_description.
  • Removes the base64, mimetypes and Union imports, which only that method used.
• packages/markitdown/tests/test_image.py
  • test_image_without_llm_is_unchanged now patches image_module.llm_caption instead of ImageConverter._get_llm_description, so it still checks that no caption call happens when no LLM is configured.
  • Adds tests that pin the delegation and the behaviour it has to keep (listed below).
• packages/markitdown/tests/test_module_misc.py
  • Deletes the TODO in test_markitdown_llm_parameters. The image and PPTX assertions both stay: they exercise two different converters end to end, and each converter decides on its own whether to forward llm_prompt.

How it works

llm_caption is imported as a module-level name in _image_converter.py. That matches how _pptx_converter.py imports it, and tests (and anyone extending the converter) can patch it in one place per converter module: monkeypatch.setattr(image_module, "llm_caption", ...). Existing PPTX tests already do this.

The call site in convert() keeps everything around it the same:

• The caption is only requested when both llm_client and llm_model are set.
• A None return is skipped, and anything else is stripped and appended under # Description:.
• No try/except was added. Before this change, an exception from client.chat.completions.create propagated out of ImageConverter.convert(), and it still does. PptxConverter catches caption failures and falls back to its own handling. I left that difference alone because changing it would change behaviour.

Alternatives I considered:

• Keep _get_llm_description as a thin wrapper around llm_caption. That would keep a subclass override point, but it is a private method, nothing in the repo overrides it (I checked markitdown and markitdown-ocr), and keeping it would leave two names for one operation.
• Move the helper onto DocumentConverter or a mixin. That is a bigger API decision, and it belongs with the CLI and vision-caption unification work, not this cleanup.
• Merge the image and PPTX assertions in test_module_misc.py into one, as the TODO suggested. I did not do this. Sharing the helper does not prove that each converter passes llm_prompt through, and those two assertions are what check it.

Overlap with #1254

Open PR #1254 covers the same duplication, and the TODO removed here links to it. This PR is deliberately narrow: one call site moves to the existing helper, and nothing else changes behaviour. If #1254 lands first, this PR can be closed or rebased down to the extra tests. If this one lands first, #1254 will need a rebase where it touches _image_converter.py and the TODO. Reviewers on both may want to agree which one goes first.

Tests

packages/markitdown/tests/test_image.py

• test_image_without_llm_is_unchanged (updated): with no LLM configured, llm_caption is not called and the output is the metadata only.
• test_image_converter_uses_shared_llm_caption: image_module.llm_caption is the same object as _llm_caption.llm_caption and _pptx_converter.llm_caption, and ImageConverter no longer has _get_llm_description.
• test_image_converter_delegates_to_llm_caption (run with and without llm_prompt): convert() calls llm_caption once with the original stream, stream info, client, model and prompt, strips the returned caption, formats it under # Description:, and does not call the client directly.
• test_image_converter_skips_description_when_llm_caption_returns_none: a None caption leaves the metadata output as it is, with no description heading.
• test_image_converter_requires_client_and_model_for_caption (run with only a client, then only a model): llm_caption is not called unless both are set.
• test_image_converter_default_prompt_via_llm_caption (prompt None, "", " "): the request goes through the real helper and sends the default prompt.
• test_llm_caption_builds_data_uri_and_restores_stream: checks content-type resolution three ways (explicit mimetype wins over extension, extension-based guess, application/octet-stream fallback). It also checks that the data URI encodes only the bytes from the current position onward, that the stream position is restored afterwards, and that the custom prompt and model are passed through.

packages/markitdown/tests/test_module_misc.py

• test_markitdown_llm_parameters: only the TODO comment is removed. It still checks that llm_prompt reaches the client for both a JPEG and a PPTX.

To run them:

(cd 'packages/markitdown' && python3 -m unittest discover -s tests -p 'test_image.py') && (cd 'packages/markitdown' && python3 -m unittest discover -s tests -p 'test_module_misc.py')

The full suite and lint checks run through hatch test and pre-commit run --all-files.

Compatibility & risk

• Public API: no change. ImageConverter.convert() takes the same arguments and gives the same output for the same inputs.
• Removed private method: ImageConverter._get_llm_description no longer exists. Code that subclassed ImageConverter and overrode it, or patched it in tests, will no longer change captioning. That code should patch markitdown.converters._image_converter.llm_caption instead. Nothing in this repo or in markitdown-ocr relies on the old method.
• Error handling: unchanged. Exceptions from the client still propagate from ImageConverter, and the stream-read failure path still returns None and is skipped.
• Performance: none. The same single request is made.
• Where to look closely: the call site in convert() (_image_converter.py:71) and the overlap with Support Async LLM Client, reuse llm_caption helper #1254 described above.

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