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I'm working on creating a model that locates the object in the scene (2D image or 3D scene) using a natural language query. I came across this paper on natural language object retrieval which mentions that this task is different from text-based image retrieval in the sense that natural language object retrieval requires an understanding of objects in the image, spatial configurations, etc. I am not able to see the difference between these two tasks. Could you please explain it with an example?

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Disclaimer: I can only answer for the NLP part since I'm no expert for image processing.

I assume that text-based image retrieval is the task of finding the image (or the part of an image) which corresponds to a short text which exclusively describes the object. Practically it means that any content word (i.e. excluding grammatical words like determiners) in the text refers directly to the object: "a bike", "a black cat", "the red car", etc. For a ML process it means that there's nothing to analyze in the text, every word can directly be associated with a characteristic of the image.

By contrast Natural Language object retrieval involves analyzing the text. For instance "the cat on the left of the picture" is different than "the picture on the left of the cat", even though the words are the same. Additionally there can be different ways to refer to the same object: "the book at the left of the shelf" may be the same as "the leftmost book" or "the book next to the green book". There are usually many ways to express the same meaning with language, and that makes the task much more complex. Additionally I would assume that mapping positional descriptions to the image characteristics can be tricky: "the man behind the tree" or "the second bridge" in a 2D image requires the model to "understand" depth. In a picture with two dogs, "the small dog" requires the model to "understand" size relation between objects. Humans intuitively know how to interpret these sentences, but for a machine Natural Language Understanding hasn't been solved yet (it might never be).

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  • $\begingroup$ Thanks for your response. If we have natural language descriptions where each description is annotated with an object label (or object id) from the 2D images or 3D scenes, and we also have bounding boxes of objects in the scenes, if we train a model using this annotated dataset, will the model be able to learn things like "spatial relations" between main object and other reference objects? What's the best way to train natural language descriptions and 2D/3D images? Is it by jointly embedding images and descriptions? Any advice to train such a model would be of great help! $\endgroup$ – Sid Oct 11 '20 at 1:44
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    $\begingroup$ @Sid I don't know, apparently the paper you mentioned shows that it's possible so I guess you should try their method. In general joint learning often gives better results but requires much more instances. But I guess it mostly depends how diverse is the language: if most of the descriptions just use standard expressions like "left of, right of, above, below", it's much easier than if there are many different ways to express the same thing like in my examples. $\endgroup$ – Erwan Oct 11 '20 at 9:34

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