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What does exactly and precisely the term "fine-grained" mean in image segmentation? For example, undeniably, the picture below is a fine-grained image:

enter image description here

But is it correct to call below picture as a fine-grained image?

enter image description here

or

enter image description here

I think it means a picture with details. In my idea, by accepting this definition, every picture out there can be called "fine-grained". Could anybody explain as precisely as possible what exactly a "fine-grained" image is?

Thanks in advance.

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  • $\begingroup$ If you have encountered an example of the kind of use of "fine grained" that the question is about, could you please quote the source verbatim? All I get by googling is about fine-grained image classification, which means: fine-grained classification of images. $\endgroup$ – Olli Niemitalo Oct 24 '15 at 21:26
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Just looking at the Google results I find:

This challenge will target fine-grained classification, i.e. classification among categories which are are both visually and semantically very similar. This is a very difficult regime which is even challenging for humans without careful training, and is critical for establishing a more detailed understanding of the visual world.

First, being a fine-grained categorization problem, there is little inter-class variation. For example the basset hound and bloodhound share very similar facial characteristics but differ significantly in their color, while the Japanese spaniel and papillion share very similar color but greatly differ in their facial characteristics.

So the upshot is that "fine-grained" means that the classes that are trying to be distinguished between are visually very similar.

In terms of a single image, it means that it is hard to see the differences across the entire image. In that case, your top image is fine-grained. The dog and bird images are not. Though if you zoomed into the hair of the dog or the feathers of the bird, I expect they would be.

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  • $\begingroup$ Now I am completely confused because literately, "fine-grained" means an image with high detailed image like the first one in the question. what about the image of a dog? is it a fine-grained? or even the bird? all of them can be called "fine-grained". in term of "classification", the definition you provided is OK but what about a single image? $\endgroup$ – David Oct 23 '15 at 16:27
  • $\begingroup$ @David : Updated answer for single image. $\endgroup$ – Peter K. Oct 23 '15 at 16:29
  • $\begingroup$ Thanks for your quick reply. But, what are differences between "fine-grained" images and "rich-texture" images? $\endgroup$ – David Oct 23 '15 at 16:47
  • $\begingroup$ That's not a term I've had much to do with, but it appears to mean "images with more happening in it than I really want". For example, a building that we want to extract the outline of has ivy growing on the outside to give it more unpredictable texture (and lots more edges) than I want. $\endgroup$ – Peter K. Oct 23 '15 at 17:06

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