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{{Short description|Detecting small objects in digital images}}
'''Small object detection''' is a particular case of [[object detection]] where various techniques are employed to detect small objects in digital images and videos. "Small objects" are objects having a small pixel footprint in the input image. In areas such as [[Aerial photography|aerial imagery]], [[State of the art|state-of-the-art]] object detection techniques
== Uses ==
[[File:Track_Results.webm|thumb|An example of object tracking]]
Small object detection has applications in various fields such as Video [[surveillance]] (Traffic video Surveillance,<ref>{{Cite
== Problems with small objects ==
* Modern-day object detection algorithms such as [[You Only Look Once
* Sometimes, the shadow of an object is detected as a part of object itself.<ref>{{Cite
* At present, [[Unmanned aerial vehicle|drones]] are very widely used in aerial imagery.<ref>{{Cite
[[File:Disp_shadow.jpg|thumb|Shadow and drone movement effect|alt=Here, both images are from same video. See, How the shadow of objects affecting detection accuracy. Also, drone's self-movement changes the scene near boundary(Refer to object "car" at bottom-left corner).]]
== Methods ==
Various methods<ref>{{Cite
[[File:Yolov5 (Ariel top view of Ahmedabad, Gujarat, India, 2022).jpg|thumb|YOLOv5 detection result]]
[[File:
[[File:Yolov7 (Ariel top view of Ahmedabad, Gujarat, India, 2022).jpg|thumb|YOLOv7 detection output
=== Improvising existing techniques ===
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==== Choosing a data set that has small objects ====
The [[machine learning]] model's output depends on "How well it is trained."<ref name=":0">{{Cite journal |
==== Generating more data via augmentation, if required ====
[[Deep learning]] models have billions of neurons that settle down to some weights after training. Therefore, it requires a good amount of quantitative and qualitative data for better training.<ref>{{Cite web |title=The Size and Quality of a Data Set {{!}} Machine Learning |url=https://developers.google.com/machine-learning/data-prep/construct/collect/data-size-quality |access-date=2022-09-14 |website=Google Developers |language=en}}</ref> [[Data augmentation]] is useful technique to generate more diverse data<ref name=":0" /> from an existing data set.
==== Increasing image capture resolution and model’s input resolution ====
These help to get more features from objects and eventually learn the best from them. For example, a bike object in the 1280 X 1280 [[Image resolution|resolution]] image has more features than the 640 X 640 resolution.
==== Auto learning anchors ====
Selecting anchor size plays a vital role in small object detection.<ref>{{
==== Tiling approach during training and inference ====
State-of-the-art object detectors allow only the fixed size of image and change the input image size according to it. This change may deform the small objects in the image. The tiling approach<ref>{{Cite
==== Feature Pyramid Network (FPN) ====
Use a feature [[Pyramid (image processing)|pyramid]] network<ref>{{
=== Add-on techniques ===
Instead of modifying existing methods, some add-on techniques are there, which can be directly placed on top of existing approaches to detect smaller objects. One such technique is Slicing Aided Hyper Inference(SAHI).<ref>{{
=== Well-Optimised techniques for small object detection ===
Various deep learning techniques are available that focus on such object detection problems: e.g., Feature-Fused SSD,<ref>{{Cite
== Other applications ==
* Crowd counting<ref>{{Cite
* Vehicle re-identification<ref>{{Cite journal |
* Animal detection<ref>{{Cite
* Fish detection<ref>{{Cite
== See also ==
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== External links ==
* [https://github.com/VisDrone/VisDrone-Dataset VisDrone] dataset by AISKYEYE team at Lab of Machine Learning and Data Mining, Tianjin University, China.
{{Computer vision}}
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