Image Classification: Types, Methods and Examples
Image classification, also called odd one out, is a non-verbal reasoning topic in which four or five figures are given and all but one of them share a common property; the candidate must find the figure that does not share that property. The common figure is called the odd one out, and it is chosen by comparing the figures on visible properties such as shape, number of sides, symmetry and shading.
This topic is asked in APSC, ADRE, Assam Police, DHS, DME, SSC and Railway examinations because it tests careful comparison and the ability to find a simple common rule among pictures. It needs no calculation, and it can be solved quickly once the candidate learns which properties to compare. This article gives a complete deep-study revision of image classification: the basic terms, the core rules, the types of questions, the step-by-step method, the common mistakes and a practical preparation plan.
Basic Terms
- Classification: grouping things that share a common property and separating the one that does not.
- Odd one out: the single figure that does not share the common property of the others.
- Property: a feature of a figure, such as shape, number of sides or shading.
- Similarity: the property that all the figures except one share.
- Difference: the property that sets the odd figure apart.
- Symmetry: the property of a figure that can be divided into matching halves.
- Closed figure: a figure whose boundary does not have a free end.
- Open figure: a figure whose boundary has a free end.
- Equal parts: sections of a figure that are identical in size and shape.
- Orientation: the direction in which a figure is placed.
- Criterion: the property chosen to separate the odd figure.
- Majority property: the property held by most of the given figures.
- Distinctive feature: a small detail, such as a dot or a curve, that only one figure has.
Core Concepts and Rules
- Look for the property that is common to all the figures except one.
- Count the number of sides, corners or lines of each figure.
- Check whether the figures are open or closed.
- Check whether the figures are made of straight lines, curved lines, or both.
- Check the number of small elements such as dots, circles or arrows.
- Check the symmetry of each figure and the number of equal parts.
- Check the shading, such as filled, half-filled or empty parts.
- Check the orientation, because a figure that is rotated differently may be the odd one.
- The odd figure must fail the majority property; every other figure must have it.
- When two properties seem common, use the one that fails for exactly one figure.
Types of Image Classification Questions
The first type classifies figures by their shape, such as all triangles except one square. The second type classifies by the number of elements, such as all figures with three dots except one with four. The third type classifies by symmetry, such as all symmetrical figures except one that is not. The fourth type classifies by the number of sides or lines. The fifth type combines two properties, so the odd figure is the one that breaks both the shape rule and the count rule.
Steps to Solve an Image Classification Question
First, look at all the figures once and note the property that most of them seem to share. Second, test that property on every figure one by one. Third, count the sides, corners, lines and small elements to be sure. Fourth, check the shading, symmetry and open or closed nature. Fifth, find the single figure that fails the common property; that is the answer. Finally, confirm that every other figure really does share the property.
Examination Trends
In competitive examinations image classification usually carries two to four marks. Sets of five figures with one odd figure are the most common, and the property is usually the number of sides, the number of small elements or symmetry. Figures made of lines and dots appear often, and some questions use shaded parts. Because the topic needs no calculation and only careful comparison, a candidate who practises counting sides and elements can answer these questions in a short time.
Common Mistakes to Avoid
- Do not decide the odd figure by a quick look; test the property on every figure.
- Do not choose a figure because it looks different in colour or size alone.
- Do not forget to count the dots, lines and corners exactly.
- Do not ignore whether the figures are open or closed.
- Do not confuse a rotated figure with a truly different figure.
- Do not stop at the first difference; check that all the others share the property.
How to Prepare This Topic
Begin by grouping simple figures by shape and then by the number of sides, and say what the common property is. Then practise sets in which the odd figure is found by counting dots or corners. After that, work with shaded and symmetrical figures and time yourself. Keep a note of the properties you keep forgetting and revise them in short sessions.
A useful method is to write one property at a time at the top of the page and tick the figures that have it, so that the unticked figure stands out. Another method is to compare the figures two at a time to see which property they share. Daily practice of twenty to twenty-five questions for a few days makes comparison automatic, and the same skill helps in embedded figure and figure analogy questions as well.
Quick Revision Tips
- Tick the figures that have the chosen property; the unticked one is the answer.
- Count sides, corners, dots and lines exactly before deciding.
- Check open and closed figures as well.
- Do not treat a rotated figure as a different figure.
- Compare the figures two at a time to find the common property.
- Confirm that every other figure really shares the property before answering.
Final Revision Note
In the final revision, sort a mixed set of figures by shape, then by number of sides, then by dots, and note which type of property is used most often. Practise sets where the difference lies in symmetry or shading as well, because these are the traps that slow candidates down. With steady practice the comparison becomes automatic and the odd figure stands out at a glance.
Frequently Asked Questions
What is image classification in reasoning?
It is a non-verbal reasoning topic in which all but one of the given figures share a common property and the candidate must find the odd figure.
What properties should I compare?
Compare shape, number of sides and corners, number of small elements, symmetry, open or closed boundary, shading and orientation.
How many figures are usually given?
Four or five figures are given, and all but one share a common property.
Can a rotated figure be the odd one?
Usually a rotated figure is still the same figure, so it is not the odd one unless the question is based on orientation; check the property carefully.
Which exams ask image classification questions?
APSC, ADRE, Assam Police, DHS, DME, SSC and Railway examinations ask image classification questions in the non-verbal reasoning section.