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Sanjid Hasan
Sanjid Hasan

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What is Convolution?

Convolution – The Heart of Deep Learning ❤️

Convolution is a mathematical operation that combines two functions to produce a third function. In deep learning and computer vision, it is mainly used for feature extraction from images.


1️⃣ Understanding Convolution in Simple Terms

Imagine you have an image (a grid of pixel values) and a small filter (kernel) that slides over the image to detect patterns. This process is called convolution.

💡 Example:

  • A 3×3 filter slides over an image and performs a dot product with the pixels under it.
  • The result is a new, transformed image that highlights specific features (edges, textures, etc.).

2️⃣ How Does Convolution Work?

✔ Take a small filter (also called a kernel), e.g., a 3×3 matrix.

✔ Place it over a section of the image.

✔ Multiply the filter values with the corresponding pixel values.

✔ Sum them up → This gives one pixel in the output image.

✔ Slide the filter across the entire image and repeat.


3️⃣ Why is Convolution Important in AI?

Feature Extraction → Detects edges, textures, and patterns.

Reduces Complexity → Helps focus only on important information.

Translation Invariance → Works regardless of where an object appears in the image.

Basis of CNNs → Used in Convolutional Neural Networks (CNNs), which power computer vision tasks.


4️⃣ Visualization of a 3×3 Convolution

Input Image (5×5)

1  2  3  4  5  
6  7  8  9  10  
11 12 13 14 15  
16 17 18 19 20  
21 22 23 24 25  
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3×3 Filter (Edge Detector)

0  1  0  
1 -4  1  
0  1  0  
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Output (After Applying Convolution)

  0   1   0   1   0  
  1  -4   1  -4   1  
  0   1   0   1   0  
  1  -4   1  -4   1  
  0   1   0   1   0  
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👉 This detects edges in the image! 🚀


5️⃣ Types of Convolutions in Deep Learning

📌 Standard Convolution → Feature extraction.

📌 1D Convolution → Used in audio/signal processing.

📌 2D Convolution → Used in image processing (CNNs).

📌 3D Convolution → Used in video & volumetric data.

📌 Depthwise & Pointwise Convolution → Used in efficient CNNs like MobileNet.


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