What is convolution?

Gabriel Rennó
LatinXinAI
Published in
3 min readDec 7, 2022

Understand the fundamental technique for image processing.

Convolution is a mathematical operation that is commonly used in image processing. It is used to apply a filter or kernel to an image, resulting in a filtered version of the original image. This operation is called convolution because it involves the “sliding” of the filter over the image, multiplying the values of the filter and the image at each location, and summing the results to create a new value for the output image.

A convolution is a powerful tool for image processing because it allows us to extract information from images in a highly efficient manner. For example, we can use convolution to detect edges in an image, sharpen blurry images, or smooth out noisy images. In general, convolution is used to apply a wide range of transformations to images, including blurring, sharpening, edge detection, and many others.

One of the key features of convolution is that it is a linear operation. This means that the output of a convolution is simply the sum of the convolutions of the input with each individual component of the filter. This property makes convolution extremely efficient because we can compute the output of a convolution very quickly by simply multiplying each component of the filter with the corresponding component of the image and summing the results.

Another key feature of convolution is that it is shift-invariant. This means that the output of a convolution is the same, regardless of where the filter is applied within the image. This property is extremely useful for image processing because it means that we can apply the same filter to different parts of an image, and we will get the same result every time.

In order to perform convolution on an image, we first need to create a filter or kernel. A filter is simply a small matrix of numbers that defines the transformation that we want to apply to the image. For example, a filter might be used to detect edges in an image, in which case the filter would be designed to highlight differences in pixel intensity across the image.

Once we have defined our filter, we can apply it to the image by “sliding” it over the image, one pixel at a time. At each location, we multiply the values of the filter and the image at that location, and sum the results to create a new value for the output image. This process is repeated for every location in the image, resulting in a filtered version of the original image.

Convolution is a widely used technique in image processing, and it is an essential tool for many applications. It allows us to extract information from images in a highly efficient manner, and it can be used to apply a wide range of transformations to images. Whether you are a computer vision expert, a machine learning practitioner, or just someone who is interested in image processing, understanding convolution is an important step toward mastering this fascinating field.

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Gabriel Rennó
LatinXinAI

Masters student in Artificial Intelligence at Barcelona Technology School.