How to zoom an image using pixel replication

Zooming is one of the essential concepts of image processing. It simply means to enlarge an image so that its details become sharper and more visible. There are many applications of zooming that range from doing it through some lens to a digital image on some system.

There are three most widely zooming methods in image processing:

• Pixel replication or nearest neighbor interpolation

• Zero-order hold method

• K-times zooming

Each of the methods has its pros and cons. In this answer, we learn about zooming in on an image using pixel replication.

Pixel replication

Pixel replication is also known as nearest neighbor interpolation because using it we can only replicate the neighboring pixels. Let's see how this method work.

Methodology

In the pixel replication method, new pixels are produced through the existing pixels or already given pixels of the input image. Every pixel of the input picture is replicated $n$ times row-wise and $n$ times column-wise, and the input image gets zoomed.

Note: We apply this method first row wise, and then column wise.

Example

Let's try to understand this method using a 2 by 2 matrix, through an image having dimensions of two rows and two columns. Let's suppose we have the following matrix, and we zoom it twice using the pixel replication method:

To apply pixel replication, we follow two steps:

1. Row-wise zooming

2. Column-wise zooming

Row-wise zooming

With row-wise zooming, each pixel is replicated twice in the rows. This is a very simple process. We copy the pixels of the rows to their adjacent new cell. The new image is as follows:

Column-wise zooming

With column-wise zooming, we replicate each pixel column-wise as we did with the rows. We copy the column pixels to their adjacent new column. The new image is as follows:

Result

The dimensions produced by the pixel replication are 4*4, and the input image had dimensions of 2*2.

The formula for the new image dimensions is as follows:

Advantage

The pixel replication method of zooming has the following advantage:

• This method is easy to implement as the pixels are copied into adjacent rows and columns.

Disadvantage

The pixel replication method of zooming has the following disadvantage:

• The image produced by this method is always too blurry because of the increased zooming factor. As the zooming factor increases, the image gets more blurred.