How To Determine Pixel Per Meter In Matlab

How To Articles

When using digital images and computer vision in MATLAB, it is vital to comprehend the idea of pixel per meter (PXM). PXM signifies the quantity of pixels encompassed within a meter in an image. This measure is critical for precisely comprehending distances and dimensions in an image. In this article, I will lead you through the steps of determining the PXM value in MATLAB, offering elaborate explanations and my own perspectives throughout the process.

First, let’s start by understanding the relationship between pixels and physical measurements. In an image, pixels are the smallest units of information that make up the image. Each pixel has a specific color or grayscale value, and together, they form the complete image. However, without considering the physical dimensions, a pixel is just a digital representation of data.

To determine the pixel per meter value in MATLAB, we need to establish a reference object within the image with known physical dimensions. This reference object can be anything with known length or size, such as a ruler or an object of known dimensions. By measuring the number of pixels occupied by the reference object, we can calculate the PXM value.

Next, let’s dive into the implementation details in MATLAB. Here’s a step-by-step guide:

Step 1: Read and Display the Image

image = imread('image.jpg');

Replace ‘image.jpg’ with the path to your image file. This code reads and displays the image on the MATLAB figure window, allowing you to visualize the image before proceeding.

Step 2: Select and Measure the Reference Object


Use the MATLAB figure window to select the reference object by clicking and dragging a rectangle around it. Once selected, measure the length or size of the reference object using an external tool, such as a ruler. Note down the measured value in meters.

Step 3: Calculate the Pixel per Meter Value

reference_length = ; % measured length of the reference object in meters
reference_pixels = ; % number of pixels occupied by the reference object
pxm_value = reference_pixels / reference_length;

In the above code, replace the reference_length with the measured length of the reference object in meters. Replace the reference_pixels with the number of pixels occupied by the reference object. This calculation divides the number of pixels by the length in meters, giving us the pixel per meter value.

By following these steps, you can determine the PXM value in MATLAB for any image. This value can be used to convert distances and sizes measured in pixels to their corresponding physical measurements.


Determining the pixel per meter value in MATLAB is a fundamental step in accurately interpreting distances and sizes within digital images. By selecting a reference object with known physical dimensions and measuring the number of pixels it occupies, we can calculate the PXM value. This value allows us to convert pixel measurements to their real-world counterparts. With this knowledge, you can confidently analyze and process images in MATLAB, unlocking a wide range of applications in computer vision and image processing.