Detailed explanation of how to calculate PPI on screen using Java

introduction

In modern electronic devices, the resolution and display effect of the screen are an indicator that users are very concerned about. PPI (Pixels Per Inch, pixels per inch) is one of the important parameters to measure the accuracy of the screen display. The higher the PPI, the more delicate the image displayed on the screen, and the better the visual effect. This article will introduce the concepts and calculation methods of PPI in detail, and implement PPI calculations through Java code to help readers understand this technical indicator in depth.

What is PPI?

PPI (Pixels Per Inch) refers to the number of pixels per inch on the screen. It is one of the key indicators for measuring the accuracy of the screen display. The calculation formula of PPI is as follows:

[
\text{PPI} = \frac{\sqrt{\text{screen width}^2 + \text{screen height}^2}}{\text{screen diagonal length (inch)}}
]

in:

Screen widthandScreen heightIt is the resolution of the screen, in pixels.
Diagonal length of the screenIt is the physical size of the screen, in inches.

The higher the PPI value, the clearer the image displayed on the screen. For example, the iPhone's Retina screen PPI usually exceeds 300, while the PPI of a regular monitor may be around 100.

Why do I need to calculate PPI?

Evaluate the screen display effect
PPI is an important indicator for measuring the accuracy of screen display. By calculating the PPI, you can intuitively understand the display effect of the screen.
Equipment purchase reference
PPI is an important reference indicator when purchasing mobile phones, monitors and other devices. Devices with high PPI usually show better results.
Development adaptation
In mobile applications or web development, understanding the device's PPI helps optimize interface design and ensures that good display results can be achieved on different devices.

How to calculate PPI?

The calculation formula of PPI is based on the Pythagorean theorem. Assuming that the screen resolution is ( \text{width} \times \text{height} ) and the screen diagonal length is ( \text{diagonal} ) inches, the calculation steps of PPI are as follows:

Calculate the number of pixels in the diagonal of the screen:
[
\text{Diagonal pixel count} = \sqrt{\text{width}^2 + \text{height}^2}
]
Divide the number of diagonal pixels by the length of the screen diagonal (inches):
[
\text{PPI} = \frac{\text{number of diagonal pixels}}{\text{diagonal}}
]
Rounding (optional):
If integer results are required, the PPI can be rounded.

Java implements PPI computing

Below is a complete Java program for computing the PPI of the screen.

Code implementation

public class PPICalculator {

    /**
      * Calculate the PPI of the screen (pixels per inch)
      *
      * @param screenWidth Screen Width (pixels)
      * @param screenHeight Screen Height (pixels)
      * @param screenInch Diagonal length of screen (in inches)
      * @return PPI value (integer)
      */
    public static int calculatePPI(int screenWidth, int screenHeight, double screenInch) {
        // Calculate the number of diagonal pixels        double diagonalPixels = ((screenWidth, 2) + (screenHeight, 2));

        // Calculate PPI        double ppi = diagonalPixels / screenInch;

        // round and return        return (int) ppi;
    }

    public static void main(String[] args) {
        // Sample data: Screen width 720 pixels, height 1280 pixels, diagonal length 5.0 inches        int screenWidth = 720;
        int screenHeight = 1280;
        double screenInch = 5.0;

        // Calculate PPI        int ppi = calculatePPI(screenWidth, screenHeight, screenInch);

        // Output result        ("Screen Width (Pixel): " + screenWidth);
        ("Screen height (pixel): " + screenHeight);
        ("Screen Diagonal Length (Inches): " + screenInch);
        ("PPI: " + ppi);
    }
}

Code description

calculatePPI method
This method takes the screen width, height, and diagonal length as parameters, calculates and returns the PPI value. The calculation process is divided into the following steps:
- Use Pythagorean theorem to calculate the number of pixels in the diagonal of the screen.
- Divide the number of diagonal pixels by the length of the screen diagonal to get the PPI.
- Round the PPI and return it.
Main method
existmainIn the method, the resolution (720x1280 pixels) and diagonal length (5.0 inches) of an example screen are defined, and thecalculatePPIThe method calculates the PPI and outputs the result.

Sample output

Run the above code and the output result is as follows:

Screen width（Pixels）: 720
Screen height（Pixels）: 1280
Diagonal length of the screen（inch）: 5.0
PPI: 293

Code optimization and extension

1. Support floating point PPI

If you need to preserve the decimal part of the PPI, you can change the return type todouble, and remove the rounding operation:

public static double calculatePPI(int screenWidth, int screenHeight, double screenInch) {
    double diagonalPixels = ((screenWidth, 2) + (screenHeight, 2));
    return diagonalPixels / screenInch;
}

2. Support user input

Can be passedScannerClass implements user input screen parameters:

import ;

public class PPICalculator {

    public static void main(String[] args) {
        Scanner scanner = new Scanner();

        // Get user input        ("Please enter the screen width (pixel): ");
        int screenWidth = ();

        ("Please enter the screen height (pixel): ");
        int screenHeight = ();

        ("Please enter the diagonal length of the screen (in inches): ");
        double screenInch = ();

        // Calculate PPI        int ppi = calculatePPI(screenWidth, screenHeight, screenInch);

        // Output result        ("PPI: " + ppi);
    }
}

3. Support multi-device comparison

It can be extended to support computing the PPIs of multiple devices and comparing:

public static void comparePPI(int[] widths, int[] heights, double[] inches) {
    for (int i = 0; i &lt; ; i++) {
        int ppi = calculatePPI(widths[i], heights[i], inches[i]);
        ("equipment " + (i + 1) + " PPI: " + ppi);
    }
}

Practical application scenarios

Mobile phone screen selection
When purchasing a mobile phone, you can compare the display effects of different models by calculating PPI.
Monitor selection
For designers or programmers, high PPI displays can provide clearer image and text displays.
Application development adaptation
When developing mobile applications, understanding the device's PPI helps optimize UI design and ensures that good display results can be achieved on different devices.

Summarize

PPI is an important indicator for measuring the accuracy of screen display. Through simple mathematical formulas and Java code, we can easily calculate the PPI of the screen. This article introduces the concepts and calculation methods of PPI in detail, and provides a complete Java code implementation. I hope this article can help readers better understand PPI and play a role in practical applications.

The above is a detailed explanation of the method of using Java to calculate the PPI on the screen. For more information about the PPI on the Java to calculate the PPI on the screen, please pay attention to my other related articles!