How to Correctly Overlay Text onto a BufferedImage using Graphics2D?-javaTutorial-php.cn

How to Correctly Overlay Text onto a BufferedImage using Graphics2D?

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Release： 2024-12-21 12:49:09

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How to Correctly Overlay Text onto a BufferedImage using Graphics2D?

Using Graphics2D to Add Text Overlays on a BufferedImage

This question pertains to the overlaying of text onto a BufferedImage using Graphics2D. The aim is to render the final image with the added text.

Problem Description

The provided code snippet attempts to overlay text at specific coordinates using Graphics2D:

protected BufferedImage Process2(BufferedImage image){
    Graphics2D gO = image.createGraphics();
    gO.setColor(Color.red);
    gO.setFont(new Font( "SansSerif", Font.BOLD, 12 ));
    gO.drawString(this.text, this.x, this.y);
    System.err.println(this.text+this.x+this.y);
    return image;
}

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However, the output image remains unaltered.

Solution

1. Baseline for Text Rendering:

The drawString() method in Graphics2D interprets the specified coordinates as the baseline for the leftmost character. This implies that the text may be rendered outside the image if it contains characters that extend below the baseline, such as descenders in lower-case letters or numbers.

2. Image Color Model Compatibility:

The image's color model must be compatible with overlaying text. The provided code attempts to modify an image directly, which can cause unexpected results if the image has an incompatible color model.

Revised Code Using Rendered Text on Image:

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

public class TextOverlay {

    public static BufferedImage process(BufferedImage image, String text, int x, int y) {
        int w = image.getWidth();
        int h = image.getHeight();
        BufferedImage processed = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);

        // Create Graphics2D object for the processed image
        Graphics2D g2 = processed.createGraphics();

        // Transfer the contents of the original image to the processed image
        g2.drawImage(image, 0, 0, w, h, null);

        // Set the text color and font
        g2.setColor(Color.red);
        Font font = new Font("SansSerif", Font.BOLD, 12);
        g2.setFont(font);

        // Get the font metrics to determine the bounding box for the text
        FontMetrics fm = g2.getFontMetrics(font);
        int textWidth = fm.stringWidth(text);
        int textHeight = fm.getAscent() - fm.getDescent();

        // Calculate the coordinates for the text so that it is centered at the specified location
        int textX = x - textWidth / 2;
        int textY = y + textHeight / 2;

        // Draw the text on the processed image
        g2.drawString(text, textX, textY);

        // Dispose of the Graphics2D object
        g2.dispose();

        return processed;
    }
}

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Usage:

BufferedImage image = ... // Load your original image

String text = "Hello, world!";
int x = 100;
int y = 100;

BufferedImage processedImage = TextOverlay.process(image, text, x, y);

// Use the processed image as needed

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