How Can I Improve Image Quality After Downsizing in Java?

Improving Image Quality after Downsizing in Java

As you've noticed, resizing an image to a significantly smaller size can result in a noticeable loss of image quality. To remedy this issue, consider implementing the following:

Divide and Conquer Approach:

Instead of scaling the image down in one go, break it down into incremental steps. This reduces the overall scale factor, resulting in better quality.

Enhanced Rendering:

In your resizeImage() method, ensure you're setting suitable rendering hints to improve the interpolation algorithm and image quality. Consider using constants like:

RenderingHints.VALUE_INTERPOLATION_BILINEAR
RenderingHints.VALUE_RENDER_QUALITY
RenderingHints.VALUE_ANTIALIAS_ON

Resampling:

Experiment with different resampling algorithms, such as bicubic or Lanczos, which are known to produce higher quality results when scaling images up or down.

Sample Code:

Here's a revised version of your code that incorporates the suggested improvements:

public static Boolean resizeImage(String sourceImg, String destImg, Integer Width, Integer Height, Integer whiteSpaceAmount) {
    BufferedImage origImage;

    try {
        origImage = ImageIO.read(new File(sourceImg));
        int type = origImage.getType() == 0? BufferedImage.TYPE_INT_ARGB : origImage.getType();
        int fHeight = Height;
        int fWidth = Width;
        int whiteSpace = Height + whiteSpaceAmount; 

        double aspectRatio;

        // Determine resized dimensions
        if (origImage.getHeight() > origImage.getWidth()) {
            fHeight = Height;
            aspectRatio = (double)origImage.getWidth() / (double)origImage.getHeight();
            fWidth = (int)Math.round(Width * aspectRatio);
        } else {
            fWidth = Width;
            aspectRatio = (double)origImage.getHeight() / (double)origImage.getWidth();
            fHeight = (int)Math.round(Height * aspectRatio);
        }

        BufferedImage scaledImage = new BufferedImage(whiteSpace, whiteSpace, type);
        Graphics2D g = scaledImage.createGraphics();
        g.setColor(Color.white);
        g.fillRect(0, 0, whiteSpace, whiteSpace);

        g.setComposite(AlphaComposite.Src);
        g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
        g.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        // Instead of scaling directly to fHeight/fWidth, do it in steps 
        int step = 2; 
        while (fHeight > 0 && fWidth > 0) {
            g.drawImage(origImage, (whiteSpace - fWidth)/2, (whiteSpace - fHeight)/2, fWidth, fHeight, null);
            origImage = scaledImage;
            fWidth /= step;
            fHeight /= step;
        }

        g.dispose();

        ImageIO.write(scaledImage, "jpg", new File(destImg));
    } catch (IOException ex) {
        return false;
    }

    return true;
}

By implementing these enhancements, you should see improved image quality when downsizing images, particularly for larger scale factors.

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