How to Maintain High Image Quality After Downscaling in Java?

How to Improve Image Quality After Resizing in Java

Downscaling an image significantly can often result in a noticeable drop in quality. However, by adopting a divide and conquer approach, you can mitigate this issue, ensuring your resized images maintain a higher level of detail.

Divide and Conquer Method:

Instead of scaling the image directly to its final size, break down the process into smaller steps. For example, to resize a 650x748 image to fit within 60x60, start by scaling it down to 325x374 (50% of the original size). Then, scale it down again to 162x187 (50% of the previous size). Finally, scale it to its target size of 60x60, resulting in a much higher quality image than if the resizing was done in one large step.

Example Code:

public static BufferedImage getScaledInstanceToFit(BufferedImage img, Dimension size) {
    float scaleFactor = getScaleFactorToFit(img, size);
    return getScaledInstance(img, scaleFactor);
}

public static float getScaleFactorToFit(BufferedImage img, Dimension size) {
    float scale = 1f;
    if (img != null) {
        int imageWidth = img.getWidth();
        int imageHeight = img.getHeight();
        scale = getScaleFactorToFit(new Dimension(imageWidth, imageHeight), size);
    }
    return scale;
}

public static float getScaleFactorToFit(Dimension original, Dimension toFit) {
    float scale = 1f;
    if (original != null && toFit != null) {
        float dScaleWidth = getScaleFactor(original.width, toFit.width);
        float dScaleHeight = getScaleFactor(original.height, toFit.height);
        scale = Math.min(dScaleHeight, dScaleWidth);
    }
    return scale;
}

Additional Tips:

• Use anti-aliasing: Anti-aliasing helps reduce jagged edges by blending adjacent pixels.
• High-quality rendering hints: Set the rendering hints to enable high-quality resizing and interpolation.
• Choose an appropriate interpolation algorithm: Use a high-quality interpolation algorithm such as bicubic or Lanczos for optimal results.
• Downscale moderately: Avoid excessive downscaling to preserve detail. Step down the image in smaller increments.

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