image - Crop/trim a JPG file with empty space with Java

Question

Is there a framework which is able to remove the white space (rectangular) of an image. We create Image Thumbnails from technical drawings which are unfortunately in PDF format. We convert the PDF to SVG and then to JPG. Often the technical drawings are very small and now placed in the upper left corner of the thumbnail:

+---------+----------------------+
|         |                      |
| (image) |                      |
|         |                      |
+---------+                      |
|                                |
|                                |
|                                |
|                                |
|              (empty space)     |
|                                |
|                                |
+--------------------------------+

So how can I easily remove the empty space and shrink the JPG file?

Answer 1

It can be done in JAI as is demonstrated in this thread. Or here's some Java code I just wrote which can be used to do it:

public class TrimWhite {
    private BufferedImage img;

    public TrimWhite(File input) {
        try {
            img = ImageIO.read(input);
        } catch (IOException e) {
            throw new RuntimeException( "Problem reading image", e );
        }
    }

    public void trim() {
        int width  = getTrimmedWidth();
        int height = getTrimmedHeight();

        BufferedImage newImg = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_RGB);
        Graphics g = newImg.createGraphics();
        g.drawImage( img, 0, 0, null );
        img = newImg;
    }

    public void write(File f) {
        try {
            ImageIO.write(img, "bmp", f);
        } catch (IOException e) {
            throw new RuntimeException( "Problem writing image", e );
        }
    }

    private int getTrimmedWidth() {
        int height       = this.img.getHeight();
        int width        = this.img.getWidth();
        int trimmedWidth = 0;

        for(int i = 0; i < height; i++) {
            for(int j = width - 1; j >= 0; j--) {
                if(img.getRGB(j, i) != Color.WHITE.getRGB() &&
                        j > trimmedWidth) {
                    trimmedWidth = j;
                    break;
                }
            }
        }

        return trimmedWidth;
    }

    private int getTrimmedHeight() {
        int width         = this.img.getWidth();
        int height        = this.img.getHeight();
        int trimmedHeight = 0;

        for(int i = 0; i < width; i++) {
            for(int j = height - 1; j >= 0; j--) {
                if(img.getRGB(i, j) != Color.WHITE.getRGB() &&
                        j > trimmedHeight) {
                    trimmedHeight = j;
                    break;
                }
            }
        }

        return trimmedHeight;
    }

    public static void main(String[] args) {
        TrimWhite trim = new TrimWhite(new File("...\someInput.bmp"));
        trim.trim();
        trim.write(new File("...\someOutput.bmp"));
    }
}