Crop/trim a JPG file with empty space with Java

问题:

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?

回答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"));
    }
}

回答2:

For Android users, here is an example using Mike Kwan Answer:

    public static Bitmap TrimImage(Bitmap bmp) {
    int imgHeight = bmp.getHeight();
    int imgWidth  = bmp.getWidth();

    //TRIM WIDTH
    int widthStart  = imgWidth;
    int widthEnd = 0;
    for(int i = 0; i < imgHeight; i++) {
        for(int j = imgWidth - 1; j >= 0; j--) {
            if(bmp.getPixel(j, i) != Color.TRANSPARENT &&
                    j < widthStart) {
                widthStart = j;
            }
            if(bmp.getPixel(j, i) != Color.TRANSPARENT &&
                    j > widthEnd) {
                widthEnd = j;
                break;
            }
        }
    }
    //TRIM HEIGHT
    int heightStart = imgHeight;
    int heightEnd = 0;
    for(int i = 0; i < imgWidth; i++) {
        for(int j = imgHeight - 1; j >= 0; j--) {
            if(bmp.getPixel(i, j) != Color.TRANSPARENT &&
                    j < heightStart) {
                heightStart = j;
            }
            if(bmp.getPixel(i, j) != Color.TRANSPARENT &&
                    j > heightEnd) {
                heightEnd = j;
                break;
            }
        }
    }

    int finalWidth = widthEnd - widthStart;
    int finalHeight = heightEnd - heightStart;

    return Bitmap.createBitmap(bmp, widthStart,heightStart,finalWidth, finalHeight);
}

Hope this help someone :)

EDIT:

Guys, I just updated my answer cuz last code was just trimming the end of the image, not the beginning. This one is working just great :)