How to scale a BufferedImage

Question

Following the javadocs  I have tried to scale a BufferedImage without success here is my code   BufferedImage image   MatrixToImageWriter getBufferedImage encoded   Graphics2D grph   image createGraphics    grph scale 2 0  2 0   grph dispose      I can t understand why it is not working  any help

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scale     works a bit differently  You can use bufferedImage getScaledInstance

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As  Bozho says  you probably want to use getScaledInstance   To understand how grph scale 2 0  2 0  works however  you could have a look at this code   import java awt    import java awt image BufferedImage  import java io     import javax imageio ImageIO  import javax swing ImageIcon    class Main       public static void main String   args  throws IOException            final int SCALE   2           Image img   new ImageIcon  duke png   getImage             BufferedImage bi   new BufferedImage SCALE   img getWidth null                                                SCALE   img getHeight null                                                BufferedImage TYPE INT ARGB            Graphics2D grph    Graphics2D  bi getGraphics            grph scale SCALE  SCALE               everything drawn with grph from now on will get scaled           grph drawImage img  0  0  null           grph dispose             ImageIO write bi   png   new File  duke double size png               Given duke png   it produces duke double size png

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Using imgscalr     Java Image Scaling Library   BufferedImage image        Scalr resize originalImage  Scalr Method BALANCED  newWidth  newHeight     This is fast enough for me

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To scale an image  you need to create a new image and draw into it  One way is to use the filter   method of an AffineTransferOp  as suggested here  This allows you to choose the interpolation technique    private static BufferedImage scale1 BufferedImage before  double scale        int w   before getWidth        int h   before getHeight           Create a new image of the proper size     int w2    int   w   scale       int h2    int   h   scale       BufferedImage after   new BufferedImage w2  h2  BufferedImage TYPE INT ARGB       AffineTransform scaleInstance   AffineTransform getScaleInstance scale  scale       AffineTransformOp scaleOp            new AffineTransformOp scaleInstance  AffineTransformOp TYPE BILINEAR        scaleOp filter before  after       return after      Another way is to simply draw the original image into the new image  using a scaling operation to do the scaling  This method is very similar  but it also illustrates how you can draw anything you want in the final image   I put in a blank line where the two methods start to differ    private static BufferedImage scale2 BufferedImage before  double scale        int w   before getWidth        int h   before getHeight           Create a new image of the proper size     int w2    int   w   scale       int h2    int   h   scale       BufferedImage after   new BufferedImage w2  h2  BufferedImage TYPE INT ARGB       AffineTransform scaleInstance   AffineTransform getScaleInstance scale  scale       AffineTransformOp scaleOp            new AffineTransformOp scaleInstance  AffineTransformOp TYPE BILINEAR        Graphics2D g2    Graphics2D  after getGraphics           Here  you may draw anything you want into the new image  but we re        drawing a scaled version of the original image      g2 drawImage before  scaleOp  0  0       g2 dispose        return after      Addendum  Results    To illustrate the differences  I compared the results of the five methods below  Here is what the results look like  scaled both up and down  along with performance data   Performance varies from one run to the next  so take these numbers only as rough guidelines   The top image is the original  I scale it double-size and half-size    As you can see  AffineTransformOp filter    used in scaleBilinear    is faster than the standard drawing method of Graphics2D drawImage   in scale2    Also BiCubic interpolation is the slowest  but gives the best results when expanding the image   For performance  it should only be compared with scaleBilinear   and scaleNearest     Bilinear seems to be better for shrinking the image  although it s a tough call  And NearestNeighbor is the fastest  with the worst results  Bilinear seems to be the best compromise between speed and quality  The Image getScaledInstance    called in the questionable   method  performed very poorly  and returned the same low quality as NearestNeighbor   Performance numbers are only given for expanding the image      public static BufferedImage scaleBilinear BufferedImage before  double scale        final int interpolation   AffineTransformOp TYPE BILINEAR      return scale before  scale  interpolation      public static BufferedImage scaleBicubic BufferedImage before  double scale        final int interpolation   AffineTransformOp TYPE BICUBIC      return scale before  scale  interpolation      public static BufferedImage scaleNearest BufferedImage before  double scale        final int interpolation   AffineTransformOp TYPE NEAREST NEIGHBOR      return scale before  scale  interpolation       NotNull private static  BufferedImage scale final BufferedImage before  final double scale  final int type        int w   before getWidth        int h   before getHeight        int w2    int   w   scale       int h2    int   h   scale       BufferedImage after   new BufferedImage w2  h2  before getType         AffineTransform scaleInstance   AffineTransform getScaleInstance scale  scale       AffineTransformOp scaleOp   new AffineTransformOp scaleInstance  type       scaleOp filter before  after       return after            This is a more generic solution  It produces the same result  but it shows how you     can draw anything you want into the newly created image  It s slower     than scaleBilinear        param before The original image     param scale The scale factor     return A scaled version of the original image     private static BufferedImage scale2 BufferedImage before  double scale        int w   before getWidth        int h   before getHeight           Create a new image of the proper size     int w2    int   w   scale       int h2    int   h   scale       BufferedImage after   new BufferedImage w2  h2  before getType         AffineTransform scaleInstance   AffineTransform getScaleInstance scale  scale       AffineTransformOp scaleOp               new AffineTransformOp scaleInstance  AffineTransformOp TYPE BILINEAR        Graphics2D g2    Graphics2D  after getGraphics           Here  you may draw anything you want into the new image  but we re just drawing        a scaled version of the original image  This is slower than         calling scaleOp filter        g2 drawImage before  scaleOp  0  0       g2 dispose        return after            I call this one  questionable  because it uses the questionable getScaledImage       method  This method is no longer favored because it s slow  as my tests confirm      param before The original image     param scale The scale factor     return The scaled image      private static Image questionable final BufferedImage before  double scale        int w2    int   before getWidth     scale       int h2    int   before getHeight     scale       return before getScaledInstance w2  h2  Image SCALE FAST

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Unfortunately the performance of getScaledInstance   is very poor if not problematic   The alternative approach is to create a new BufferedImage and and draw a scaled version of the original on the new one   BufferedImage resized   new BufferedImage newWidth  newHeight  original getType     Graphics2D g   resized createGraphics    g setRenderingHint RenderingHints KEY INTERPOLATION      RenderingHints VALUE INTERPOLATION BILINEAR   g drawImage original  0  0  newWidth  newHeight  0  0  original getWidth        original getHeight    null   g dispose      newWidth newHeight indicate the new BufferedImage size and have to be properly calculated  In case of factor scaling   int newWidth   new Double original getWidth     widthFactor  intValue    int newHeight   new Double original getHeight     heightFactor  intValue      EDIT  Found the article illustrating the performance issue  The Perils of Image getScaledInstance

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If you do not mind using an external library  Thumbnailator can perform scaling of BufferedImages   Thumbnailator will take care of handling the Java 2D processing  such as using Graphics2D and setting appropriate rendering hints  so that a simple fluent API call can be used to resize images   BufferedImage image   Thumbnails of originalImage  scale 2 0  asBufferedImage      Although Thumbnailator  as its name implies  is geared toward shrinking images  it will do a decent job enlarging images as well  using bilinear interpolation in its default resizer implementation     Disclaimer  I am the maintainer of the Thumbnailator library

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AffineTransformOp offers the additional flexibility of choosing the interpolation type   BufferedImage before   getBufferedImage encoded   int w   before getWidth    int h   before getHeight    BufferedImage after   new BufferedImage w  h  BufferedImage TYPE INT ARGB   AffineTransform at   new AffineTransform    at scale 2 0  2 0   AffineTransformOp scaleOp       new AffineTransformOp at  AffineTransformOp TYPE BILINEAR   after   scaleOp filter before  after     The fragment shown illustrates resampling  not cropping  this related answer addresses the issue  some related examples are examined here

[java] How to scale a BufferedImage

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