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I have a single .png image with several icons on it (with transparent areas) and would like to crop individual icons from it. In Java ME it was rather straight-forward, but in BlackBerry I haven't found an equivalent. The code here shows an example with a Bitmap, however doing so paints the transparent areas with white color:

public Bitmap cropImage(Bitmap image, int x, int y, int width, int height) {
    Bitmap result = new Bitmap(width, height);
    Graphics g = new Graphics(result);
    g.drawBitmap(0, 0, width, height, image, x, y);
    return result;
}

I need the same for an EncodedImage to keep the transparency, but Graphics constructor accepts only a Bitmap. Is there any other way to accomplish this? Thank you for any tips.

UPDATE:

Transparency can be preserved if you omit the intermediate Graphics object altogether, and set the ARGB data directly to the newly created Bitmap, like so:

public Bitmap cropImage(Bitmap image, int x, int y, int width, int height) {
    Bitmap result = new Bitmap(width, height);
    int[] argbData = new int[width * height];
    image.getARGB(argbData, 0, width, x, y, width, height);
    result.setARGB(argbData, 0, width, 0, 0, width, height);
    return result;
}
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Levon
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  • Apparently there's no way to return a cropped image (from a larger image), while also keeping the transparency. I worked around this by passing the graphics context into my method, and drawing a subset from the larger image directly into the graphics context -- that way at least the transparency is preserved. – Levon Sep 24 '10 at 19:38

2 Answers2

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Sorry I didn't try this code but it should give you the idea:

int[] argbData = new int[ width * height ];
image.getARGB(      argbData,
                    0,
                    width
                    x,
                    y,
                    width,
                    height);

Bitmap result = new Bitmap(width, height);
Graphics g = new Graphics(result);
g.drawARGB(argbData , 0, width, 0, 0, width, height);

return result;
Mahdi Hijazi
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  • Thank you for the code, but the result is absolutely the same -- it does not preserve the transparency and draws white pixels where the transparent area should be. As it stands now, I still haven't found a way to crop an image from a larger image while keeping the transparent parts. – Levon Sep 24 '10 at 18:54
  • Sorry, I can't help but you can check this http://supportforums.blackberry.com/t5/Java-Development/Transparent-background-for-Bitmap/m-p/233113/message-uid/233113 – Mahdi Hijazi Sep 24 '10 at 21:39
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    Instead of creating a Graphics object, could you just do a result.setARGB(...) directly into the new Bitmap? – Marc Novakowski Sep 25 '10 at 04:12
  • Thank you Marc, it worked when I set it directly into the new Bitmap! – Levon Oct 01 '10 at 21:03
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try to use

g.setGlobalAlpha(0);

before 

g.drawBitmap(0, 0, width, height, image, x, y);

or you can use

drawARGB(int[] data, int offset, int scanLength, int x, int y, int width, int height)

which preserve the alpha in the destination image.

Mahdi Hijazi
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  • Thank you, but could you please provide an example of how the int[] data is obtained in the drawARGB(). Thank you! – Levon Sep 24 '10 at 17:11
  • Also, using g.setGlobalAlpha(0) does not work -- it paints the entire area with solid white color. – Levon Sep 24 '10 at 17:41