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Java Development

Resizing Transparent Bitmaps

by BlackBerry Development Advisor on ‎04-21-2011 07:38 PM (5,467 Views)

Summary

 

This article applies to the following:

 

  • BlackBerry® wireless devices based on Java®

Problem

 

The BlackBerry method Bitmap.scaleInto can create an image with artifacts if the image being scaled contains transprent regions. 

 

This issue has been escalated to our development team for resolution in a future BlackBerry® Device Software Release.

 

Workaround

 

The following class can be used as a workaround. It still uses scaleInto() but in a different manner.  This class is available for download as a .java file.  Use the link at the bottom of the article to access it.

 

package com.patchou.ui;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.Color;
import net.rim.device.api.ui.Graphics;
/**
 *
 * @author    Patchou
 * @version   1.01
 *
 */
public class GPATools
{
    /**
     * Resizes a bitmap with an alpha channel (transparency) without the artifacts introduced
     *   by <code>scaleInto()</code>.
     *
     * @param bmpSrc        Source Bitmap
     * @param nWidth        New Width
     * @param nHeight       New Height
     * @param nFilterType   Filter quality to use. Can be <code>Bitmap.FILTER_LANCZOS</code>,
     *                           <code>Bitmap.FILTER_BILINEAR</code> or
     *                           <code>Bitmap.FILTER_BOX</code>.
     * @param nAspectRatio  Specifies how the picture is resized. Can be
     *                           <code>Bitmap.SCALE_TO_FIT</code>,
     *                           <code>Bitmap.SCALE_TO_FILL</code> or
     *                           <code>Bitmap.SCALE_STRETCH</code>.
     * @return              The resized Bitmap in a new object.
     */
    public static Bitmap ResizeTransparentBitmap(Bitmap bmpSrc, int nWidth, int nHeight, int nFilterType, int nAspectRatio)
    {
        if(bmpsrc== null)
            return null;

        //Get the original dimensions of the bitmap
        int nOriginWidth = bmpSrc.getWidth();
        int nOriginHeight = bmpSrc.getHeight();
if(nWidth == nOriginWidth && nHeight == nOriginHeight)
return bmpSrc;

        //Prepare a drawing bitmap and graphic object
        Bitmap bmpOrigin = new Bitmap(nOriginWidth, nOriginHeight);
        Graphics graph = Graphics.create(bmpOrigin);

        //Create a line of transparent pixels for later use
        int[] aEmptyLine = new int[nWidth];
        for(int x = 0; x < nWidth; x++)
            aEmptyLine[x] = 0x00000000;
        //Create two scaled bitmaps
        Bitmap[] bmpScaled = new Bitmap[2];
        for(int i = 0; i < 2; i++)
        {
            //Draw the bitmap on a white background first, then on a black background
            graph.setColor((i == 0) ? Color.WHITE : Color.BLACK);
            graph.fillRect(0, 0, nOriginWidth, nOriginHeight);
            graph.drawBitmap(0, 0, nOriginWidth, nOriginHeight, bmpSrc, 0, 0);

            //Create a new bitmap with the desired size
            bmpScaled[i] = new Bitmap(nWidth, nHeight);
            if(nAspectRatio == Bitmap.SCALE_TO_FIT)
            {
                //Set the alpha channel of all pixels to 0 to ensure transparency is
                //applied around the picture, if needed by the transformation
                for(int y = 0; y < nHeight; y++)
                    bmpScaled[i].setARGB(aEmptyLine, 0, nWidth, 0, y, nWidth, 1);
            }

            //Scale the bitmap
            bmpOrigin.scaleInto(bmpScaled[i], nFilterType, nAspectRatio);
        }

        //Prepare objects for final iteration
        Bitmap bmpFinal = bmpScaled[0];
        int[][] aPixelLine = new int[2][nWidth];

        //Iterate every line of the two scaled bitmaps
        for(int y = 0; y < nHeight; y++)
        {
            bmpScaled[0].getARGB(aPixelLine[0], 0, nWidth, 0, y, nWidth, 1);
            bmpScaled[1].getARGB(aPixelLine[1], 0, nWidth, 0, y, nWidth, 1);

            //Check every pixel one by one
            for(int x = 0; x < nWidth; x++)
            {
                //If the pixel was untouched (alpha channel still at 0), keep it transparent
                if(((aPixelLine[0][x] >> 24) & 0xff) == 0)
                    aPixelLine[0][x] = 0x00000000;
                else
                {
                    //Compute the alpha value based on the difference of intensity
                    //in the red channel
                    int nAlpha = ((aPixelLine[1][x] >> 16) & 0xff) -
                                    ((aPixelLine[0][x] >> 16) & 0xff) + 255;
                    if(nAlpha == 0)
                        aPixelLine[0][x] = 0x00000000; //Completely transparent
                    else if(nAlpha >= 255)
                        aPixelLine[0][x] |= 0xff000000; //Completely opaque
                    else
                    {
                        //Compute the value of the each channel one by one
                        int nRed = ((aPixelLine[0][x] >> 16 ) & 0xff);
                        int nGreen = ((aPixelLine[0][x] >> 8 ) & 0xff);
                        int nBlue = (aPixelLine[0][x] & 0xff);

                        nRed = (int)(255 + (255.0 * ((double)(nRed-255)/(double)nAlpha)));
                        nGreen = (int)(255 + (255.0 * ((double)(nGreen-255)/(double)nAlpha)));
                        nBlue = (int)(255 + (255.0 * ((double)(nBlue-255)/(double)nAlpha)));

                        if(nRed < 0) nRed = 0;
                        if(nGreen < 0) nGreen = 0;
                        if(nBlue < 0) nBlue = 0;
                        aPixelLine[0][x] = nBlue | (nGreen<<8) | (nRed<<16) | (nAlpha<<24);
                    }
                }
            }

            //Change the pixels of this line to their final value
            bmpFinal.setARGB(aPixelLine[0], 0, nWidth, 0, y, nWidth, 1);
        }
        return bmpFinal;
    }



 

Here's an example of how to call the function:

Bitmap bmp = Bitmap.getBitmapResource("picture.png");
Bitmap bmpResized = GPATools.ResizeTransparentBitmap(bmp, 30, 60,
Bitmap.FILTER_LANCZOS, Bitmap.SCALE_TO_FIT);
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