基于MIDP2.0实现图片的缩放功能

 以前在SUN的论坛看到过关于图片缩放的处理，是基于MIDP2.0实现的。今天看到有网友在问这个问题，因此去翻了一下以前的帖子找到了源代码，自己写了一个测试程序验证了一下效果还算可以。希望可以解这位网友的燃眉之急。

    源代码如下：

package com.j2medev.image;

import javax.microedition.lcdui.*;

public class ImageUtil
{

    // fixed point constants
    private static final int FP_SHIFT = 13;

    private static final int FP_ONE = 1 << FP_SHIFT;

    private static final int FP_HALF = 1 << (FP_SHIFT - 1);

    // resampling modes - valid values for the mode parameter of resizeImage()
    // any other value will default to MODE_BOX_FILTER because of the way the
    // conditionals are set in resizeImage()
    public static final int MODE_POINT_SAMPLE = 0;

    public static final int MODE_BOX_FILTER = 1;

    /**
     * getPixels Wrapper for pixel grabbing techniques. I separated this step
     * into it's own function so that other APIs (Nokia, Motorola, Siemens,
     * etc.) can easily substitute the MIDP 2.0 API (Image.getRGB()).
     *
     * @param src
     *            The source image whose pixels we are grabbing.
     * @return An int array containing the pixels in 32 bit ARGB format.
     */
    int[] getPixels(Image src)
    {
        int w = src.getWidth();
        int h = src.getHeight();
        int[] pixels = new int[w * h];
        src.getRGB(pixels, 0, w, 0, 0, w, h);
        return pixels;
    }

    /**
     * drawPixels Wrapper for pixel drawing function. I separated this step into
     * it's own function so that other APIs (Nokia, Motorola, Siemens, etc.) can
     * easily substitute the MIDP 2.0 API (Image.createRGBImage()).
     *
     * @param pixels
     *            int array containing the pixels in 32 bit ARGB format.
     * @param w
     *            The width of the image to be created.
     * @param h
     *            The height of the image to be created. This parameter is
     *            actually superfluous, because it must equal pixels.length / w.
     * @return The image created from the pixel array.
     */
    Image drawPixels(int[] pixels, int w, int h)
    {
        return Image.createRGBImage(pixels, w, h, true);
    }

    /**
     * resizeImage Gets a source image along with new size for it and resizes
     * it.
     *
     * @param src
     *            The source image.
     * @param destW
     *            The new width for the destination image.
     * @param destH
     *            The new heigth for the destination image.
     * @param mode
     *            A flag indicating what type of resizing we want to do. It
     *            currently supports two type: MODE_POINT_SAMPLE - point sampled
     *            resizing, and MODE_BOX_FILTER - box filtered resizing
     *            (default).
     * @return The resized image.
     */
    Image resizeImage(Image src, int destW, int destH, int mode)
    {
        int srcW = src.getWidth();
        int srcH = src.getHeight();

        // create pixel arrays
        int[] destPixels = new int[destW * destH]; // array to hold destination
                                                   // pixels
        int[] srcPixels = getPixels(src); // array with source's pixels

        if (mode == MODE_POINT_SAMPLE)
        {
            // simple point smapled resizing
            // loop through the destination pixels, find the matching pixel on
            // the source and use that
            for (int destY = 0; destY < destH; ++destY)
            {
                for (int destX = 0; destX < destW; ++destX)
                {
                    int srcX = (destX * srcW) / destW;
                    int srcY = (destY * srcH) / destH;
                    destPixels[destX + destY * destW] = srcPixels[srcX + srcY
                            * srcW];
                }
            }
        } else
        {
            // precalculate src/dest ratios
            int ratioW = (srcW << FP_SHIFT) / destW;
            int ratioH = (srcH << FP_SHIFT) / destH;

            int[] tmpPixels = new int[destW * srcH]; // temporary buffer for the
                                                     // horizontal resampling
                                                     // step

            // variables to perform additive blending
            int argb; // color extracted from source
            int a, r, g, b; // separate channels of the color
            int count; // number of pixels sampled for calculating the average

            // the resampling will be separated into 2 steps for simplicity
            // the first step will keep the same height and just stretch the
            // picture horizontally
            // the second step will take the intermediate result and stretch it
            // vertically

            // horizontal resampling
            for (int y = 0; y < srcH; ++y)
            {
                for (int destX = 0; destX < destW; ++destX)
                {
                    count = 0;
                    a = 0;
                    r = 0;
                    b = 0;
                    g = 0; // initialize color blending vars
                    int srcX = (destX * ratioW) >> FP_SHIFT; // calculate
                                                             // beginning of
                                                             // sample
                    int srcX2 = ((destX + 1) * ratioW) >> FP_SHIFT; // calculate
                                                                    // end of
                                                                    // sample

                    // now loop from srcX to srcX2 and add up the values for
                    // each channel
                    do
                    {
                        argb = srcPixels[srcX + y * srcW];
                        a += ((argb & 0xff000000) >> 24); // alpha channel
                        r += ((argb & 0x00ff0000) >> 16); // red channel
                        g += ((argb & 0x0000ff00) >> 8); // green channel
                        b += (argb & 0x000000ff); // blue channel
                        ++count; // count the pixel
                        ++srcX; // move on to the next pixel
                    } while (srcX <= srcX2
                            && srcX + y * srcW < srcPixels.length);

                    // average out the channel values
                    a /= count;
                    r /= count;
                    g /= count;
                    b /= count;

                    // recreate color from the averaged channels and place it
                    // into the temporary buffer
                    tmpPixels[destX + y * destW] = ((a << 24) | (r << 16)
                            | (g << 8) | b);
                }
            }

            // vertical resampling of the temporary buffer (which has been
            // horizontally resampled)
            System.out.println("Vertical resampling...");
            for (int x = 0; x < destW; ++x)
            {
                for (int destY = 0; destY < destH; ++destY)
                {
                    count = 0;
                    a = 0;
                    r = 0;
                    b = 0;
                    g = 0; // initialize color blending vars
                    int srcY = (destY * ratioH) >> FP_SHIFT; // calculate
                                                             // beginning of
                                                             // sample
                    int srcY2 = ((destY + 1) * ratioH) >> FP_SHIFT; // calculate
                                                                    // end of
                                                                    // sample

                    // now loop from srcY to srcY2 and add up the values for
                    // each channel
                    do
                    {
                        argb = tmpPixels[x + srcY * destW];
                        a += ((argb & 0xff000000) >> 24); // alpha channel
                        r += ((argb & 0x00ff0000) >> 16); // red channel
                        g += ((argb & 0x0000ff00) >> 8); // green channel
                        b += (argb & 0x000000ff); // blue channel
                        ++count; // count the pixel
                        ++srcY; // move on to the next pixel
                    } while (srcY <= srcY2
                            && x + srcY * destW < tmpPixels.length);

                    // average out the channel values
                    a /= count;
                    a = (a > 255) ? 255 : a;
                    r /= count;
                    r = (r > 255) ? 255 : r;
                    g /= count;
                    g = (g > 255) ? 255 : g;
                    b /= count;
                    b = (b > 255) ? 255 : b;

                    // recreate color from the averaged channels and place it
                    // into the destination buffer
                    destPixels[x + destY * destW] = ((a << 24) | (r << 16)
                            | (g << 8) | b);
                }
            }
        }

        // return a new image created from the destination pixel buffer
        return drawPixels(destPixels, destW, destH);
    }

}

    有兴趣的网友可以仔细研究一下。我准备了一个图片，然后写了一个测试的MIDlet。下面是效果对比。

 

 

 

 

 

 

 

/*
 * Created on 2004-12-24
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package com.j2medev.image;

import java.io.IOException;

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Image;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

public class TestMIDlet extends MIDlet
{
    private Display display;

    private Form form;

    protected void startApp() throws MIDletStateChangeException
    {
       
        display = Display.getDisplay(this);
        Image srcImage = null;
        try
        {
            srcImage = Image.createImage("/welcome.png");

        } catch (IOException e)
        {
        }
        ImageUtil iu = new ImageUtil();
        form = new Form("Image");
        int width = form.getWidth();
        int height = form.getHeight();
        Image destImage = iu.resizeImage(srcImage, width, height,
                ImageUtil.MODE_POINT_SAMPLE);
        form.append(destImage);
        display.setCurrent(form);

    }

    protected void pauseApp()
    {
      
    }

    protected void destroyApp(boolean arg0) throws MIDletStateChangeException
    {
       

    }

}