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基于MIDP2.0实现图片的缩放功能

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

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

{

}

}

(出处:http://www.knowsky.com)

 
 
 
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