android - 在 Android 中调整位图大小

Question

我只想调整我从以下名为 Image Loader 的类(使用 Lazy Loadng 方案)获得的位图的大小。我想简单地将我的图像尺寸缩短为 60*60 尺寸。但是当我使用 -

bitmap = Bitmap.createScaledBitmap(bitmap, 20, 25, false);
imageView.setImageBitmap(bitmap);

它和我想要的一样，但是出来的位图非常非常模糊。有没有其他方法可以实现同样的效果。

这是我在 BITMAP dISPLAYER(iNNER cLASS) 中的图像加载器类，我通过上面显示的代码设置图像。

package com.irant.LazyLoading;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Map;
import java.util.Stack;
import java.util.concurrent.ConcurrentHashMap;

import com.irant.a1techno.R;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.graphics.Matrix;
import android.widget.ImageView;



public class ImageLoader {

    MemoryCache memoryCache=new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews = new ConcurrentHashMap<ImageView, String>();

    public ImageLoader(Context context){
        //Make the background thead low priority. This way it will not affect the UI performance
        photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);

        fileCache=new FileCache(context);
    }

    final int stub_id=R.drawable.ic_launcher;
    public void displayImage(String url, Activity activity, ImageView imageView)
    {
        imageViews.put(imageView, url);
        Bitmap bitmap=memoryCache.get(url);
        if(bitmap!=null)
        {
            //bitmap = Bitmap.createScaledBitmap(bitmap, 25, 25, true);
            imageView.setImageBitmap(bitmap);

        }
        else
        {

            queuePhoto(url, activity, imageView);
            imageView.setImageResource(stub_id);
        }    
    }

    private void queuePhoto(String url, Activity activity, ImageView imageView)
    {
        //This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them. 
        photosQueue.Clean(imageView);
        PhotoToLoad p=new PhotoToLoad(url, imageView);
        synchronized(photosQueue.photosToLoad){
            photosQueue.photosToLoad.push(p);
            photosQueue.photosToLoad.notifyAll();
        }

        //start thread if it's not started yet
        if(photoLoaderThread.getState()==Thread.State.NEW)
            photoLoaderThread.start();
    }

    private Bitmap getBitmap(String url) 
    {
        File f=fileCache.getFile(url);
        InputStream is;
        //from SD cache
        Bitmap bitmap=null;
        Bitmap b = decodeFile(f);
        if(b!=null)
            return b;

        //from web
        try {

            System.out.println("---------------------IMAGE URL: "+url);

            URL imageUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
            conn.setConnectTimeout(30000);
            conn.setReadTimeout(30000);
            is=conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = ShrinkBitmap(url, 60, 60);
            bitmap = decodeFile(f);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            bitmap.compress(Bitmap.CompressFormat.JPEG, 40, baos);
            return bitmap;
        } catch (Exception ex){
            System.out.println("---------------------IMAGE URL: "+url);
            ex.printStackTrace();
            //stopThread();
            return null;

        }
        finally{
            bitmap = null;
            is=null;
        }
    }

    Bitmap ShrinkBitmap(String file, int width, int height){

        BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();
        bmpFactoryOptions.inJustDecodeBounds = true;
        Bitmap bitmap = BitmapFactory.decodeFile(file, bmpFactoryOptions);

        int heightRatio = (int)Math.ceil(bmpFactoryOptions.outHeight/(float)height);
        int widthRatio = (int)Math.ceil(bmpFactoryOptions.outWidth/(float)width);

        if (heightRatio > 1 || widthRatio > 1)
        {
            if (heightRatio > widthRatio)
            {
                bmpFactoryOptions.inSampleSize = heightRatio;
            } else {
                bmpFactoryOptions.inSampleSize = widthRatio; 
            }
        }

        bmpFactoryOptions.inJustDecodeBounds = false;
        bitmap = BitmapFactory.decodeFile(file, bmpFactoryOptions);
        return bitmap;
    }

    //decodes image and scales it to reduce memory consumption
    private Bitmap decodeFile(File f){
        try {
            //decode image size
            BitmapFactory.Options o = new BitmapFactory.Options();

            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f),null,o);

            //Find the correct scale value. It should be the power of 2.
            final int REQUIRED_SIZE=70;
            int width_tmp=o.outWidth, height_tmp=o.outHeight;
            int scale=1;
            while(true){
                if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
                    break;
                width_tmp/=2;
                height_tmp/=2;
                scale*=2;
            }

            //decode with inSampleSize
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize=scale;
            return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
        } 
        catch(OutOfMemoryError e)
        {
            e.printStackTrace();
        }catch (FileNotFoundException e) {}
        return null;
    }

    //Task for the queue
    private class PhotoToLoad
    {
        public String url;
        public ImageView imageView;
        public PhotoToLoad(String u, ImageView i){
            url=u; 
            imageView=i;
        }
    }

    PhotosQueue photosQueue=new PhotosQueue();

    public void stopThread()
    {
        photoLoaderThread.interrupt();
    }

    //stores list of photos to download
    class PhotosQueue
    {
        private Stack<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();

        //removes all instances of this ImageView
        public void Clean(ImageView image)
        {
            for(int j=0 ;j<photosToLoad.size();){
                if(photosToLoad.get(j).imageView==image)
                    photosToLoad.remove(j);
                else
                    ++j;
            }
        }
    }

    public class PhotosLoader extends Thread {
        public void run() {
            try {
                while(true)
                {
                    //thread waits until there are any images to load in the queue
                    if(photosQueue.photosToLoad.size()==0)
                        synchronized(photosQueue.photosToLoad){
                            photosQueue.photosToLoad.wait();
                        }
                    if(photosQueue.photosToLoad.size()!=0)
                    {
                        PhotoToLoad photoToLoad;
                        synchronized(photosQueue.photosToLoad){
                            photoToLoad=photosQueue.photosToLoad.pop();
                        }
                        Bitmap bmp=getBitmap(photoToLoad.url);
                        memoryCache.put(photoToLoad.url, bmp);
                        String tag=imageViews.get(photoToLoad.imageView);
                        if(tag!=null && tag.equals(photoToLoad.url)){
                            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
                            Activity a=(Activity)photoToLoad.imageView.getContext();
                            a.runOnUiThread(bd);
                        }
                    }
                    if(Thread.interrupted())
                        break;
                }
            } catch (InterruptedException e) {
                //allow thread to exit
                System.out.println("This is the Exit Point............");
            }
        }
    }

    PhotosLoader photoLoaderThread=new PhotosLoader();

    //Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable
    {
        Bitmap bitmap;
        ImageView imageView;
        public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
        public void run()
        {
            if(bitmap!=null)
            {
                bitmap = Bitmap.createScaledBitmap(bitmap, 20, 25, false);
                imageView.setImageBitmap(bitmap);
            }
            else
                imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }



}

请回复我。 提前致谢

不明白的请不要投反对票。如果有人可以，请帮助我。

谢谢

Answer 1

ImageView 的默认 scaleType 是 FIT_CENTER，这意味着您给 ImageView 的任何图像都会进行缩放，以便其中一个轴(在您的情况下)为 110dp。因此，向它传递一个已缩小到 10*10 的位图将拉伸(stretch)该位图以填充 110*110 空间，而拉伸(stretch)那么大的 10*10 确实会非常模糊。尝试使用其他 scaleType 之一，特别是 CENTER 来查看清晰的正常大小版本的图像:

imageView.setScaleType(ImageView.ScaleType.CENTER);

如果这不是您想要的效果，请知道无论您做什么，缩小图像然后再将其拉伸(stretch)回来总是会使图像质量低于您开始时的质量。 ImageView 类本身已经为您完成了上面代码示例中您似乎试图做的很多事情 - 我鼓励您仔细查看 ScaleTypes 以及它们可以为您做什么