Android中的二值化图像

Question

我正在开发使用tesseract OCR从图像扫描文本的android应用程序,
我听说在对它执行OCR之前对图像进行二值化会得到更好的结果,
所以我开始寻找执行操作的代码,

我发现很少,但它实际上在java中,需要awt库...所以他们不能在android上工作.
你能帮我找一个吗？
谢谢

Answer 1

作为一个项目的一部分,我必须做一个类似的任务.我在我的工作区找到了这段代码,我想这就是你需要的:

Bitmap img = BitmapFactory.decodeResource(this.getResources(), drawable.testimage);
Paint paint = new Paint();

ColorMatrix cm = new ColorMatrix();
float a = 77f;
float b = 151f;
float c = 28f;
float t = 120 * -256f;
cm.set(new float[] { a, b, c, 0, t, a, b, c, 0, t, a, b, c, 0, t, 0, 0, 0, 1, 0 });
paint.setColorFilter(new ColorMatrixColorFilter(cm));
canvas.drawBitmap(img, 0, 0, paint);

在这里,我使用ColorMatrix从彩色图像生成黑白图像.我还发现这段代码用于将彩色图像转换为灰度图像:

Bitmap result = Bitmap.createBitmap(destWidth, destHeight,Bitmap.Config.RGB_565);
RectF destRect = new RectF(0, 0, destWidth, destHeight);
Canvas canvas = new Canvas(result);
Paint paint = new Paint();
ColorMatrix colorMatrix = new ColorMatrix();
colorMatrix.setSaturation(0);
ColorFilter filter = new ColorMatrixColorFilter(colorMatrix);
paint.setColorFilter(filter);
canvas.drawBitmap(bitmap, sourceRect, destRect, paint); 

希望这对你有所帮助.

Answer 2

一个简单的解决方案

下面，我简单地根据正常的 3 维空间距离公式更改图像中的每个像素。我根据像素与每种颜色的距离来决定该像素应该是黑色还是白色。例如，(1,2,3) 比 (255,255,255) 更接近 (0,0,0)，因此被判定为黑色。我确信还有更聪明的算法。这只是一个简单的

MainActivity.java

package com.example.binarizeimage;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Environment;
import android.widget.ImageView;

import com.example.binarizeimage.R.drawable;

/**
 * @author Sherif elKhatib - shush
 *
 */
public class MainActivity extends Activity {
    /**
     * Boolean that tells me how to treat a transparent pixel (Should it be black?)
     */
    private static final boolean TRASNPARENT_IS_BLACK = false;
    /**
     * This is a point that will break the space into Black or white
     * In real words, if the distance between WHITE and BLACK is D;
     * then we should be this percent far from WHITE to be in the black region.
     * Example: If this value is 0.5, the space is equally split.  
     */
    private static final double SPACE_BREAKING_POINT = 13.0/30.0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //this is the original image
        Bitmap theOriginalImage = BitmapFactory.decodeResource(this.getResources(), drawable.ic_launcher);
        //this is the image that is binarized
        Bitmap binarizedImage = convertToMutable(theOriginalImage);
        // I will look at each pixel and use the function shouldBeBlack to decide 
        // whether to make it black or otherwise white
        for(int i=0;i<binarizedImage.getWidth();i++) {
            for(int c=0;c<binarizedImage.getHeight();c++) {
                int pixel = binarizedImage.getPixel(i, c);
                if(shouldBeBlack(pixel))
                    binarizedImage.setPixel(i, c, Color.BLACK);
                else
                    binarizedImage.setPixel(i, c, Color.WHITE);
            }
        }


        ImageView iv = (ImageView) findViewById(R.id.imageView1);
        ImageView ivb = (ImageView) findViewById(R.id.ImageView01);
        //show the original image
        iv.setImageBitmap(BitmapFactory.decodeResource(this.getResources(), drawable.ic_launcher));
        //show the binarized image
        ivb.setImageBitmap(binarizedImage);
    }
    /**
     * @param pixel the pixel that we need to decide on
     * @return boolean indicating whether this pixel should be black
     */
    private static boolean shouldBeBlack(int pixel) {
        int alpha = Color.alpha(pixel);
        int redValue = Color.red(pixel);
        int blueValue = Color.blue(pixel);
        int greenValue = Color.green(pixel);
        if(alpha == 0x00) //if this pixel is transparent let me use TRASNPARENT_IS_BLACK
            return TRASNPARENT_IS_BLACK;
        // distance from the white extreme
        double distanceFromWhite = Math.sqrt(Math.pow(0xff - redValue, 2) + Math.pow(0xff - blueValue, 2) + Math.pow(0xff - greenValue, 2));
        // distance from the black extreme //this should not be computed and might be as well a function of distanceFromWhite and the whole distance
        double distanceFromBlack = Math.sqrt(Math.pow(0x00 - redValue, 2) + Math.pow(0x00 - blueValue, 2) + Math.pow(0x00 - greenValue, 2));
        // distance between the extremes //this is a constant that should not be computed :p
        double distance = distanceFromBlack + distanceFromWhite;
        // distance between the extremes
        return ((distanceFromWhite/distance)>SPACE_BREAKING_POINT);
    }
    /**
     * @author Derzu
     * 
     * @see http://stackoverflow.com/a/9194259/833622
     * 
     * Converts a immutable bitmap to a mutable bitmap. This operation doesn't allocates
     * more memory that there is already allocated.
     * 
     * @param imgIn - Source image. It will be released, and should not be used more
     * @return a copy of imgIn, but muttable.
     */
    public static Bitmap convertToMutable(Bitmap imgIn) {
        try {
            //this is the file going to use temporally to save the bytes. 
            // This file will not be a image, it will store the raw image data.
            File file = new File(Environment.getExternalStorageDirectory() + File.separator + "temp.tmp");

            //Open an RandomAccessFile
            //Make sure you have added uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
            //into AndroidManifest.xml file
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");

            // get the width and height of the source bitmap.
            int width = imgIn.getWidth();
            int height = imgIn.getHeight();
            Config type = imgIn.getConfig();

            //Copy the byte to the file
            //Assume source bitmap loaded using options.inPreferredConfig = Config.ARGB_8888;
            FileChannel channel = randomAccessFile.getChannel();
            MappedByteBuffer map = channel.map(MapMode.READ_WRITE, 0, imgIn.getRowBytes()*height);
            imgIn.copyPixelsToBuffer(map);
            //recycle the source bitmap, this will be no longer used.
            imgIn.recycle();
            System.gc();// try to force the bytes from the imgIn to be released

            //Create a new bitmap to load the bitmap again. Probably the memory will be available. 
            imgIn = Bitmap.createBitmap(width, height, type);
            map.position(0);
            //load it back from temporary 
            imgIn.copyPixelsFromBuffer(map);
            //close the temporary file and channel , then delete that also
            channel.close();
            randomAccessFile.close();

            // delete the temp file
            file.delete();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 

        return imgIn;
    }
}

*活动_main.xml*

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView2"
        android:layout_centerHorizontal="true"
        android:text="Original Image" />

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_centerHorizontal="true"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/TextView02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView1"
        android:layout_below="@+id/imageView1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="28dp"
        android:text="YES/NO Image" />

    <ImageView
        android:id="@+id/ImageView01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/TextView02"
        android:layout_centerHorizontal="true"
        android:src="@drawable/ic_launcher" />

</RelativeLayout>