Tess-Two（Android 中的 Tesseract OCR）显示的结果非常不准确

Question

我使用以下函数使用 Tesseract OCR 的 Android 分支 Tess-Two 执行离线 OCR：

private String startOCR(Uri imgUri) {
    try {
        ExifInterface exif = new ExifInterface(imgUri.getPath());
        int exifOrientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
        int rotate = 0;
        switch(exifOrientation) {
            case ExifInterface.ORIENTATION_ROTATE_90:
                rotate = 90;
                break;
            case ExifInterface.ORIENTATION_ROTATE_180:
                rotate = 180;
                break;
            case ExifInterface.ORIENTATION_ROTATE_270:
                rotate = 270;
                break;
        }
        Log.d(TAG, "Rotation: " + rotate);

        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = 4; // 1 - means max size. 4 - means maxsize/4 size. Don't use value <4, because you need more memory in the heap to store your data.
        // set to 300 dpi
        options.inTargetDensity = 300;
        Bitmap bitmap = BitmapFactory.decodeFile(imgUri.getPath(), options);

        // Change Orientation via EXIF
        if (rotate != 0) {

            // Getting width & height of the given image.
            int w = bitmap.getWidth();
            int h = bitmap.getHeight();

            // Setting pre rotate
            Matrix mtx = new Matrix();
            mtx.preRotate(rotate);

            // Rotating Bitmap
            bitmap = Bitmap.createBitmap(bitmap, 0, 0, w, h, mtx, false);

        }

        // To Grayscale
        bitmap = toGrayscale(bitmap);

        final Bitmap b = bitmap;

        final ImageView ivResult = (ImageView)findViewById(R.id.ivResult);
        if(ivResult != null) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    ivResult.setImageBitmap(b);
                }
            });

        }
        return extractText(bitmap);
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
        return "";
    }
}

这里是 extractText() 方法：

private String extractText(Bitmap bitmap) {
    //Log.d(TAG, "extractText");
    try {
        tessBaseApi = new TessBaseAPI();
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
        if (tessBaseApi == null) {
            Log.e(TAG, "TessBaseAPI is null. TessFactory not returning tess object.");
        }
    }

    tessBaseApi.init(DATA_PATH, lang);

    //EXTRA SETTINGS
    tessBaseApi.setVariable(TessBaseAPI.VAR_CHAR_WHITELIST, "abcdefghijklmnopqrstuvwxyz1234567890',.?;/ ");

    Log.d(TAG, "Training file loaded");
    tessBaseApi.setDebug(true);
    tessBaseApi.setPageSegMode(TessBaseAPI.PageSegMode.PSM_AUTO_OSD);
    tessBaseApi.setImage(bitmap);
    String extractedText = "empty result";
    try {
        extractedText = tessBaseApi.getUTF8Text();
    } catch (Exception e) {
        Log.e(TAG, "Error in recognizing text.");
    }
    tessBaseApi.end();
    return extractedText;
}

extractText()返回的值如下图所示：

虽然我在执行 OCR 之前将图像灰度和放大到 300 dpi，但准确度非常低。我怎样才能改善结果？是不是训练出来的数据不够好？

Answer 1

我做了一些测试，但是，我有一些观点和结论可以改善你的结果。

尝试在您的 VAR_WHITE_CHARLIST 变量参数中传递小写和大写字母：

查看此输入的结果：

a) 仅限小写：

参数：

baseApi.setVariable(TessBaseAPI.VAR_CHAR_WHITELIST, "abcdefghijklmnopqrstuvwxyz1234567890',.?;/ ");

结果：

05 atenienses nnito, hdeleto e laicao, os principais acusadores de gocrates, nao defendiam apenas que o filosofo corrompia a juventude; eles lutavam tama bern pelas virtudes da tradigao poetica vinculada a liornero. nristofanes, um dos responsaveis, segundo socrates, dos preconceitos contra o filosofo, era outro grande defensor dessa virtude.

socrates, de certa forma, estava em guerra com a tradieao poetica grega. 0 metodo de socrates era o oposto a narrativa epica de tlornero. sua dialetica nao tinha nada de semideuses corn superpoderes 6

b) 大小写字母：

参数：

baseApi.setVariable(TessBaseAPI.VAR_CHAR_WHITELIST, "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ1234567890',.?;/ ");

结果：

Os atenienses Anito, Meleto e Licao, os principais acusadores de Socrates, nao defendiam apenas que o filosofo corrompia a juventude; eles lutavam tama bern pelas virtudes da tradigao poetica vinculada a Homero. Aristofanes, um dos responsaveis, segundo socrates, dos preconceitos contra o filosofo, era outro grande defensor dessa virtude.

socrates, de certa forma, estava em guerra com a tradieao poetica grega. O metodo de socrates era o Oposto a narrativa epica de Homero. Sua dialetica nao tinha nada de semideuses corn superpoderes 6

PS：我运行这个例子使用的是葡萄牙语，检查一些需要不同字符的词，例如：'é ó ç' 它没有用，因为它不是'作为 char 传递到白名单中。

我也试过运行用你的图片，结果有改善（没那么多）：

Font 20; Which polrlrcran has caplured Ihe curve, summed up a growing mood. In a Ierocrous speech? 'Your iron industry is dead. dead as munon. Your coal yum mono greatly on the iron Vbur Ilk Mary is and. o Your woolen induslry is Why. Your canon Mr Wilding induslry. blmailf

所以我检查了 tesseract 如何将图像二值化：

您的图片有太多噪点，然后 api 尝试对您的图片进行二值化处理，导致图片的很大一部分难以辨认。我建议你再试一次运行，但不要通过灰度，并尝试研究如何减少图像中的噪点。

为了帮助您完成调试任务，您可以保存阈值图像：

WriteFile.writeBitmap(baseApi.getThresholdedImage())

希望对你有用！感谢您分享您的问题！

Abraços!

Answer 2

在这一行 options.inSampleSize = 4; 将数字从 4 更改为 1，然后再次尝试进行 ocr

Tess-Two（Android 中的 Tesseract OCR）显示的结果非常不准确

Tess-Two (Tesseract OCR in Android) shows very inaccurate results

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