通过OCR从T恤照片中提取代码

Question

我最近看到有人穿着一件背面印有Perl代码的T恤。我拍了张照片，然后把代码部分裁剪出来了：

接下来，我想通过OCR（光学字符识别）从图片中提取代码，所以我安装了Tesseract OCR和它的Python绑定库pytesser。

Pytesser只支持TIFF格式的图片，所以我在Gimp里把图片转换成了TIFF格式，然后输入了以下代码（Ubuntu 9.10）：

>>> from pytesser import *
>>> image = Image.open('code.tif')
>>> print image_to_string(image)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pytesser.py", line 30, in image_to_string
    util.image_to_scratch(im, scratch_image_name)
  File "util.py", line 7, in image_to_scratch
    im.save(scratch_image_name, dpi=(200,200))
  File "/usr/lib/python2.6/dist-packages/PIL/Image.py", line 1406, in save
    save_handler(self, fp, filename)
  File "/usr/lib/python2.6/dist-packages/PIL/BmpImagePlugin.py", line 197, in _save
    raise IOError("cannot write mode %s as BMP" % im.mode)
IOError: cannot write mode RGBA as BMP
>>> r,g,b,a = image.split()
>>> img = Image.merge("RGB", (r,g,b))
>>> print image_to_string(img)
Tesseract Open Source OCR Engine

     éi     _   l_` _ t  
  ’   ‘" fY`  
  {  W       IKQW
  ·  __·_  ‘ ·-»·      
       :W   Z  
  ··  I  A n   1   
           ;f        
     `    `      
`T     .' V   _ ‘  
I  {Z.; » ;,. , ;  y i-   4 : %:,,    
      `· »    V; ` ?    
‘,—·.    
H***li¥v·•·}I§¢   ` _  »¢is5#__·¤G$++}§;“»‘7·
  71   ’    Q  {  NH IQ
  ytéggygi {     ;g¤qg;gm·;,g(g,,3) {3;;+-
   § {Jf**$d$ }‘$p•¢L#d¤ Sc}
  »   i `  i A1:

但是，OCR引擎输出的结果明显是一堆乱码。那么，我的问题是：

• 我该怎么做才能从Tesseract获得更好的OCR结果？
• 或者，有没有其他人用其他方法从上面的图片中提取代码更顺利？

Answer 1

RedDwight 代码里有几个小错误。

#!/usr/bin/perl
(my $d=q[AA                GTCAGTTCCT
  CGCTATGTA                 ACACACACCA
    TTTGTGAGT                ATGTAACATA
      CTCGCTGGC              TATGTCAGAC
        AGATTGATC          GATCGATAGA
          ATGATAGATC     GAACGAGTGA
            TAGATAGAGT GATAGATAGA
              GAGAGA GATAGAACGA
                TC GATAGAGAGA
                 TAGATAGACA G
               ATCGAGAGAC AGATA
             GAACGACAGA TAGATAGAT
           TGAGTGATAG    ACTGAGAGAT
         AGATAGATTG        ATAGATAGAT
       AGATAGATAG           ACTGATAGAT
     AGAGTGATAG             ATAGAATGAG
   AGATAGACAG               ACAGACAGAT
  AGATAGACAG               AGAGACAGAT
  TGATAGATAG             ATAGATAGAT
  TGATAGATAG           AATGATAGAT
   AGATTGAGTG        ACAGATCGAT
     AGAACCTTTCT   CAGTAACAGT
       CTTTCTCGC TGGCTTGCTT
         TCTAA CAACCTTACT
           G ACTGCCTTTC
           TGAGATAGAT CGA
         TAGATAGATA GACAGAC
       AGATAGATAG  ATAGAATGAC
     AGACAGAGAG      ACAGAATGAT
   CGAGAGACAG          ATAGATAGAT
  AGAATGATAG             ACAGATAGAC
  AGATAGATAG               ACAGACAGAT
  AGACAGACTG                 ATAGATAGAT
   AGATAGATAG                 AATGACAGAT
     CGATTGAATG               ACAGATAGAT
       CGACAGATAG             ATAGACAGAT
         AGAGTGATAG          ATTGATCGAC
           TGATTGATAG      ACTGATTGAT
             AGACAGATAG  AGTGACAGAT
               CGACAGA TAGATAGATA
                 GATA GATAGATAG
                    ATAGACAGA G
                  AGATAGATAG ACA
                GTCGCAAGTTC GCTCACA
])=~s/\s+//g;%a=map{chr $_=>$i++}65,84,67,
71;$p=join$;,keys%a;while($d=~/([$p]{4})/g
){next if$j++%96>=16;$c=0;for$d(0..3){$c+=
$a{substr($1,$d,1)}*(4**$d)}$perl.=chr $c}
             eval $perl;

运行后会产生：

Just another genome hacker.

Answer 2

预处理肯定会让图像变得更好用。

比如说，这里是用Gimp软件的“色阶”、“高斯差分”和“色阶”滤镜处理后的图像效果。

Answer 3

你可能打字的速度比整理图片和安装OCR引擎的速度还要快：

#!/usr/bin/perl
(my$d=q[AA                GTCAGTTCCT
  CGCTATGTA                 ACACACACCA
    TTTGTGAGT                ATGTAACATA
      CTCGCTGGC              TATGTCAGAC
        AGATTGATC          GATCGATAGA
          ATGATAGATC     GAACGAGTGA
            TAGATAGAGT GATAGATAGA
              GAGAGA GATAGAACGA
                TC GATAGAGAGA
                 TAGATAGACA G
               ATCGAGAGAC AGATA
             GAACGACAGA TAGATAGAT
           TGAGTGATAG    ACTGAGAGAT
         AGATAGATTG        ATAGATAGAT
       AGATAGATAG           ACTGATAGAT
     AGAGTGATAG             ATAGAATGAG
   AGATAGACAG               ACAGACAGAT
  AGATAGACAG               AGAGACAGAT
  TGATAGATAG             ATAGATAGAT
  TGATAGATAG           AATGATAGAT
   AGATTGAGTG        ACAGATCGAT
     AGAACCTTTCT   CAGTAACAGT
       CTTTCTCGC TGGCTTGCTT
         TCTAA CAACCTTACT
           G ACTGCCTTTC
           TGAGATAGAT CGA
         TAGATAGATA GACAGAC
       AGATAGATAG  ATAGAATGAC
     AGACAGAGAG      ACAGAATGAT
   CGAGAGACAG          ATAGATAGAT
  AGAATGATAG             ACAGATAGAC
  AGATAGATAG               ACAGACAGAT
  AGACAGACTG                 ATAGATAGAT
   AGATAGATAG                 AATGACAGAT
     CGATTGAATG               ACAGATAGAT
       CGACAGATAG             ATAGACAGAT
         AGAGTGATAG          ATTGATCGAC
           TGATTGATAG      ACTGATTGAT
             AGACAGATAG  AGTGACAGAT
               CGACAGA TAGATAGATA
                 GATA GATAGATAG
                    ATAGACAGA G
                  AGATAGATAG ACA
                GTCGCAAGTTC GCTCACA
])=~s/\s+//g;%a=map{chr $_=>$i++}65,84,67,
71;$p=join$;,keys%a;while($d=~/([$p]{4})/g
){next if$j++%96>=16;$c=0;for$d(0..3){$c+=
$a{substr($1,$d,1)}*(4**$d)}$perl.=chr $c}
             eval $perl;

补充：有个错别字。