Tesseract運行時錯誤：pixReadMemPng中的錯誤：函數不存在

Question

我在Cygwin上構建了Tesseract 3.04.01。它可以識別.bmp文件，但它.png文件失敗：

$ tesseract.exe testing/phototest.png output 
Tesseract Open Source OCR Engine v3.04.01 with Leptonica 
Error in pixReadMemPng: function not present 
Error in pixReadMem: png: no pix returned 
Error during processing.

我認爲leptopnica增加了對PNG支持？

Answer 1

經過一番更深入的研究，結果發現leptonica更像是libpng和libtiff這樣的標準庫的包裝，如果找不到它的lib，會默認禁用支持。

有人給我這個運行./configure時：

checking for png_read_png in -lpng... no

所以我不得不下載和建立的libpng。之後，它仍然沒有工作，因爲libpng安裝在/usr/local/lib，顯然這不是cygwin的默認庫路徑。所以我不得不使用使用LDFLAGS添加：

LDFLAGS=-L/usr/local/lib ./configure 

，它最終與PNG支持建立後，給這個消息：

checking for png_read_png in -lpng... yes 

出於某種原因，在Makefile中混入了鏈接順序 - -lpng -lz，造成連接liblept.la失敗，：

png.c:(.text+0x13ab): undefined reference to `crc32' 

的唯一途徑，我可以解決這個問題是通過運行make V=1（詳細模式）送ee值的實際命令，這是：

make[2]: Entering directory '/home/sasho/leptonica-1.73/src' 
/bin/sh ../libtool --tag=CC --mode=link gcc -g -O2 -no-undefined -version-info 5:0:0 -Wl,--as-needed -L/usr/local/lib -o liblept.la -rpath /usr/local/lib adaptmap.lo affine.lo affinecompose.lo arrayaccess.lo bardecode.lo baseline.lo bbuffer.lo bilateral.lo bilinear.lo binarize.lo binexpand.lo binreduce.lo blend.lo bmf.lo bmpio.lo bmpiostub.lo bootnumgen1.lo bootnumgen2.lo boxbasic.lo boxfunc1.lo boxfunc2.lo boxfunc3.lo boxfunc4.lo bytearray.lo ccbord.lo ccthin.lo classapp.lo colorcontent.lo coloring.lo colormap.lo colormorph.lo colorquant1.lo colorquant2.lo colorseg.lo colorspace.lo compare.lo conncomp.lo convertfiles.lo convolve.lo correlscore.lo dewarp1.lo dewarp2.lo dewarp3.lo dewarp4.lo dnabasic.lo dwacomb.2.lo dwacomblow.2.lo edge.lo encoding.lo enhance.lo fhmtauto.lo fhmtgen.1.lo fhmtgenlow.1.lo finditalic.lo flipdetect.lo fliphmtgen.lo fmorphauto.lo fmorphgen.1.lo fmorphgenlow.1.lo fpix1.lo fpix2.lo gifio.lo gifiostub.lo gplot.lo graphics.lo graymorph.lo grayquant.lo grayquantlow.lo heap.lo jbclass.lo jp2kheader.lo jp2kheaderstub.lo jp2kio.lo jp2kiostub.lo jpegio.lo jpegiostub.lo kernel.lo leptwin.lo libversions.lo list.lo map.lo maze.lo morph.lo morphapp.lo morphdwa.lo morphseq.lo numabasic.lo numafunc1.lo numafunc2.lo pageseg.lo paintcmap.lo parseprotos.lo partition.lo pdfio1.lo pdfio1stub.lo pdfio2.lo pdfio2stub.lo pix1.lo pix2.lo pix3.lo pix4.lo pix5.lo pixabasic.lo pixacc.lo pixafunc1.lo pixafunc2.lo pixalloc.lo pixarith.lo pixcomp.lo pixconv.lo pixlabel.lo pixtiling.lo pngio.lo pngiostub.lo pnmio.lo pnmiostub.lo projective.lo psio1.lo psio1stub.lo psio2.lo psio2stub.lo ptabasic.lo ptafunc1.lo ptra.lo quadtree.lo queue.lo rank.lo rbtree.lo readbarcode.lo readfile.lo recogbasic.lo recogdid.lo recogident.lo recogtrain.lo regutils.lo rop.lo ropiplow.lo roplow.lo rotate.lo rotateam.lo rotateamlow.lo rotateorth.lo rotateshear.lo runlength.lo sarray.lo scale.lo scalelow.lo seedfill.lo seedfilllow.lo sel1.lo sel2.lo selgen.lo shear.lo skew.lo spixio.lo stack.lo stringcode.lo sudoku.lo textops.lo tiffio.lo tiffiostub.lo utils.lo viewfiles.lo warper.lo watershed.lo webpio.lo webpiostub.lo writefile.lo zlibmem.lo zlibmemstub.lo -lz -lpng  

我然後執行相同的命令（從./src作爲當前目錄或它不會工作），但我所附另一個-lz在端部，這導致它成功。之後，我剛剛重新制作，並繼續構建圖書館的其餘部分。

cd src 
/bin/sh ../libtool --tag=CC --mode=link gcc -g -O2 -no-undefined -version-info 5:0:0 -Wl,--as-needed -L/usr/local/lib -o liblept.la -rpath /usr/local/lib adaptmap.lo affine.lo affinecompose.lo arrayaccess.lo bardecode.lo baseline.lo bbuffer.lo bilateral.lo bilinear.lo binarize.lo binexpand.lo binreduce.lo blend.lo bmf.lo bmpio.lo bmpiostub.lo bootnumgen1.lo bootnumgen2.lo boxbasic.lo boxfunc1.lo boxfunc2.lo boxfunc3.lo boxfunc4.lo bytearray.lo ccbord.lo ccthin.lo classapp.lo colorcontent.lo coloring.lo colormap.lo colormorph.lo colorquant1.lo colorquant2.lo colorseg.lo colorspace.lo compare.lo conncomp.lo convertfiles.lo convolve.lo correlscore.lo dewarp1.lo dewarp2.lo dewarp3.lo dewarp4.lo dnabasic.lo dwacomb.2.lo dwacomblow.2.lo edge.lo encoding.lo enhance.lo fhmtauto.lo fhmtgen.1.lo fhmtgenlow.1.lo finditalic.lo flipdetect.lo fliphmtgen.lo fmorphauto.lo fmorphgen.1.lo fmorphgenlow.1.lo fpix1.lo fpix2.lo gifio.lo gifiostub.lo gplot.lo graphics.lo graymorph.lo grayquant.lo grayquantlow.lo heap.lo jbclass.lo jp2kheader.lo jp2kheaderstub.lo jp2kio.lo jp2kiostub.lo jpegio.lo jpegiostub.lo kernel.lo leptwin.lo libversions.lo list.lo map.lo maze.lo morph.lo morphapp.lo morphdwa.lo morphseq.lo numabasic.lo numafunc1.lo numafunc2.lo pageseg.lo paintcmap.lo parseprotos.lo partition.lo pdfio1.lo pdfio1stub.lo pdfio2.lo pdfio2stub.lo pix1.lo pix2.lo pix3.lo pix4.lo pix5.lo pixabasic.lo pixacc.lo pixafunc1.lo pixafunc2.lo pixalloc.lo pixarith.lo pixcomp.lo pixconv.lo pixlabel.lo pixtiling.lo pngio.lo pngiostub.lo pnmio.lo pnmiostub.lo projective.lo psio1.lo psio1stub.lo psio2.lo psio2stub.lo ptabasic.lo ptafunc1.lo ptra.lo quadtree.lo queue.lo rank.lo rbtree.lo readbarcode.lo readfile.lo recogbasic.lo recogdid.lo recogident.lo recogtrain.lo regutils.lo rop.lo ropiplow.lo roplow.lo rotate.lo rotateam.lo rotateamlow.lo rotateorth.lo rotateshear.lo runlength.lo sarray.lo scale.lo scalelow.lo seedfill.lo seedfilllow.lo sel1.lo sel2.lo selgen.lo shear.lo skew.lo spixio.lo stack.lo stringcode.lo sudoku.lo textops.lo tiffio.lo tiffiostub.lo utils.lo viewfiles.lo warper.lo watershed.lo webpio.lo webpiostub.lo writefile.lo zlibmem.lo zlibmemstub.lo -lz -lpng -lz  
cd - 
make